ALBERT

Description: A study on cod egg mortality was carried out in the Bornholm Basin (southern central Baltic Sea) toward the end of July 1996. An initial egg aggregation marked by a satellite-tracked drifter buoy was sampled repeatedly over an 11-day period; profiles of temperature, salinity and dissolved oxygen were concurrently recorded. Three replicate estimates of mortality were obtained for each pair of subsequent developmental stages from newly spawned eggs to early larvae. A consistent pattern of stage-specific mortality coincided well with previous experimental observations. Average daily mortality rates were 7.2% (eggs IA/IB), 38.7% (eggs (IB/II), 25.6% (eggs II/III), 40.0% (eggs III/IV), and 42.3% (eggs IV/early larvae). The cumulative mortality until hatch amounted to 99.9%. Results from hydrodynamic modelling, however, indicated that the drifter's trajectory was influenced by wind stress. Hence, the mortality rates might be biased despite the short sampling intervals; a modification of the sampling design is recommended for future studies.

Description: Recent seismic field work has revealed high lower-crustal velocities under Ninetyeast Ridge, Indian Ocean, indicating the presence of crustal underplating (Grevemeyer et al. 2000). We used results from Ocean Drilling Program (ODP) drill cores and cross-spectral analysis of gravity and bathymetric data to study the impact of the underplating body on the subsidence history and the mode of isostatic compensation along Ninetyeast Ridge. Compared with the adjacent Indian basin, the subsidence of Ninetyeast Ridge is profoundly anomalous. Within the first few millions of years after crustal emplacement the ridge subsided rapidly. Thereafter, however, subsidence slowed down significantly. The most reliable model of isostasy suggests loading of a thin elastic plate on and beneath the seafloor. Isostatic compensation of subsurface loading occurs at a depth of about 25km, which is in reasonably good agreement with seismic constraints. Subsurface loading is inherently associated with buoyant forces acting on the lithosphere. The low subsidence may therefore be the superposition of cooling of the lithosphere and uplift due to buoyant material added at the base of the crust. A model including prolonged crustal growth in the form of subcrustal plutonism may account for all observations.

Description: Available data support a mechanism of buoyancy‐mediated vertical migration by large‐sized diatoms of Rhizosolenia spp. as a means to access “new” nitrogen from deep waters. To assess whether phytoplankton simultaneously satisfy their Fe requirements by this mechanism, field samples collected during summer 1996 at stations located along a transect through the central North Pacific gyre were assayed for the presence of flavodoxin and ferredoxin via Western blot analysis. All samples, regardless of their buoyancy status and the station from which they were collected, had accumulated flavodoxin but not ferredoxin. To understand better the significance of the field results, cultures of Rhizosolenia formosa H. Peragallo were grown in the laboratory with varying levels of total Fe (200 nM–10,000 nM). Fe had little effect on the physiological and photochemical parameters measured for each treatment. Growth rates did not exceed 0.17 d−1 and values of Fv/Fm ranged from 0.48 to 0.62. In addition, R. formosa accumulated only flavodoxin at each level of Fe addition. From these results, it appears that for some rhizosolenids, flavodoxin is constitutively expressed. The underlying basis for the constitutive nature of this flavodoxin is unclear at present, although it is likely that it is ultimately related to chronic Fe deficit incurred in natural waters.

Description: Aquaculture in Germany is a small industry, practiced only in a few specifically suited areas. Marine finfish farming is almost nonexistent but mussel farming is a steady activity with a notable level of production. However, this industry is presently very restricted with no hope for expansion as regulations are stringent and new licences in both fresh and marine waters are extremely difficult to obtain. In addition to State-specific conditions within the Federation, the complexity of the regulatory framework is exemplified by focusing on some key aspects for finfish farming and by specific aspects of mussel farming activities in the Schleswig-Holstein Wadden Sea where environmental protection measures dictate the level of control, mainly as a result of the recent establishment of the National Wadden Sea Park.

