ALBERT

Notes: Abstract In the framework of the neural network theory effects similar to hypnotic displays are constructed. They are based on the associative paradigm involving non-linear interaction of excitatory and inhibitory channels with synaptic memory. The non-linearity of long-term memorizing processes may cause effects exhibited by blind spots, which are interpreted as the first stage of hypnosis. More complicated phenomena are discussed in terms of a two-layer network.

Notes: Abstract Mutation is introduced into autocatalytic reaction networks. The differential equations obtained are neither of repliator-type nor can they be transformed straightway into a linear equation. Examples of low dimensional dynamical systems —n=2, 3 and 4 — are discussed and complete qualitative analysis is presented. Error thresholds known from simple replication-mutation kinetics with frequency independent replication rates occur here as well. Instead of cooperative transitions or higher order phase transitions the thresholds appear here as supercritical or subcritical bifurcations being analogous to first-order phase transitions.

Notes: Abstract The non-linear behavior of a differential equations-based predator-prey model, incorporating a spatial refuge protecting a consant proportion of prey and with temperature-dependent parameters chosen appropriately for a mite interaction on fruit trees, is examined using the numerical bifurcation code AUTO 86. The most significant result of this analysis is the existence of a temperature interval in which increasing the amount of refuge dynamically destabilizes the system; and on part of this interval the interaction is less likely to persist in that predator and prey minimum population densities are lower than when no refuge is available. It is also shown that increasing the amount of refuge can lead to population outbreaks due to the presence of multiple stable states. The ecological implications of a refuge are discussed with respect to the biological control of mite pests.

Notes: Abstract In many applications of control theory on plant growth models biomass maximization is postulated to avoid analytically unsolvable problems while fruit maximization is commonly considered to be a more realistic criterion. In a special case, we are able to compare these criteria. Iwasa and Roughgarden (1984,Theor. Pop. Biol. 25, 78–105) have investigated a certain class of plant growth models using a fruit maximization criterion. They proved that, in the vegetative growth period, the organs follow a certain path of balanced growth. We show that this path remains optimal when biomass maximization is postulated. This underlines the importance of the balanced growth path found by Iwasa and Roughgarden. Furthermore, our result suggests that in the vegetative growth period the biomass maximization criterion is a good approximation of fruit maximization. In another theoretical control investigation, Schultzeet al. (1983,Oecologia 58, 169–177) derived a different type of balanced growth path. We apply the theory of Iwasa and Roughgarden to an improved version of the model of Schulzeet al. This leads to a new description of balanced growth between root and shoot that reflects non-linearities in the water uptake process and constitutes an interesting hypothesis for further experimental testing.

Notes: Abstract In this paper the effects of changing the ion concentration in and around a sample of soft tissue are investigated. The triphasic theory developed by Laiet al. (1990,Biomechanics of Diarthrodial Joints, Vol. 1, Berlin, Springer-Verlag) is reduced to two coupled partial differential equations involving fluid ion concentration and tissue solid deformation. These equations are given in general form for Cartesian, cylindrical and spherical geometries. After solving the two equations quantities such as fluid velocity, fluid pressure, chemical potentials and chemical expansion stress may be easily calculated. In the Cartesian geometry comparison is made with the experimental and theoretical work of Myerset al. (1984,ASME J. biomech. Engng,106, 151–158). This dealt with changing the ion concentration of a salt shower on a strip of bovine articular cartilage. Results were obtained in both free swelling and isometric tension states, using an empirical formula to acount for ion induced deformation. The present theory predicts lower ion concentrations inside the tissue than this earlier work. A spherical sample of tissue subjected to a change in salt bath ion concentration is also considered. Numerical results are obtained for both hypertonic and hypotonic bathing solutions. Of particular interest is the finding that tissue may contract internally before reaching a final swollen equilibrium state or swell internally before finally contracting. By considering the relative magnitude, and also variation throughout the time course of terms in the governing equations, an even simpler system is deduced. As well as being linear the concentration equation in the new system is uncoupled. Results obtained from the linear system compare well with those from the spherical section. Thus, biological swelling situations may be modelled by a simple system of equations with the possibility, of approximate analytic solutions in certain cases.

Notes: Abstract Many models of immune networks have been proposed since the original work of Jerne [1974,Ann. Immun. (Inst. Pasteur) 125C, 373–389]. Recently, a limited class of models (Weisbuchet al., 1990,J. theor. Biol. 146, 483–499) have been shown to maintain immunological memory by idiotypic network interactions. We examine generalizations of these models when the networks are both large and highly connected to study their memory capacity, i.e. their ability to account for immunization to a large number of random antigens. Our calculations show that in these minimal models, random connectivities with continuously distributed affinities reduce the memory capacity to essentially nil.

Notes: Abstract A kinetic model is proposed to delineate the factors that determine the coronary reactive hyperemic response (RHR) to transient ischemia. The model comprises of myocardial-interstitial (M) and vascular (V) compartments. Vasodilator metabolites (VM) are produced in the M compartment during the interval of coronary occlusion. The rate of VM production is dependent on the flow rate during the ischemic period, the ratio of excess flow above the control level (R) to the loss of flow during occlusion period (D), the amount of oxygen stored and the degree of vasodilation in the V compartment prior to occlusion. Following a complete release of occlusion, VM are transported from the M to V compartment and are washed out or degraded with time. The time course of RHR is determined by the coronary patency which is proportional to VM concentration in the V compartment. Based on a set of numerical constants, the model is tested by simulating RHR to the various occlusion manoeuvres: a pair of 10 sec occlusions separated by brief release, a 15 sec release followed by a second brief occlusion, a brief release of an occlusion followed by restriced inflow and a period of restricted inflow after occlusion. The simulated results fit the experimental R/D and RH durations data of canine hearts. Factors that determine the impairment of RH capacity in coronary stenosis are suggested in terms of the model scheme.

Notes: Abstract In the present paper a kinetic study is made of the behaviour of a Michaelis-Menten enzyme-catalysed reaction in the presence of irreversible inhibitors rendered unstable in the medium by their reaction with the product of enzymatic catalysis. A general mechanism involving competitive, non-competitive, uncompetitive and mixed irreversible inhibition with one or two steps has been analysed. The differential equation that describes the kinetics of the reaction is non-linear and computer simulations of its dynamic behaviour are presented. The results obtained show that the systems studied here present kinetic co-operativity for a target enzyme that follows the simple Michaelis-Menten mechanism in its action on the substrate, except in the case of an uncompetitive-type inhibitor.

Notes: Abstract The relative contributions of mitochondrial β-oxidation and peroxisomal β-oxidation and peroxisomal ω-oxidation to the oxidation of a given fatty acidin vivo can be quantitated by an isotopic method. The approach requires infusion of a fatty acid labelled on two specific carbon atoms (e.g. [1-14C] and [11-14C] palmitate) to an isotopic steady state, with subsequent isolation and degradation of an acetylated conjugate as a product of the liver cytosolic acetyl CoA pool and of ketone bodies as a product of the liver mitochondrial acetyl CoA pool.

Notes: Abstract Pancreatic β-cells in intact islets of Langerhans perfused with various glucose concentrations exhibit periodic bursting electrical activity (BEA) consisting of active and silent phases. The fraction of the time spent in the active phase is called the plateau fraction and appears to be strongly correlated with the rate of release of insulin from islets as glucose concentration is varied. Here this correlation is quantified and a theoretical development is presented in detail. Experimental rates of insulin release are correlated with “effective” plateau fractions over a range of glucose concentrations. There are a number of different models for BEA in pancreatic β-cells and a method is developed here to quantify the dependence of a glucose dependent parameter on glucose concentration. As an example, the plateau fractions computed from the Sherman-Rinzel-Keizer model are matched with experimental plateau fractions to obtain a relationship between the model's glucose-dependent parameter, β, and glucose concentration. Knowledge of the relationships between β and glucose concentration and between experimental measurements of rates of insulin release and plateau fractions permits the determination of theoretical rates of insulin release from the model.

