ALBERT

Notes: SUMMARY. 1. The behavioural responses of six species of British freshwater gastropods to chemical gradients of short chain carboxylic acids (C-2 to C-5, C-8) and maltose were investigated by means of diffusion olfactometers.2. The species were ranked as follows on the basis of the number of significant behavioural responses to the test chemicals: Lymnaea peregra 〉 Planorbis contortus 〉 Physa fontinalis 〉 Planorbis planorbis 〉 Bithynia tentaculata 〉 Planorbis vortex. These differences were not a result of differences in activity but reflect real differences in ehemoreception.3. Propanoate (C-3) was a significant attractant or arrestant to five snail species, C-4, C-8 and maltose to four species and C-5 to three species. Acetate (C-2) was a significant attractant to L. peregra and P. fontinalis but it was the only acid to act as a repellent, to P. planorbis and B. tentaculata.4. Lymnaea peregra continued to respond to repeated butanoate application. Response levels could be enhanced by increasing concentration (minimum thresholds 10-4M to 10−5 M), pH (above 6) and food deprivation.5. The ecological relevance of the results are discussed with particular reference to the distributional patterns of the chemicals and snails and the feeding niches of the latter.

Notes: SUMMARY. 1. The behavioural responses of the freshwater pulmonate snail Biomphalaria glabrata to homogenates of various aquatic macrophytes were investigated with the aid of diffusion olfactometers.2. Of the eleven species studied, three lacked any attractants or arrestants, two contained weak arrestants, and three induced strong repellent effects. Only two, Apium nodiflorum and Lemna paucicostata, induced significant attractant and arrestant effects comparable to those obtained with lettuce (Lactuca sativa) controls.3. Decaying Lemna paucicostata homogenate proved to be a significantly stronger attractant and arrestant than fresh homogenate. Evidence is given that these effects are mainly due to low molecular weight compounds (〈1000 mol. wt) of which the major end products of microbial decomposition, short chain carboxylic acids (C2-C5), are likely to be the most important. However, as carboxylic acids account for only a fraction of the total response, other low and high molecular weight compounds are also implicated.4. The ecological relevance of these results is discussed with particular reference to the hypothesis that the relationship between the snails and macrophytes is essentially mutualistic.

Notes: 1. The results of limnological studies on a small, 35-ha, triangular man-made lake and a small adjacent fish pond in the coastal savanna of Ghana are described.2. The lake, which has a renewal time of approximately 0.96 years, is subject to large, predictable seasonal changes. Water volume and surface area rapidly reach maximum values in the wet season from April to June despite the low runoff values which average only 1.2% of the precipitation. Minimum values occur in the dry season when up to 76% of the lake area may be exposed. Most of the water is lost by evaporation which may amount to 193 cm annually.3. The annual cycle in water temperature follows that in solar radiation with peaks towards the end of the dry season in March to April and deep troughs in the wet season from April to June. During the dry season the water column is characterized by greater stability, a higher degree of stratification, and a much higher amplitude of diurnal temperature change (4-5°C) than in the wet season (1°C). Isothermal conditions tend to be approached nocturnally and even during the day in the wet season.4. The ionic content of the water is low and dominated by bicarbonate, sodium, silica and iron. During the wet season flood water results in a decline in conductivity from 214 to 30 μmhos/cm2, a decrease in pH and transparency, and an increase in oxidizable organic material. Except for the conductivity these values return to normal in about 6 weeks as a result of rapid decomposition of allochthonous materials.5. The oxygen pulse is strong and photosynthetic activity by phytoplankton high during the dry season whereas in the wet season the converse is true. As a result of the low concentration of organic carbon (0.10–0.35%) in the sediments their oxygen demands are low. Consequently, dissolved oxygen values near the sediment are relatively high and oxygen stratification poorly-developed. Most of the organic carbon appears to be recycled in the water column rather than in the sediments as is generally the case in tropical ecosystems.6. Rooted vegetation became permanently established in the fish pond but not i n the lake itself. Emergent and floating vegetation which grows profusely in the draw-down area in the wet season is for the most part exported from the system by wind and biological agencies and, therefore, contributes little to the energy and mineral budgets of the lake. Primary production in the water column is mainly by Myxophyceae and Bacillariophyceae and is low during the dry season (1.35 gC/m2/day) and very low in the wet season. Possible reasons for the low level of primary production are discussed.

Notes: SUMMARY. 1. The effects of grazing by Lymnaca peregra and Planorbis planorbis on Ceratophyllum demersum epiphyton were investigated under simulated natural conditions.2. Grazing resulted in significant reductions in algal cell densities, number of algal taxa and in diversity. Grazing did not influence equi-tabilily values.3. The use of Ivlev's Electivity index demonstrated positive and negative selection by feeding snails for large, pedunculate, and small, adnate algae, respectively.4. Inoculation of artificial surfaces revealed that 61.1% and 62.5% of the algal taxa presenl in the diet of L. peregra and P. planorbis, respectively (mainly the smaller species), were able to survive passage through the gut, resettle and grow.5. The results are discussed with particular reference to the survival strategies available to the epiphytes, and the possible mutual benefits which algae and snails may derive from coexistence.