Description: Empirical relationships are presented to estimate in fishes, asymptotic length (L∞) from maximum observed length (Lmax), length at first maturity (Lm) from L∞, life span (tmax) from age at first maturity (tm), and length at maximum possible yield per recruit (Lopt) from L∞ and from Lm, respectively. The age at Lopt is found to be a good indicator of generation time in fishes. A spreadsheet containing the various equations can be downloaded from the Internet at http://www.fishbase.org/download as popdynJFB.zip. A simple method is presented for evaluation of length–frequency data in their relationship to L∞, Lm and Lopt. This can be used to evaluate the quality of the length–frequency sample and the status of the population. Three examples demonstrate the usefulness of this method. 2000 The Fisheries Society of the British Isles

Description: A major vector for unintentional species introductions is international shipping. A wide range of organisms have been transported over long distances in ships' ballast tanks and as hull fouling. Although many desk studies and ship sampling programmes have been carried out, little information is available on changing numbers of individuals in ballast water during voyages. Detailed information could assist in evaluating the dimension of species import and future risks of unintentional species introductions by ballast water. The first European study, organised as a concerted action team and financed by the European Union, carried out several long-term and short-term workshops on board ships undertaking international voyages. The preliminary results from sampling the ballast water of the first four oceangoing workshops of this Concerted Action showed a decrease in numbers of specimens and taxa over time.

Description: Water and sediment quality conditions in and around a cage culture unit located in Wismar Bay (Western Baltic Sea, Germany) were investigated during summer 1994 using bacterial group indicators (Enterobacteriaceae, saprophytic bacteria and Vibrio, determined on selective media). Fish were fed once daily with extruded commercial pellets. Over a period of 8 days samples were taken before and after feeding at different sampling points close to or at the cages. The results showed that a drastic (up to 10 times) increase in different bacterial groups occurred inside the cages 10 min after feeding as well as occasionally in the surrounding water. Additional electron-microscopic observations of the bacterial biofilm on the cage nets revealed that a decrease (in comparison with the original number) in total bacteria on the net materials of 9.5 up to 42.8% occurred after feeding. It was concluded that water mixing caused by frenzied swimming just before and during feeding caused a release of bacteria which were growing vigorously on the surfaces of the cage system. Since the pathogenity and hydrophobicity of bacteria are closely related, this process of redistribution of bacteria into the water column could constitute an important stress factor for fish, which could probably also have a negative effect on fish production.

Description: Macroalgal blooms are a growing environmental problem in eutrophic coastal ecosystems world wide. These blooms are dominated typically by only one out of several co‐occurring opportunistic species, which are all favored by increased nutrient loads. We asked whether pronounced dominance of filamentous Pilayella littoralis Kjellm. (Phaeophyceae) over foliose Enteromorpha intestinalis L. (Chlorophyceae) in the Baltic Sea can be explained by interspecific physiological differences. In laboratory experiments, we analyzed uptake kinetics of nitrate, ammonium, and phosphate and the time dependency of uptake rates for both species. We further examined growth rates and nutrient assimilation in relation to single and combined enrichment with nitrate and phosphate, and three different nitrogen sources. Overall, we did not detect distinct differences in uptake, growth, and assimilation rates between P. littoralis and E. intestinalis. Minor differences and the related advantages for single species are discussed. Highest maximal uptake rates were found for ammonium, followed by nitrate and phosphate. Strong time dependency of uptake occurred, with the highest rates during the first 15 to 30 min. Nitrate enrichment had far more of an effect on growth than phosphate. Enrichment with urea, ammonium, and nitrate significantly increased growth rates without interspecific differences. A larger surface area to volume (SA/V) ratio in Pilayella compared with Enteromorpha did not translate into greater physiological capacity. We conclude that species dominance patterns in macroalgal blooms are not always a direct result of different ecophysiological traits among species. Ecological traits such as susceptibility to herbivory are important factors in determining species distribution in the field.