Notes: Abstract When a suspension of bacterial cells of the speciesBacillus subtilis is placed in a chamber with its upper surface open to the atmosphere complex bioconvection patterns are observed. These arise because the cells: (1) are denser than water; and (2) usually swim upwards, so that the density of an initially uniform suspension becomes greater at the top than the bottom. When the vertical density gradient becomes large enough, an overturning instability occurs which ultimately evolves into the observed patterns. The reason that the cells swim upwards is that they are aerotactic, i.e. they swim up gradients of oxygen, and they consume oxygen. These properties are incorporated in conservation equations for the cell (N) and oxygen (C) concentrations, and these are solved in the pre-instability phase of development whenN andC depend only on the vertical coordinate and time. Numerical results are obtained for both shallow- and deep-layer chambers, which are intrinsically different and require different mathematical and numerical treatments. It is found that, for both shallow and deep chambers, a thin boundary layer, densely packed with cells, forms near the surface. Beneath this layer the suspension becomes severely depleted of cells. Furthermore, in the deep chamber cases, a discontinuity in the cell concentration arises between this cell-depleted region and a cell-rich region further below, where no significant oxygen concentration gradients develop before the oxygen is fully consumed. The results obtained from the model are in good qualitative agreement with the experimental observations.

Notes: Abstract We describe a classification scheme for bursting oscillations which encompasses many of those found in the literature on bursting in excitable media. This is an extension of the scheme of Rinzel (inMathematical Topics in Population Biology, Springer, Berlin, 1987), put in the context of a sequence of horizontal cuts through a two-parameter bifurcation diagram. We use this to describe the phenomenological character of different types of bursting, addressing the issue of how well the bursting can be characterized given the limited amount of information often available in experimental settings.

Notes: Abstract To ensure its sustained growth, a tumour may secrete chemical compounds which cause neighbouring capillaries to form sprouts which then migrate towards it, furnishing the tumour with an increased supply of nutrients. In this paper a mathematical model is presented which describes the migration of capillary sprouts in response to a chemoattractant field set up by a tumour-released angiogenic factor, sometimes termed a tumour angiogenesis factor (TAF). The resulting model admits travelling wave solutions which correspond either to successful neovascularization of the tumour or failure of the tumour to secure a vascular network, and which exhibit many of the characteristic features of angiogenesis. For example, the increasing speed of the vascular front, and the evolution of an increasingly developed vascular network behind the leading capillary tip front (the brush-border effect) are both discernible from the numerical simulations. Through the development and analysis of a simplified caricature model, valuable insight is gained into how the balance between chemotaxis, tip proliferation and tip death affects the tumour's ability to induce a vascular response from neighbouring blood vessels. In particular, it is possible to define the success of angiogenesis in terms of known parameters, thereby providing a potential framework for assessing the viability of tumour neovascularization in terms of measurable quantities.

Notes: Abstract The formation of neuronal networks requires axonal growth towards target neutons. A simple set of grammar rules is introduced to describe axonal growth towards target cells situated both at short and long distances from the growing neuron. Growth for short distances is descrbed by growth following the highest gradient of a chemical compound (which is spread by diffusion from the targets). This approach fails to describe long-distance growth, which is addressed by adopting a graph grammar theory for growing trees. With these rules a flexible tool to draw network of neurons by computer can be developed.

Notes: Abstract A pair of growth control triads are used to describe coincident tumor growth and liver regeneration after partial hepatectomy. The models are extensions of previous growth control models which describe tumor growth in an unperturbed host (Michelson and Leith, 1991,Bull. math. Biol. 53, 639–656; idem, 1992, Proceedings of the Third International Conference on Communications and Control, Vol. 2, pp. 481–490; idem, 1992,Bull. math. Biol. 55, 993–1011; idem,J. theor. Biol. 169, 327–338). The linkage between the two triads depends upon systemic signals carried by soluble factors, and mathematical descriptors based upon biological first principals are proposed. The sources of the growth factors, their targets and the processing of their signals are investigated. Analyses of equilibrium in the constant coefficients case and simulated growth curves for the dynamic system are presented, and the effects of growth factor-induced mitogenesis and angiogenesis are discussed in particular. A case is made for early and late responses in the coupled control system. The biology of the signal processing paradigm is placed within a new theoretical context and discussed with regard to tumor adaptation, liver differentiation and the development of a tumor hypoxic fraction.

Notes: Abstract We consider the problem of optimal stabilization and control of populations which follow the Leslie model dynamics, within state space and control systems theory and methodology. Various types of culling strategies are formulated and introduced into the Leslie model as control inputs, and their effect on global asymptotic stability is investigated. Our new approach provides answers to several unexplored problems. We show that in general it is possible to achieve a desired stable equilibrium population level, through the design of a class ofshifted-proportional stabilizing culling policies. Further, we formulate general non-linear constrained opitmization problems, for obtaining the cost-optimal policy among this generally infinite class of such stabilizing policies. The theoretical findings are illustrated through the solution of the problem over an infinite planning horizon for a numerical example. A comparative study of the costs and dynamic effects of various culling strategies also supports the mathematical results.

Notes: Abstract A new approach for data assimilation, which is based on the adjoint method, but allows the computer code for the adjoint to be constructed directly from the model computer code, is described. This technique is straightforward and reduces the chance of introducing errors in the construction of the adjoint code. Implementation of the technique is illustrated by applying it to a simple predator-prey model in a model fitting mode. A series of identical twin numerical experiments are used to show that this data assimilation approach can successfully recover model parameters as well as initial conditions. However, the ease with which these values are recovered is dependent on the form of the model equations as well as on the type and amount of data that are available. Additional numerical experiments show that sufficient coefficient and parameter recoveries are possible even when the assimilated data contain significant random noise. Thus, for biological systems that can be described by ecosystem models, the adjoint method represents a powerful approach for estimating values for little-known biological parameters, such as initial conditions, growth rates, and mortality rates.

Notes: Abstract The effect of group size on behavioral parameters of the Oriental hornet,Vespa orientalis, was assessed experimentally under laboratory conditions. Hornet groups of various sizes (ranging from 1 to 100 individuals per group) comprised of young individuals (0–24 hr of age) devoid of a queen were placed in artificial breeding boxes (ABBs). The following three quantitative parameters were evaluated: the amount and rate of building as a function of the number of hornets in the group, the rate of oviposition as, related to group size and the longevity of hornets as a function of their group size. The probability for the occurrence of these events was similarly considered and additional behavioral parameters were only assessed qualitatively. Results of this investigation revealed a relation between the three mentioned quantitative behavioral parameters and the number of hornets per group. The number of hornets per group was positively related to the extent of building, the number of cells built by a group is $$2\pi \sqrt {group size} $$ , but negatively related to the rate of building. As for the delay of building, a non-monotone relation was found. The relation between number of hornets per group and the oviposition delay was found to be non-monotone; the number of hornets per group and their longevity were found to be inversely related. Discrepanices were recorded on the very small (1–2 individuals) or very large (100 individuals) hornet groups.

Notes: Abstract A new method for reconstructing evolutionary relationship among bacteria by use of rRNA sequence data is proposed. The method is based on the concept of fuzzy classification of probabilitiesp(i), p(i/j) andp(i/j*) (i=A,G,C,U) of each sequence. The resulting partition tree shares common features of previous works but has some new peculiarities.

Notes: Abstract We describe the behaviour of motile microorganisms (e.g. flagellates) attracted by “gyrotaxis” to a sinking, non-motile particle (e.g. an algal cell). The model is based on the application of Stokes' solution for the flow field around the settling cell. The volume within which the flagellate is attracted to the sinking particle is determined from the trajectories of the flagellate. The model of gyrotaxis has several applications; these include the colonization of sinking marine snow particles with motile microoganisms and suspension feeding by protozoa.