Notes: SUMMARY. 〈list xml:id="l1" style="custom"〉1Samples of two species of aquatic macrophytes, Lemna paucicostata and Ceratophyllum demersum, with which snail hosts of schistosomes are commonly associated, were homogenized, together with their epiphytic flora, and allowed to decompose in closed systems for up to 42 days.2After 10 days of incubation it was found that populations of rod and coccoid shaped bacteria had greatly increased. Fermentation proceeded only to the acid forming stage and no methane was produced.3Despite the differences in the morphologies, habitats and epiphytic flora of the two species, it was found that the short chain carboxylic acids, acetate, propanoate, butanoate and hydrogen were the major end products of microbial decomposition in both cases. There was also some oxygen production from photosynthetically active zones within the homogenates. Most of the accumulation profiles for the acids conformed to logistic growth curves, whereas the hydrogen values fluctuated.4The reasons for the biochemical changes, the differences between the patterns of decomposition in Lemna and Ceraiophyllum. and the ecological relevance of the results to the plants, micro-organisms and the snails are discussed.

Notes: Gamma irradiation of Trichinella spiralis-infected pork with a dose of 15 to 30 krad blocks maturation of ingested larvae in the host gut and prevents production of larval progeny. Experiments with freshly-slaughtered (prerigor) hog carcasses indicate that larvae distributed throughout the skeletal muscles have similar radiosensitivities. Neither the age of the encysted muscle larvae nor vacuum packaging of the meat significantly affected this radiosensitivity. Postirradiation holding of irradiated meat leads to little if any recovery of trichina viability. The data indicate that 30 krad cesium-137 gamma radiation can be delivered to split market-weight hog carcasses with acceptable uniformity, and that under all conditions tested such a dose can provide a substantial margin of safety for human consumption of heavily infected meat.

Notes: 1. Although the mass of dissolved organic matter (DOM) often exceeds that of living organisms in freshwaters, little is known about the roles of its constituent molecules as sources of energy and information for aquatic organisms. In the present review attention is focused on free amino acids (FAA) and humic substances (HS) as examples of labile and refractory components within DOM.2. The following questions are addressed. (i) What are spatiotemporal patterns in the distribution of DOM, HS and FAA? (ii) What are the origins of the components of DOM and how are their concentrations regulated? (iii) What is the significance of the spatial and temporal distributional patterns of DOM, HS and FAA to detritivorous invertebrates and other organisms associated with them? (iv) What is the relevance of DOM to the food web concept and to the biochemical ecology of freshwater ecosystems?3. Concentrations of DOM, FAA and HS within lentic ecosystems are ranked as follows: Sediment pore water 〉 Air–water interface 〉 Midwater column. Comparisons between water bodies show that the concentrations of labile constituents of DOM, such as FAA, are usually positively correlated with base cations, nutrients and biological activity. In contrast, HS concentrations are negatively correlated with base cations or nutrients but positively correlated with the rate of biological degradation (the maximum values occurring in the autumn). The FAA : HS ratios might serve therefore as an indicator of the potential productivity of a water body.4. External sources of DOM in general, and FAA and HS in particular, include rainwater, windborne material, surface flow and groundwater. The relative importance of these allochthonous sources of DOM decreases along the length of lotic ecosystems and also with increase in size of lentic ecosystems. Internal sources of FAA and HS include synthesis or polymerization from existing organic matter, degradation of organic matter and release from both living and dead organisms. The net accumulation of DOM released by living bacteria, phytoplankton, epilithon, macrophytes and invertebrates is much reduced due to heterotrophic uptake. Hence, most of the allochthonous DOM in freshwater originates from dead organic matter deposited on the sediment. Phytoplankton-dominated ecosystems may, however, differ, as most of their DOM may be recycled within the water column.5. The factors that determine the external concentrations of DOM, FAA and HS are discussed. Evidence is cited in support of the following testable hypotheses. (i) The rates of production of DOM components will be favoured by increasing base cation and nutrient concentrations. (ii) Colloidal clay, base cations, biopolymers and living organisms, particularly bacteria, facilitate the removal of HS. Consequently, base-rich eutrophic waters tend to have lower HS concentrations than oligotrophic, base-deficient waters. (iii) As a result of higher productivity and selective removal of FAA, eutrophic waters tend to have higher FAA concentrations than those that are oligotrophic.6. Labile DOM components, such as FAA, act as sources of information for aquatic organisms. More research is needed in this field. There is a consensus that DOM acts as an important source of energy for aquatic bacteria, thus forming the microbial loop. However, higher eukaryotic organisms also utilize DOM, including components released by bacteria and plants as metabolic end-products and photoassimilates, respectively. As a result, these DOM components may be more important as food for macrodecomposers than the microdecomposers themselves. HS may also benefit aquatic organisms by promoting their growth and protecting them from inimical forces. Conversely, the removal of photons and the release of toxins by HS may be detrimental to aquatic organisms.7. It is concluded that the central dogma of the foodweb, and its implicit assumption that the energy flow in aquatic ecosystems can be quantified solely by measuring rates of photosynthesis, ingestion of solid food and its digestion by higher organisms, is invalid. To extend our understanding of the role of DOM as a source of nutrition and information to aquatic organisms it is suggested that the subject should be studied within the context of ‘modules’ which have the following properties: (i) the components have co-evolved; (ii) the more vulnerable components will have protective mechanisms; (iii) the components will derive mutual benefits from co-existence; (iv) sedentary components will release kairomonal attractants or developmental primers; (v) living components will exchange energy and information; (vi) the module will collapse following the removal of strongly interactive keystone species. An example of a three-component, three-subset module, is provided by tubificid worms, epilithic bacteria and algae. A more complex module consisting of pulmonate snails, associated macrophytes, their epiphytic bacteria and algae has four components and six subsets. The elucidation of the interactive mechanisms within such modules demands an interdisciplinary approach, involving microbiology, biochemistry and behavioural biology.