Description: The respiration of coho salmon, Oncorhynchus kisutch, weighing between 20 and 45 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17 °C. The maximum and minimum oxygen concentrations tested were 235 and 41 μmol/L, respectively. Respiration rates were measured for 24 h at 235 μmol/L before the oxygen concentration was lowered stepwise to 157 and 81 μmol/L. In one single trial, the oxygen level was lowered to 66, 53, and 41 μmol/L. Respiration was highly variable in time. Peak activities always occurred during the night. The standard metabolic rate at normoxic conditions was estimated to be around 4 μmol oxygen/g/h. The highest rates reached values close to 15 μmol oxygen/g/h. At reduced oxygen levels the standard oxygen demand slightly increased to 4.5 μmol oxygen/g/h, indicating a higher demand for vital metabolic functions. Due to the decrease of swimming activity, the maximum oxygen uptake rates dropped to 〈 8 μmol oxygen/g/h below 81 μmol/L oxygen concentration. Under long-term conditions, physiological and behavioural adaptations play an important role for survival and need to be considered for the design and operation of fish farm facilities.

Description: Elicitation of Gracilaria conferta (Schousboe ex Montagne) J. ct G. Feldmann with oligoagars resulted in a defense response that was strong enough to kill epiphytic bacteria associated with the alga. Up to 60% of the resident bacterial flora of healthy plants was eliminated within 60 min after addition of neoagarohexaose to the algal medium. Single isolates of agar-degrading bacteria that had been isolated previously from healthy or decaying algal tissues proved to be more sensitive, Some of them were generally unable to survive on healthy G, conferta. Others survived on unelicited plants. Approximately 90% of these more resistant agar degraders were eliminated within 15 min after elicitation. The bacterial degradation of dead tissue of G, conferta resulted in a release of elicitors. The elicitors accumulated in the medium and reached high enough concentrations within 24 h to induce a hypersensitive response in healthy algae, The eliciting agent could be destroyed with beta -agarase and was thus probably oligoagar, Application of antibiotics prevented the accumulation of the elicitor, which indicated that bacteria were responsible for its release from the algal biomass, The hypersensitive response of G. conferta after contact with oligoagars is thus a true defense response, because it enables the plant to protect itself efficiently from enzymatic attacks on its cell wall.

Description: The sepiolid squid Euprymna scolopes forms a bioluminescent mutualism with the luminous bacterium Vibrio fischeri, harboring V. fischeri cells in a complex ventral light organ and using the bacterial light in predator avoidance. To characterize the contribution of V. fischeri to the growth and development of E. scolopes and to define the long-term effects of bacterial colonization on light organ morphogenesis, we developed a mariculture system for the culture of E. scolopes from hatching to adulthood, employing artificial seawater, lighting that mimicked that of the natural environment, and provision of prey sized to match the developmental stage of E. scolopes. Animals colonized by V. fischeri and animals cultured in the absence of V. fischeri (aposymbiotic) grew and survived equally well, developed similarly, and reached sexual maturity at a similar age. Development of the light organ accessory tissues (lens, reflectors, and ink sac) was similar in colonized and aposymbiotic animals with no obvious morphometric or histological differences. Colonization by V. fischeri influenced regression of the ciliated epithelial appendages (CEAs), the long-term growth of the light organ epithelial tubules, and the appearance of the cells composing the ciliated ducts, which exhibit characteristics of secretory tissue. In certain cases, aposymbiotic animals retained the CEAs in a partially regressed state and remained competent to initiate symbiosis with V. fischeri into adulthood. In other cases, the CEAs regressed fully in aposymbiotic animals, and these animals were not colonizable. The results demonstrate that V. fischeri is not required for normal growth and development of the animal or for development of the accessory light organ tissues and that morphogenesis of only those tissues coming in contact with the bacteria (CEAs, ciliated ducts, and light organ epithelium) is altered by bacterial colonization of the light organ. Therefore, V. fischeri apparently makes no major metabolic contribution to E. scolopes beyond light production, and post-embryonic development of the light organ is essentially symbiont independent.