Notes: Abstract The effect of varying habitat dimensionality on the dynamics of a model predator-prey system is examined using an individual-based simulation. The general results are that in one dimension fluctuations in abundance of prey and predators occur over a large range of spatial scales (extinctions occur over many spatial scales). In two dimensions (and low mobilities of prey and predators) the dynamics become more predictably periodic at local scales and constant at larger scales due to statistical stabilization. In three dimensions, the model can become “phase-locked” with prey and predators displaying oscillations in abundance over large spatial scales.

Notes: Abstract A rather complete model of the gluconeogenic pathway was used, with the known separate pools of mitochondrial and cytosolic oxalacetate, malate and aspartate. The fumarase, malate dehydrogenase and glutamate oxalacetate transaminase reactions were assumed to be isotopically actively reversible, but none at isotopic equilibrium. Malate was assumed to exchange actively between the mitochondrial and cytosol, while aspartate exchange was more limited, in agreement with the known electrogenic nature of aspartate export from the mitochondria. This model was fit to14C data obtained in hepatocyte studies, and to the whole rat14C data obtained by Heath and Rose (Biochem J. 227, 851–876, 1985). The latter data were easily fit to our model, when a single mitochondrial oxalacetate pool was assumed. However, invoking two mitochondrial oxalacetate pools, as proposed by Heath and Rose, with the oxalacetate formed via pyruvate carboxylase preferentially channelled to gluconeogenesis, could not be fit with the known differences in scrambling in glucose and glutamate produced from L[3-14C]lactate.

Notes: Abstract Oscillatory secretion of insulin has been observed in many different experimental preparations ranging from pancreatic islets to the whole pancreas. Here we examine the mathematical features underlying a possible model for oscillatory secretion from the perifused, insulin-secreting cell line, HIT-15. The model includes the kinetics of uptake of glucose by GLUT transporters, the rate of glucose metabolism within the cell, and the effect of glucose on the rate of insulin secretion. Putative feedback by insulin on the rate of glucose transport into the cells is treated phenomenologically and leads to insulin oscillations similar to those observed experimentally in HIT cells. The resulting set of ordinary differential equations is simplified by time-scale analysis to a two-variable set of ordinary differential equations. Because of this simplification we can explore, in great detail, the characteristics of the oscillations and their sensitivity to parameter variation using phase plane analysis.

Notes: Abstract The fluid dynamics of sperm motility near both rigid and elastic walls is studied using the immersed boundary method. Simulations of both single and interacting organisms are presented. In particular, we find that nearby organisms originally undulating with a 90° phase shift may adjust their relative swimming velocities and phase-lock. Comparisons with previous analytical results are also discussed. The tendency of a near-wall to attract organisms is demonstrated.

Notes: Abstract The secondary immune response is one of the most important features of immune systems. During the secondary immune response, the immune system can eliminate the antigen, which has been encountered by the individual during the primary invasion, more rapidly and efficiently. Both T and B memory cells contribute to the secondary response. In this paper, we only concentrate on the functions of memory B cells. We explore a model describing the memory contributed by the specific long-lived clone which is maintained by continued stimulation with a small amount of antigens sequestered on the surfaces of the follicular dendritic cells (FDC). The behavior of the secondary response provided by the model can be compared with experimental observations. The model shows that memory B cells indeed play an important role in the secondary response. It is found that a single memory cell in a long-lived clone may not be long-lived. In the present note, the influences of relevant parameters on the secondary response are also explored.

Notes: Abstract A biological system consisting of a population of cells suspended in a liquid substrate is considered. The general problem addressed in the paper is the derivation of the kinetic pattern of population growth as a statistical effect of a very large number of elementary interactions between a single cell and the molecules of nutrient in substrate. Solution of the problem is obtained in the form of equation expressing the population growth ratec as a function of substrate concentration,C s. The analytical expression derived is applied to a real bacterial population (Escherichi coli) and kinetic patterns are theoretically computed. The major findings, expressed roughly, without nuances, are: (i) the concentration of nutrient at the cell membrane,C c, can only be equal to either 0 (for theC s below some threshold valueC *) orC s (forC s〉C *); (ii) the Michaelis-Menten-Monod kinetics observed in experiments is an artifact: the pure (not contaminated by foreign factors) dependence ofc onC s is actually such that the functionc=c(C s) has practically linear increase whenC s〈C *, and is constant,c=c(C *)=const, whenC s〉C *; (iii) the Liebig principle is strictly fulfilled: up to a feasible accuracy of observation, under no circumstances can population growth be limited (controlled) by more than one substrate component—replacement of a limiting component for another one is an instant event rather than a gradual process.

Notes: Abstract We study the equilibrium properties of idiotypically interacting B cell clones in the case where only the differentiation of B cells is affected by idiotypic interactions. Furthermore, we assume that clones may recognize and be stimulated by self antigen in the same fashion as by antiantibodies. For idiotypically interacting pairs of non-autoreactive clones we observe three qualitatively different dynamical regimes. In the first regime, at small antibody production an antibody-free fixed point, the virgin state, is the only attractor of the system. For intermediate antibody production, a symmetric activated state replaces the virgin state as the only attractor of the system. For large antibody production, finally, the symmetric activated state gives way to two asymmetric activated states where one clone suppresses the other clone. If one or both clones in the pair are autoreactive there is no virgin state. However, we still observe the switch from an almost symmetric activated state to two asymmetric activated states. The two asymmetric activated states at high antibody production have profoundly different implications for a self antigen which is recognized by one of the clones of the pair. In the attractor characterized by high autoantibody concentration the self antigen is attacked vigorously by the immune system while in the opposite steady state the tiny amount of autoantibody hardly affects the self antigen. Accordingly, we call the first state the autoimmune state and the second the tolerant state. In the tolerant state the autoreactive clone is down-regulated by its anti-idiotype providing an efficient mechanism to prevent an autoimmune reaction. However, the antibody production required to achieve this anti-idiotypic control of autoantibodies is rather large.

Notes: Abstract It is widely believed, following the work of Connor and Stevens (1971,J. Physiol. Lond. 214, 31–53) that the ability to fire action potentials over a wide frequency range, especially down to very low rates, is due to the transient, potassium A-current (I A). Using a reduction of the classical Hodgkin-Huxley model, we study the effects ofI A on steady firing rate, especially in the near-threshold regime for the onset of firing. A minimum firing rate of zero corresponds to a homoclinic bifurcation of periodic solutions at a critical level of stimulating current. It requires that the membrane's steady-state current-voltage relation be N-shaped rather than monotonic. For experimentally based genericI A parameters, the model does not fire at arbitrarily low rates, although it can for the more atypicalI A parameters given by Connor and Stevens for the crab axon. When theI A inactivation rate is slow, we find that the transient potassium current can mediate more complex firing patterns, such as periodic bursting in some parameter regimes. The number of spikes per burst increases asg A decreases and as inactivation rate decreases. We also study howI A affects properties of transient voltage responses, such as threshold and firing latency for anodal break excitation. We provide mathematical explanations for several of these dynamic behaviors using bifurcation theory and averaging methods.

Notes: Abstract This paper deals with the relative growth of three different fruit tissues. Their morphogenetic periods and the mathematical constraints involved are described, and more precisely, the paper shows an allometric relationship (Y=nX m ) between the widths (X, Y) of the main tissues in stone fruits such as cherries, peaches and prunes. The mathematical relationships between the growth of the mesocarp and of the endocarp of somePrunus fruits are described, and it is proved that before the formation of the embryo, growth is allometric, in agreement with conclusions drawn from some experimental data. However, according to another study, the growth of the mesocarp and of the endocarp are ruled by autocatalytic and monomolecular functions, before as well as after the formation of the embryo. In this case, it is proved that if allometry exits in stone fruits, it can only be anantiometry (m=−1). To solve the dilemma, two main alternatives are proposed and discussed. We conclude that, while allometry is established on reasonable grounds before the formation of the embryo, after the formation of the embryo the mesocarp and endocarp evolve independently since a center for the coordination of growth no longer exists, and each tissue can grow according to its own independent rules.