Description: Morphology of statoliths and anatomy of statocysts were studied in five species of Gonatidae, Moroteuthis robusta (Onychoteuthidae) and Galiteuthis phyllura (Cranchiidae) from the northern Bering Sea, and Todarodes pacificus (Ommastrephidae) from the Pacific waters near Japan. A special experiment was carried out in order to observe statolith mobility on the macula statica and possible endolymph flows within the statocyst in freshly caught gonatid squid Berryteuthis magister. It was found that the statolith may deviate at small acute angles around three axes running through its centre of rotation (located near the spur) without any visual damage of its attachment area to the macula. This finding enabled us to re-consider previous theories and to create a new model of the squid statocyst functioning with the statolith as detector of multidimensional movement. Two types of statolith morphology are distinguished: demersal type statoliths characteristic of near-bottom decapods, and pelagic type statoliths characteristic of all pelagic squids and not dependent on their systematic position. Phylogenetic and ecological features of the statocyst and statolith structure are established. Possible evolutionary trends in development of different types of statocysts in decapods are discussed.

Description: A type of apparent photoreceptor, the nuchal organ, is described in the sepiolid squid Euprymna scolopes. These vesicles are identified in a variety of other cephalopod species. The nuchal organs have specific structural similarities to the already well-described photosensitive vesicles. Both organs have a distinct vesiculate structure and possess a rind consisting of several types of cells. Certain rind cells from both organs send processes with microvilli into the lumen of the vesicle forming a core area. Within the cores of both organs numerous microvilli occupy much of the core volume. These histological similarities provide strong evidence that the nuchal organs, like the photosensitive vesicles, are photoreceptors. Three distinct differences also exist between the nuchal organs and photosensitive vesicles: (1) the location of the nuchal organs differs from that of all known photosensitive vesicles in cephalopods; (2) the location of the nuchal organs is highly conservative in decapod cephalopods compared to the varying locations of the photosensitive vesicles; (3) the degree of structural order generally found within photosensitive vesicles is not apparent in the nuchal organs. The function of the nuchal organ is probably different from previously described photoreceptors in cephalopods.

Description: he gut contents of a female specimen of Graneledone cf. boreopacifica collected from the caldera wall of Axial Volcano, near an active hydrothermal vent in the Northeast Pacific Ocean are reported. At least 30 individual gastropods and 46 individual polychaetes are represented in the gut contents by hard parts. Shell fragments and shells removed from the gut allow ready identification of the gastropods Provanna variabilis and Lepetodrilus fucensis, both of which are known only from North Pacific hydrothermal vents. Jaws of polychaete worms are identified as those of the nereidid, Nereis piscesae, and the predatory polynoids, Levensteiniella kincaidi and an unidentified species in the subfamily Branchinotogluminae. Not only was a considerable volume of prey hard parts ingested, the gastropod shells had been crushed before being ingested. The large size of the beaks in this genus of octopus and the increased area they offer for insertion of the superior mandible muscle, the prime mover in beak closure, support the hypothesis that these beaks exert sufficient force to crush the gastropod shells. Although cephalopods had been reported to be absent from hydrothermal vents, the data presented here demonstrate that not only do they occur in vent habitats, they actively prey on vent fauna.

Description: Ballast water of ships has been recognized as a major vector for the unintentional transfer of exotic aquatic organisms between and within many parts of the world. Studies in several European ports have shown that most of the ballast water discharged originates from nearby sea areas indicating the importance of secondary introductions. However, the patterns of interregional transfer of exotic species within Europe remain largely unknown. The present study examined the transfer of phyto- and zooplankton organisms in the ballast water to assess the potential for the transport of invasive aquatic species between the Baltic Sea and the open Atlantic coast of Europe. Six potentially toxic phytoplankton species were found in the ballast water examined. In four ballast water sampling trials no significant changes in abundance of both phyto- and zooplankton organisms were observed during first 3–4 days of experiment. Even in the end of the longest sampling trial (15 days) millions of plankton organisms were found. The results obtained indicate the importance of interregional European shipping in the dispersal of exotic plankton organisms.