Notes: Abstract In many organisms, a reliable number of segments is produced even though important properties of the region involved, especially its size at the time of pattern formation, are apparently not specified with sufficient precision. We show that this can be readily accomplished if segmentation occurs through a sequence of bifurcations rather than all at once, and we provide evidence from developmental studies that indicates that this is typically what actually occurs. Our results strongly suggest that where patterns are formed reliably, this generally happens in stages rather than by the setting up in advance of a complete prepattern.

Notes: Abstract Adaptive characteristics of circadian rhythm are based on their capacity to be synchronized by external signals, particularly light signals. The effect of both single and periodic light signals on the electroretinogram (ERG) circadian rhythm in crayfish is studied. In a previous work (Lara-Aparicioet al., Bull math. Biol. 55, 97–110, 1993) we developed a mathematical model simulating the emergence of the ERG circadian rhythm during the ontogeny of the crayfish. In the present work we have tested the familiar wave-shift behaviour of an oscillator with a single limit cycle. Two new facts, not present in a simpler model, now appear, which simulate adequately the experimental results, i.e. the presence of a transient stage and the shape of the perturbed wave which changes according to the characteristics of the external light signals.

Notes: Abstract In the field of biological regulation, models dictated by expreimental work are usually complex networks comprising intertwined feedback loops. In this paper the biological roles of individual positive loops (multistationarity, differentiation) and negative loops (homeostasis, with or without oscillations, buffering of gene dosage effect) are discussed. The relationship between feedback loops and steady states is then clarified, and the problem: “How can one conveniently disentangle complex networks?” is then considered. Initiated long ago, logical descriptions have been generalized from various viewpoints; these developments are briefly discussed. The recent concept of the loop-characteristic state, defined as the logical state located at the level of the thresholds involved in the loop, together with its application, are then presented. Biological applications are also discussed.

Notes: Abstract Trees with a coloration of their leaves have an induced “length” which forms the basis of the widely used maximum parsimony method for reconstructing evolutionary trees in biology. Here we describe five unexpected properties of this length function, including refinements of earlier results.

Notes: Abstract A number of bacterial and viral genes take part in the decision between lysis and lysogenization in temperate bacteriophages. In the lambda case, at least five viral genes (cI, cro, cII, N and cIII) and several bacterial genes are involved. Several attempts have been made to model this complex regulatory network. Our approach is based on a logical method described in the first paper of the series which formalizes the interactions between the elements of a regulatory network in terms of discrete variables, functions and parameters. In this paper two models are described and discussed, the first (two-variable model) focused on cI and cro interactions, the second (four-variable model) considering, in addition, genes cII and N. The treatment presented emphasizes the roles of positive and negative feedback loops and their interactions in the development of the phage. The role of the loops between cI and cro, and of cI on itself (which both have to be positive loops) was discovered earlier; this group's contribution to this aspect mainly deals with the possibility of treating these loops as parts of a more extended network. In contrast, the role of the negative loop of cro on itself had apparently remained unexplained. We realized that this loop buffers the expression of genes cro itself, cII, O and P against the inflation due to the rapid replication of the phage. More generally negative auto-control of a gene appears an efficient way to render its expression insensitive (or less sensitive) to gene dosage, whereas a simple negative control would not provide this result.

Notes: Abstract Cannibalism can have a stabilizing effect in a predator-prey system. Contrary to the intuitive expectation cannibalism of the predator leads to an increase of the standing stocks of both, prey and predator.

Notes: Abstract The bifurcations of a periodically forced predator-prey model (the chemostat model), with a prey feeding on a limiting nutrient, are numerically detected with a continuation technique. Eight bifurcation diagrams are produced (one for each parameter in the model) and shown to be topologically equivalent. These diagrams are also equivalent to those of the most commonly used predator-prey model (the Rosenzweig-McArthur model). Thus, all basic modes of behavior of the two main predator-prey models can be explained by means of a single bifurcation diagram.

Notes: Abstract Concomitant resistance is a tumor growth dynamic which results when the growth of a second tumor implant is inhibited by the presence of the first. Recently, we modeled tumor growth in the presence of a regenerating liver after partial hepatectomy (Michelson and Leith,Bull. Math. Biol. 57, 345–366, 1995), with an interlocking pair of growth control triads to account for the accelerated growth observed in both tissues. We also modeled tumor dormancy and recurrence as a dynamic equilibrium achieved between proliferating and quiescent subpopulations. In this paper those studies are extended to initially model the concomitant resistance case. Two interlocking model systems are proposed. In one an interactive competition between the tumor implants is described, while in the other purely proportional growth inhibition is described. The equilibria and dynamics of each system when the coefficients are held constant are presented for three subcases of model parameters. We show that the dynamic called concomitant resistance can be real or apparent, and that if the model coefficients are held constant, the only way to truly achieve concomitant resistance is by forcing one of the tumors into total quiescence. If this is the true state of the inhibited implant, then a non-constant recruitment signal is required to insure regrowth when the inhibitor mass is excised. We compare these theoretical results to a potential explanation of the phenomenon provided by Prehn (Cancer Res. 53, 3266–3269, 1993).

Notes: Abstract Radiation target theory has been extended to complex biochemical systems. Mathematical analyses are presented for multiple forms of biological active proteins, for the presence of large inhibitors or activators, for compounds which regulate rate or affinity and for multipe-step reactions. Several predictions of these models have been verified experimentally.

Notes: Abstract Aggregation of membrane molecules is a crucial phenomenon in developing organisms, a classic example being the aggregation of post-synaptic receptors during synaptogenesis. Our understanding of the molecular events involved is improving, but most models of the aggregation or concentration process do not address binding events on the molecular level. An exception is the study of diffusion limited aggregation, in which the aggregation process is simulated on a molecular level. In this analysis, however, important physical parameters such as molecular size, diffusion constant and initial density are not addressed. Thus no predictions about the rate at which such aggregates will form is possible. In the present work the model of diffusion limited aggregation is extended to incorporate these parameters and make the corresponding predictions.

Notes: Abstract This paper presents a description of the procedure for building a structured model of a complex pharmacokinetic system on using its transfer function. The example employed is that of the pharmacokinetic system based on gentamicin plasma concentrations after intravenous and intratracheal administration to guinea pigs, describing the pathway of the drug into the systemic circulation after the extravascular injection mentioned. The structured model selected consisted of a submodel of a proportional linear subsystem, two submodels of simple linear dynamic subsystems with time constants of 0.135±0.065 hr (95% I.C.) and 0.052±0.288 hr, submodels of parallel subsystems with time delays of 0.254±0.046 hr and 1.135±0.288 hr, connected in serial. Two estimates of the mean residence time of the total amount of gentamicin in the system, i.e. 0.347 and 0.335 hr, were obtained, based on the system frequency and structured model, respectively. From the methodological point of view, our paper demonstrates the efficiency of combination of modelling in the frequency and in the time domain, designed to facilitate studies of pharmacokinetic systems.

Notes: Abstract In this paper we present an oscillatory neural network composed of two coupled neural oscillators of the Wilson-Cowan type. Each of the oscillators describes the dynamics of average activities of excitatory and inhibitory populations of neurons. The network serves as a model for several possible network architectures. We study how the type and the strength of the connections between the oscillators affect the dynamics of the neural network. We investigate, separately from each other, four possible connection types (excitatory→excitatory, excitatory→inhibitory, inhibitory→excitatory, and inhibitory→inhibitory) and compute the corresponding bifurcation diagrams. In case of weak connections (small strength), the connection of populations of different types lead to periodicin-phase oscillations, while the connection of populations of the same type lead to periodicanti-phase oscillations. For intermediate connection strengths, the networks can enter quasiperiodic or chaotic regimes, and can also exhibit multistability. More generally, our analysis highlights the great diversity of the response of neural networks to a change of the connection strength, for different connection architectures. In the discussion, we address in particular the problem of information coding in the brain using quasiperiodic and chaotic oscillations. In modeling low levels of information processing, we propose that feature binding should be sought as a temporally coherent phase-locking of neural activity. This phase-locking is provided by one or more interacting convergent zones and does not require a central “top level” subcortical circuit (e.g. the septo-hippocampal system). We build a two layer model to show that although the application of a complex stimulus usually leads to different convergent zones with high frequency oscillations, it is nevertheless possible to synchronize these oscillations at a lower frequency level using envelope oscillations. This is interpreted as a feature binding of a complex stimulus.

Notes: Abstract The planktonic and epibenthic crustacean fauna from two sites of the brackish Schlei fjord, Northern Germany, was investigated over a six-month period. Calanoid and cyclopoid copepods were more abundant in lower salinities, whereas, benthic decapods, isopods and amphipods prevailed in the site of higher salinity. Cestodan larvae were found only in spring which may be due to the timing of the respective life-cycles. Parasites of benthic crustaceans, mostly digenean metacercariae but also cestodans, acanthocephalans and nematodes, appeared from spring to late summer. Decreasing salinities caused lower intensities of the most abundant parasite,Maritrema subdolum; only the true brackish-water species among the hosts were more heavily infested than those found in higher salinities. The correlation of parasite size and host size at infestation became apparent. Therefore,Crangon crangon is an optimal host for the largePodocotyle atomon metacercariae. Coevolutive trends between some hosts and parasites are made evident.

Notes: Abstract For the calculation of steep water waves, a Lagrangian method is presented. This makes it easier to derive and understand the complicated non-linear structure of the equations of motion (EOM), for the behaviour of water surfaces. In addition, this formulation offers the possibility to model an EOM which describes water waves with deference to variation in depth.

Notes: Abstract Diel vertical migration of a stable and well-defined population of Nordic krill,Meganyctiphanes norvegica (Crustacea, Euphausiacea) was investigated during eight days in August 1989, in the Läsö-Deep, East of the Danish island Läsö. Net catches with a multi-net (MOCNESS) and measurements with a moored and a shipboard Acoustic Doppler Current Profiler (ADCP) were compared. Backscattered energy as a measure for biomass gave good correlations to the dry weight ofM. norvegica and smaller zooplankton from net catches. Diel migratory patterns matched well, as determined, parallel with both methods. Migratory vertical velocity was determined with ADCP at 2–3 cm sec−1. The potential for the use of ADCPs for biological investigation is discussed. Vertical migration was dependent on environmental parameters. The krill did not cross a temperature barrier of 14°C, although rich food sources were situated beyond it. Differences in salinity did not play a role. Currents were involved in plankton distribution. Light was an important Zeitgeber (synchronizer) and determined the density of the krill aggregations. Feeding behaviour did not interfere with the light-induced migratory pattern of Nordic krill at the Läsö-Deep.

Notes: Abstract The hatching enzyme ofAscidiella aspersa has been characterized as a trypsin-like enzyme. It dissolves the main part of the chorion and renders hatching possible at the end of embryogenesis. In contrast to Knaben's statement, this enzyme is secreted by the embryo itself and not by the test cells.

Notes: Abstract This paper is a review of the present state of knowledge about the ecology of the Dogger Bank, a shallow area in the central southern North Sea. The biological situation in this region is different from other regions in the North Sea; phytoplankton production occurs throughout the year, connected with low periodicity in macrofaunal abundance and condition of fish. Against prevailing opinions, the Dogger Bank, an offshore region, seems to be affected by eutrophication and pollution.

Notes: Abstract The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm3 in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm3. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.

Notes: Abstract Greece, as is known, has a coastline of 17 000 km, and over 2000 small and large islands. As expected, the quest of humankind for new sources of matter and energy has been focussed on the sea, with fishery being its primary interest. A number of philosophers and scientists have been involved in the study of this vast ecosystem since ancient times (Aristotle). The political, social and geographical upheavals witnessed in the Greek area, have, however resulted in bringing all these activities to a halt. The first contemporary research work commenced at the end of the 18th century/beginning of the 19th — with marine flora and fauna as its starting point. The first investigations had, of course, been limited to random collections of marine material done in the frame of international exploratory expeditions. Studies became more systematic by the end of the 19th and beginning of the 20th century, with priority being given to the animal kingdom (fish, molluscs, etc.). Investigation of the marine phytobenthos (macrophyceae, phytoplankton) was to follow. The past 40 years research has been more extensive, not limited only to biogeographical evaluations, but also having expanded to physiological and ecological levels. The relevant institutes of Greek universities have all the while watched and contributed to this effort. Today, this kind of research is being supported by the N.M.R.C., the Center of Marine Research, University of Crete, and two research boats which sail the Greek seas. In the ever-changing world, the study of marine flora and fauna has certainly made great progress; however, there are still two big problems to be faced. The first deals with increasing pollution of the seas, the second, with the difficulties in finding and affording adequate financial resources that would enable a more detailed and complete execution of this research work.

Notes: Abstract A detailed analysis is presented of the main contributions, both local and international, to the fields of oceanography and fishery sciences resulting from exploratory cruises carried out on the continental shelf off Argentina over the last 100 years. The end of the 19th century is chosen as a starting point for this analysis as it marks the beginning of active marine research by Argentinian scientists and an accumulation of information on Antarctic and Subantarctic organisms in foreign journals. Mention is also made of previous contributions derived from the classic expeditions and global circumnavigational voyages during the 18th and 19th centuries. Although the aims of those were not always strictly oceanographic, they rendered significant information to this field of knowledge. In the early years, references arose mainly from the particular geographic situation of the Argentinian shelf, a necessary passage in the navigation routes to the Pacific Ocean, and later on the way to Antarctica. Sources of information are divided into four categories: (a) foreign scientific projects in the area; (b) investigation by Argentinian scientists and research vessels; (c) joint projects between Argentinian and foreign institutions; and (d) contributions from sources other than oceanographic cruises (commercial navigation, maritime weather reports, satellite images, etc.). The analysis includes an updated and classified bibliographical list of the main contributions to the fields of oceanography and fishery sciences derived from those sources, published either in international or local journals or appearing as technical and internal reports. The motivations, objectives and main achievements of foreign surveys and programmes in the area and their impact on local scientific progress are discussed. The early sixties mark a turning point in the evolution of international research in the area. The creation of biological stations along the Argentinian coast, and the support given to the pooling of human resources set the basis for the development of bilateral programmes. Similar progress in Brazil and Uruguay led to the outgrowth of regional activities. Joint scientific efforts described in this analysis include the programmes carried out by the research vessels of Germany (“Walther Herwig”, “Meteor”), Japan (“Kaiyo Maru”, “Orient Maru”, “Shinkai Maru”), Poland (“Professor Siedlecki”), Russia (“Evrika”, “Dimitry Stefanov”) and the USA (“Vema”, “Atlantis II”), the achievements of which are a landmark in the evolution of marine science in the aea.

Notes: Abstract Juvenile mud snailsHydrobia ulvae disperse by floating at the water surface in summer. The routes of dispersal are determined by the hydrography of the specific area and can be successfully predicted by a hydrographic model. Along these routes, juveniles may aggregate in temporary “satellite” sites. Turnover of organisms was high at these sites. On average, an individual only stayed for 2 days in June and July, and a few hours in August. Consequently, abundance may vary by an order of magnitude within a few days. In August, the satellite sites were depopulated again, presumably due to behavioural changes. Because of the high mobility, caution is advised when including juvenile mud snails in descriptive or experimental field studies. High turnover rates of individuals in the sediment have also been recorded for juvenile bivalves and various meiofaunal taxa. The value of single-site sampling may therefore be questioned with respect to migrating benthic species. Instead, a mapping of resident and satellite subpopulations is recommended.

Notes: Abstract A statistical analysis was performed to determine environmental factors of significant influence on the mesozooplankton in the northern Wadden Sea of Sylt (German Bight) in 1991. The total mesozooplankton (〉76 μm) was significantly correlated with water temperature as was the case with the calanoid copepodAcartia sp.;Pseudo- andParacalanus sp. were influenced by the amount of rainfall, whereas the amount of the meroplanktonic larvae of the cirripedia was related to the amount of particulate organic nitrogen in the water. A comparison of the years 1984 and 1991 demonstrates the positive effect of temperature on the copepod speciesAcartia sp. in summer.

Notes: Abstract Visakhapatnam Harbour, a semi-enclosed water body on the east coast of India, is subject to a high degree of pollution caused by industrial and urban wastes. Studies carried out during the last twenty years or so at 6 selected stations in the harbour revealed appreciable hydrographic and biotic changes. Over the years, the concentration of nitrites (max. 5 mg/l) and phosphates (9.6 mg/l) has increased. Dissolved oxygen registered all-time-high values (max. 21.6 mg/l) caused by periodic outbursts of phytoplankton, notably,Skeletonema costatum and other species. Benthic conditions have also changed and only certain pollution-tolerant species (e.g.Capitella capitata) inhabited the bottom sediments that contained a heavy load (2.5%) of organic matter. In the harbour, increased pollution led to the disappearence of stenoecious species and their replacement with other forms known for their tolerance to pollution. The paper describes the major changes which have occurred in water quality and organisms in the harbour as a result of pollution increase during the last two decades.

Notes: Abstract Marine biological monitoring programmes frequently attempt to determine “safe” levels of contamination, based on assumptions about the assimilative capacity of the environment. This paper argues that such assumptions lack scientific rigour, and do not form the basis upon which a precautionary policy can be built. It notes the problems associated with assessing toxicological effects, but centres its attention on the crucial (yet far less discussed) weaknesses in theoretical ecology that make it extremely unlikely that biological monitoring can determine safe levels of contamination that leave ecosystems unaffected. It is argued that many marine biologists, if pressed, would concede these shortcomings but believe that, in the face of the technical difficulties and high costs of pollution prevention, we have no choice but to use such methods. This paper argues, with examples, that pollution prevention, often with considerable economic savings, is becoming a reality for even the most problematic substances. The difficulty is that the development of “clean production” methods lie outside the sphere of interest of those carrying out monitoring, so that measures that attempt to determine safe levels of contamination continue to be advocated. This gulf needs to be bridged so that the continuation of monitoring programmes that are part of dilute and disperse policies become regarded as inappropriate, indeed unethical. The paper concludes that this does not mean the end of marine monitoring. Instead, reliable methods for assessing physical levels of contamination will be required to determine whether the reduction targets set—as part of the introduction of clean production—are being met. Formidable difficulties will remain, requiring a precautious approach. Nevertheless, monitoring will no longer carry the burden of attempting to demonstrate that a particular level of environmental contamination is safe, which is currently destroying its scientific credibility.

Notes: Abstract In a preparation of isolated gills of the shore crabCarcinus mediterraneus perfused with dilute sea water (pH 8.1, 200 mM Na+) which was identical to the bathing solution of the gill, acidification of the collected perfusate was observed. Acidification was not affected by 10−4 M EIPA (5-[N-ethyl-N-isopropyl]amiloride), a strong inhibitor of Na+/H+ exchange. However, in the presence of 10−4 M acetazolamide, acidification was greatly blocked. The significant decrease of the acid load of the perfusate is considered to be a result of inhibition of the branchial intracellular carbonic anhydrase catalyzing the formation of H+ ions.

Notes: Abstract The activity of microorganisms was investigated in sediment samples of the Norwegian Sognefjord at a 1260 m depth. The enzymatic potential (measured, using the cleavage of fluoresceindiacetate FDA) ranged between 11 and 29 nmol FDA cm−3 h−1. LabeledAnacystis sp. (Cyanobacteria) were degraded (measured as liberation of14C-labeled CO2) at a rate of 0.67–1.24% day−1. The assays were run at 1 atm and at 126 atm pressure. In both cases, activity was higher when samples were incubated under 1 atm than under simulated in-situ conditions. This indicates that the sediment community of the fjord is adapted only to a limited extent to the elevated pressure at the bottom. The results are compared and discussed with data from other deep marine environments.

Notes: Abstract Looking back from the 1990s it seems natural to view the work done in the Biologische Anstalt Helgoland by Friedrich Heincke and his colleagues, beginning in 1892, as marine ecology or marine biology, and that done in Kiel, under Victor Hensen and Karl Brandt, as biological oceanography. But historical analysis shows this view to be untenable. Biological oceanography, as a research category and a profession, does not appear until at least the 1950's. In the German tradition of marine research, “Ozeanographie”, originating in 19th century physical geography, did not include the biological sciences. The categories “Meereskunde” and “Meeresforschung” covered all aspects of marine research in Germany from the 1890's to the present day. “Meeresbiologie” like that of Brandt, Heincke, and other German marine scientists, fitted comfortably into these. But in North America no such satisfactory professional or definitional structure existed before the late 1950's. G. A. Riley, one of the first biological oceanographers, fought against descriptive, nonquantitative American ecology. In 1951 he described biological oceanography as the “ecology of marine populations”, linking it with quantitative population ecology in the U.S.A. By the end of the 1960's the U.S. National Science Foundation had recognized biological oceanography as a research area supported separately from marine biology. There was no need for the category “biological oceanography” in German marine science because its subject matter lay under the umbrella of “Meereskunde” or “Meeresforschung”. But in North America, biological oceanography — a fundamental fusion of physics and chemistry with marine biology — was created to give this marine science a status higher than that of the conceptually overloaded ecological sciences. The sociologists Durkheim and Mauss claimed in 1903 that, “the classification of things reproduces the classification of men”; similarly, in science, the classification of professions reproduces the status that their practitioners hope to achieve.

Notes: Abstract Jassa falcata andCorophium insidiosum are epifaunal tube-building marine amphipods, whose niches overlap in habitat and food requirements. Laboratory experiments were conducted to study the influence of the quality of different available particulate substrates on settlement and tube-building behaviour of these two amphipod species. Our experiments suggest thatC. insidiosum is less specialized in this respect thanJ. falcata. C. insidiosum is able to use organic materials for tube-building such as artificial (Ulva spec. powder) or mixed natural detritus as well as inorganic material (coarse sand); whereasJ. falcata utilizes organic materials, but sand only to a very limited extent.

Notes: Abstract A study of research funding at Memorial University's Marine Sciences Research Laboratory shows that true costs far exceed support from grants and contracts alone. Research grant levels have to be matched by a similar level of support for infrastructure, and other university-supplied support (mostly salaries) may amount to twice that supplied by grants. Faced with declining external support for general infrastructure, universities can ill afford to become involved in scientific mega-projects. There is little evidence that increased funding enhances productivity.

Notes: Abstract Predictive ecosystem research needs a pluralistic approach. Retrospective studies reveal the initial causes of ongoing ecological change. In the Wadden Sea, inherent ecosystem stability may be falsely assumed, because the effects of modern coastal architecture and of anthropogenic eutrophication to some extent complement each other. Expected environmental changes often have corresponding phases in the past which may serve as a model to predict ecological implications. Historically, quantitative ecology entered the Wadden Sea, via fisheries research, from the oceanic side. Quantified material fluxes may reveal imbalances which are indicative of the rough direction of ecosystem change. For ecosystem research to contribute to the maintenance of the Wadden Sea as a centre of coastal organisms, quantitative knowledge of resources and ecosystem metabolism must be supplemented by qualitative knowledge of habitat requirements and species interdependences. Qualitative ecology entered the Wadden Sea from the landward side. Extending this approach to anticipatory field experiments may help to predict ecological changes at the species level.

Notes: Abstract In search of means to reduce the by-catch of juvenile flatfish in the shrimp fishery, vibrations and changes in current velocity caused by shrimp trawls were investigated in the field and in the laboratory. Buried as well as emerged shrimps (Crangon crangon) exhibit tailflips 5–10 cm before being touched by the rollers of a shrimp gear approaching them at a speed of 0.5 m·sec−1, as was revealed by slow motion video recordings in aquaria under artificial light. Hence, the signal effective in triggering escape must be attenuated strongly with increasing distance. Sediment vibration, commonly assumed to be an important signal in triggering escape of shrimps, was found to decrease by a factor 100·m−1. Signals from the rollers of a commercial shrimp gear in operation (towing speed 1 m·sec−1) were directly recorded with an accelerometer. Their frequency ranged from 50 to 500 Hz and reached an acceleration of 40 m·sec−2 on soft bottom or up to 100 m·sec−2 on hard substrate. Accelerometers, which had been buried right at the surface of a tidal sand flat during low tide, produced only one sharp signal of 100 Hz with an acceleration of 24 m·sec−2, when a shrimp gear swept them on the submerged tidal flats. However, in aquaria short sinusoidal signals (〈5 m·sec−2; 20 to 300 Hz) made buried shrimps and flatfish (Pleuronectes platessa, Solea solea, Microstomus kitt) hide rather than flee. The vibrations recorded directly at the rollers and the underlying jolting movements of the rollers induce corresponding pulses in the water surrounding the rollers in a layer of approximately 10–15 cm. Similar water displacement of high acceleration was experimentally produced by a spring loaded transparent lucite piston (7 cm in diameter) fitted to an accelerometer. Accelerating this piston (12–116 m·sec−2, 50–200 Hz range) from 5 cm above towards the shrimp produced escape responses in up to 94% of the tests. Arthropods are known to perceive medium displacement rather than pressure. Hence, strong and rapidly rising water currents caused by the rollers rather than sediment vibration are assumed to mainly trigger the escape reaction, which makesCrangon accessible to the gear.

Notes: Abstract General features of benthos communities of tropical tidal flats are defined from northeast Australia, based on surveys from 1988 to 1991 in Hinchinbrook Channel and in the Haughton River estuary. A zonation of benthic communities is described. Total abundances for macrofauna averaged 31 individuals 200 cm−2, mesofauna (defined as infauna smaller than 0.5 mm and retained on a 0.25 mm sieve) averaged 16 individuals 10 cm−2 and meiofauna averaged 231 individuals 5 cm−2. The two study sites were similar in their abundance structures, but species due to a higher diversity of polychaeta in the Channel (120 species, H′=3.80 vs. 29 species and H′=1.78 in the Haughton estuary). Species densities were comparable at both sites and rather low (6 species 177 cm−2, 2–7 species 10 cm−2 and 5 meiobenthic Plathelminth species 5 cm−2). Over 50% of the species encountered were represented by less than three individuals. Deposit feeders, dominated the assemblages both in terms of individuals as well as species numbers. Tropical tidal flats are compared with their temperate counterparts and approaches for future research in tropical benthos communities are recommended.

Notes: Abstract Looking forward on this occasion, rather than reviewing the past 100 years, it appears that 100 years hence, we will have to manage the environment worldwide like a global garden. How will the ecological knowledge necessary for sound management be acquired? Drawing especially on concepts about the plankton of the open North Sea and on unresolved issues of understanding, questions will be raised about research direction and organization that will need to be answered long before the next 100 years have passed.

Notes: Abstract Coherent assemblages of marine benthic species have been recognized from the early twentieth century, and the classical papers of Petersen (1914, 1918) were based on studies of limited areas in the North Sea. In 1986, a synoptic survey of the North Sea north to 57°N was undertaken by a group of ten laboratories from seven North Sea countries. The results of this survey have recently been published (Heip et al., 1992a, b; Künitzer et al., 1992; Huys et al., 1992), and some of the results are summarized in this paper. The analysis of the macrofauna is based on slightly more than 700 taxa. In general, the North Sea macrofauna consists of northern species extending south to the northern margins of the Dogger Bank, and southern species extending north to the 100 m depth line. The central North Sea is an area of overlap of southern and northern species, especially around the 70 m depth contour. Consistent groupings of species are recognized that were summarized in seven faunal groupings. Macrofaunal body weight, density and diversity increase linearly towards the north. Macrofaunal biomass for the whole area averages 7 g adwt. m−2 and decreases from south to north. Distribution patterns and trends within the meiofauna were very different. Nematodes, which are the dominant taxon overall, are least abundant in the sandy sediments of the Southern Bight, then increase to a maximum around 53° 30′ N and slowly decrease again towards the north. Copepod density and diversity are highest in the Southern Bight, due to the presence of many interstitial species. A large number of species new to science were recorded by the North Sea Benthos Survey and about 1500 species are expected to occur. Copepods show very distinct assemblages according to water depth and sediment type. The contrasting patterns in latitudinal gradients of body weight and number of species of macro- and meiofauna can be only partially explained. Latitude and sediment characteristics, such as grain size and content in plant pigments, and water depth, determine part of the variance in species composition, density and biomass of the benthic fauna, but the patterns that are observed are different for different benthic groups, requiring careful consideration as to their use in biological monitoring procedures. Distributions are related to current patterns in the North Sea, annual temperature variations and availability of food. However, large parts of the variance in many parameters remain unexplained.

Notes: Abstract The phytoplankton succession and related abiotic variables were investigated within the frame of a monitoring programme. Results from 1985 to 1991 are presented. For the prymnesiophytePhaeocystis globosa, an increase in the maximum annual abundance was observed. The appearance of this species in the phytoplankton succession followed an annually recurrent pattern. Among the starting conditions for the bloom, a coincidence with the annual DIN/P maximum was most obvious. Quantitatively, temperature and salinity showed the lowest variability at the onset of the blooms. Nutrient uptake during the increasing phase of the bloom appeared to affect nitrate concentrations more significantly than those of ammonia and phosphate.

Notes: Abstract The institute in Rovinj was founded in 1891 as the field station of the Berlin Aquarium. It soon gained in scientific importance. From 1911, it was governed by various scientific bodies, such as the ‘Kaiser-Wilhelm-Gesellschaft zur Förderung der Wissenschaften’, the ‘Reale Comitato Talassografico Italiano’, and the ‘Jugoslavenska Akademija znanosti i umjetnosti’. At present, it is a department of the ‘Ruđer Bošković’ Institute, called the ‘Center for Marine Research Rovinj’. In the past hundred years, the Rovinj station experienced several ascents and declines in its development: both in the First and Second World Wars the station's scientific equipment, research vessels, library and reference collections were dispersed, and from 1945–1948 the station was closed. But in “happier” periods, rich support by the state and international bodies favoured the increase in research facilities and promoted interest among visiting scientists. The station has always been involved in studies of the Adriatic Sea, especially in its northern part. It contributed much to general knowledge of oceanography, of the physics and chemistry of the sea, but its paramount contribution is to various disciplines of marine biological sciences. Applied research, however, was most oriented to fisheries biology, especially shellfish culture, to resource studies, and, recently, to toxicology, bacteriology, eutrophication and pollution monitoring. The international approach in science and applied research was always favoured. At present, the Center is well equipped for complex coastal and offshore field- and laboratory research, and maintains facilities for graduate and postgraduate teaching. Scientific dissemination is also promoted by the public aquarium and professional meetings.

Notes: Abstract Seven research suggestions are discussed: the phenomenon of the rare species, the life conditions of meiofauna in suboxic sediment layers, the part-time dormancy of animals and bacteria in the sediment, the importance of lateral advection for the flux of organic matter to the benthos, the selection of sites representative of larger North Sea regions, the selection of monitoring stations, and the importance of viruses, bacteria and other parasites for the North Sea ecosystem.

Notes: Abstract Most fishery products consist of muscle tissue from fish and invertebrates. Differences in the molecular structure and in metabolism of muscles can be utilized to characterize and identify various seafood. Creatine and arginine were found to be useful for the differentiation between imitation crab/shrimp meat and real crustacean meat. Octopine served as an indicator for the meat of cephalopods and mussels. In order to identify the animal species of a fishery product, several electrophoretic methods were used. It depended on the type of product, whether sarcoplasmic or myofibrillar proteins were better suited. Raw products were best analysed by isoelectric focusing of sarcoplasmic proteins. Two types of sarcoplasmic calcium-binding proteins, parvalbumins of fish and soluble calcium-binding proteins of invertebrates, were especially useful for species identification. Due to their thermal stability, these proteins gave species-specific patterns for cooked products, too. Two other techniques were also investigated: urea gel isoelectric focusing, and sodium dodecyl sulphate — polyacrylamide gel electrophoresis. These methods were applied in the analysis of products where the sarcoplasmic proteins had been removed by washing steps, i.e. imitation crab meat made from surimi, and of other raw and cooked products. The myosin light chains gave protein patterns that were characteristic for many species. Paramyosin, which is absent from vertebrate muscle, indicated the presence of mollusc muscle. It was shown that the determination, of arginine kinase activity enabled differentiation between raw fish muscle and invertebrate muscles.

Notes: Abstract We compared the reproductive output, local recruitment rates and survival rates of 1 year old Coal Tit females breeding only once („group 1“) with the corresponding values of 1 year old females breeding twice („group 2“). One year old females which failed first or second broods were excluded. Survival was estimated by the local recovery rate of females during the next breeding season. Our data do not fit with the „cost of reproduction hypothesis“ as females with significantly higher reproductive output and recruitment („group 2“) did not show lower survival. We even found a significantly positive correlation between production of a second brood and recovery rate the next year.

Notes: Abstract In 1991 and 1992 Common and Arctic Terns differed in chick-feeding and chick-rearing strategies. Arctic Terns favoured smaller prey, primarily crustaceans, for feeding their chicks than did Common Terns. Consequently, Arctic Tern feeding rates were higher. The influence of the tide on food parameters was greater in Arctic Terns. In both years breeding success was better in Common Terns.

Notes: Abstract The scheme of macrozoobenthos research development in the southern region of the Baltic Proper is presented here. In the course of a 120-year-long investigation cycle, four different, partly overlapping periods can be distinguished: qualitative investigations, quantitative distribution studies, biomass investigations, and regular monitoring of zoobenthos.

Notes: Abstract The “Institut für Meereskunde” (IfM) in Berlin, founded in 1900, first took up marine biology as a section of its museum, in which emphasis was placed on the environment and the components of local ecosystems rather than on extraordinary species. The first joint research project of the Biologische Anstalt Helgoland (BAH) and the IfM in Berlin was instigated by the physicist A. Merz; it included several time-series of hydrographical and biological samples at fixed stations (light vessels) in the German Bight. When plans were made to establish a biological station in Constantinople during World War I, the colleagues in Berlin tried to change it into an integrated physicalbiological station, in which biological research would concentrate on revealing the laws of nature rather than simply describing the biosphere. During the recession after the war, the Prussian government was anxious to unite both institutions in order to save money. However, Mielck of the BAH succeeded in preventing the take-over by the Institute in Berlin. The relation between the two institutes stayed cool up to the destruction of the latter in 1945.

Notes: Abstract Despite the fact that many marine fungi, including phycomycetes, yeasts, ascomycetes and hyphomycetes, have been recorded from living and/or dead phaeophytes, only a few of these have been shown to be capable of degrading alginic acid or alginates. The degradation is achieved by the action of an exoenzyme complex, comprising alginate lyase, as well as alginate hydrolase activities. The latter was detected only recently by the authors. In this study, the growth of two marine sodiumalginate-degrading deuteromycetes,Asteromyces cruciatus andDendryphiella salina, was investigated, and the assimilation efficiency of sodiumalginate and its uronic acid degradation products, respectively, was estimated from the economic coefficient (E). E is calculated from the mycelial dry weight, divided by the weight of substrate consumed for this production. The economic coefficient forA. cruciatus was 48.6%, and that ofD. salina 38.9%. This indicates that the former species uses the alginate degradation products more efficiently than the latter. The observed E-values for the marine deuteromycetes agree with those from other fungi, e.g. terrestrial species. In general, it is concluded that the marine fungi appear to play a more important role in kelp-based ecosystems than was realized previously.

Notes: Abstract There are many signals that different human activities affect the marine ecosystem on local and sometimes regional scales. There is evidence that in the Dutch sector of the North Sea at least 25 species have decreased tremendously in numbers or have totally disappeared. But what has caused their disappearance: fisheries, pollution, eutrophication, climatic changes, or a combination of causes? On the Dutch Continental Shelf, the fisheries are now so intensive that every square metre is trawled, on an average, once to twice a year. Furthermore, it has been shown that trawling causes direct damage to the marine ecosystem. This indicates that the “natural” North Sea ecosystem we are studying is already a heavily influenced system. And what is the value of data on the diversity and production of benthic animals, if the research area has been raked by beamtrawl gear an unknown amount of times before sampling? To be able to study the natural trends in the marine ecosystem, or to answer the question which human activity has most influenced the ecosystem, there is an absolute and immediate need for protected areas to be established. The size of the protected areas must be determined by the behaviour of that species characteristic for the area. In such areas, where fisheries and local pollution would be forbidden or very limited, scientific research into the species composition and age distribution of different populations should be carried out and trends should be established.

Notes: Abstract Oceanography and marine ecology have a considerable history in the use of computers for modeling both physical and ecological processes. With increasing stress on the marine environment due to human activities such as fisheries and numerous forms of pollution, the analysis of marine problems must increasingly and jointly consider physical, ecological and socio-economic aspects in a broader systems framework that transcends more traditional disciplinary boundaries. This often introduces difficult-to-quantify, “soft” elements, such as values and perceptions, into formal analysis. Thus, the problem domain combines a solid foundation in the physical sciences, with strong elements of ecological, socio-economic and political considerations. At the same time, the domain is also characterized by both a very large volume of some data, and an extremely datapoor situation for other variables, as well as a very high degree of uncertainty, partly due to the temporal and spatial heterogeneity of the marine environment. Consequently, marine systems analysis and management require tools that can integrate these diverse aspects into efficient information systems that can support research as well as planning and also policy- and decisionmaking processes. Supporting scientific research, as well as decision-making processes and the diverse groups and actors involved, requires better access and direct understanding of the information basis as well as easy-to-use, but powerful tools for analysis. Advanced information technology provides the tools to design and implement smart software where, in a broad sense, the emphasis is on the man-machine interface. Symbolic and analogous, graphical interaction, visual representation of problems, integrated data sources, and built-in domain knowledge can effectively support users of complex and complicated software systems. Integration, interaction, visualization and intelligence are key concepts that are discussed in detail, using an operational software example of a coastal water quality model. The model comprises components of a geographical information and mapping system, data bases, dynamic simulation models, and an integrated expert system. An interactive graphical user interface, dynamic visualization of model results, and a hyper-text-based help-and-explain system illustrate some of the features of new and powerful software tools for marine systems analysis and modeling.

Notes: Abstract The paper reports on levels of heavy metals in some organisms from the eastern Adriatic coast and polluted areas near a big urban centre (Split area). Surprisingly high Hg and MeHg concentrations were found in sea bream (Pagellus erythrinus) and striped mullet (Mullus barbatus) from the south-eastern part of the Adriatic. The reason for the high levels are probably geochemical anomalies. Studies of total and organic mercury content in bivalves have also shown that the gills and hepatopancreas had high levels of accumulated mercury. Our results have shown that fish contain significantly higher concentrations of MeHg than mussel. High concentrations of these elements in fish may be a consequence of the methylation process in the visceral organs. Bacterial activity in the intestinal contents is most likely to be responsible for this methylation (Rudd et al., 1980).