Changes in the fish fauna associated with a sub-Antarctic <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> kelp forest in response to canopy removal

The fish fauna associated with a Macrocystis pyrifera forest and the effects of the canopy removal on this fauna were studied in the Beagle Channel, Tierra del Fuego. Seasonal changes and differences in the fish communities that inhabit the canopy and the holdfast were also studied. Two patches of kelp forest separated by 200 m were selected. In one, the canopy was removed periodically while the other was used as a control. Samples were collected seasonally, from autumn 1999 to 2001. Fish fauna in the water column was sampled using trammel nets and holdfast fish fauna was sampled by removing the complete holdfast. Different assemblages of fish species were captured in the water column (surface and bottom) and in the holdfast. In the former there were mainly pelagic and benthopelagic species and the latter predominantly demersal species. The principal effect of the canopy removal was a drop in the abundance (and total weight) of Paranotothenia magellanica (doradito), the species with the strongest relationship with the canopy, principally at the surface of the treated patch probably due to a reduction in the availability of refuges. A high degree of seasonality was observed for fish species’ total weight, abundance and diversity, with higher values in summer and autumn. Taking into account our data and available data on kelp growth in the same locality, we suggest of cutting the kelp forest (preferably those farther away from the coast) once a year in winter or early spring, in order to minimize impact on the fish community.     

The unique nature of the formation of parasitic fish fauna in the reservoirs of the Daugava River

The formation of parasite fauna of fishes from water reservoirs of the Daugava differs from that of plain type water reservoirs of the moderate zone. Instead of expected flourishing of limnophilic elements an intense, increasing with years impoverishment of the specific composition of nearly all systematic groups of fish parasites is observed in the studied reservoirs. The impoverishment of the parasite fauna in the water reservoirs is associated first of all with their relatively small sizes, frequent and strong fluctuations of the water level and repeated dryings of large bottom areas. The investigations show that such a picture of fish parasite fauna genesis is observed in all relatively small water reservoirs with frequent and strong fluctuations of water level.     

Fossil fish otoliths from the Chibanian Miyata Formation,Kanagawa Prefecture,Japan, with comments on the paleoenvironment

The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in the Middle-Late Pleistocene is known for its rich marine fauna that accommodated both the warm and cold water taxa brought by the Kuroshio and Oyashio Currents, respectively. However, little is known on the paleoichthyofauna in this area and the processes shaping the marine ichthyofauna of modern southern Kanto. We used fossil fish otoliths and teeth discovered in the Sha’ana Tuffaceous Sand Member belonging to the Chibanian Miyata Formation, exposed at Sha’ana-dai, Miura City, Kanagawa Prefecture, Japan, to reconstruct the paleoichthyofauna and its associated paleoenvironment and explore the content of fish assemblages during this period. The Sha’ana Tuffaceous Sand Member was composed of upper sandy mud and lower muddy sand horizons at the exposure. A total of 1,675 fish remains were collected from this site, of which 1,389 were assigned to 62 distinct taxa (20 orders, 31 families). The taxonomic composition revealed taxa from various environments, including shallow continental shelf, epi- to meso-pelagic settings, and the majority were from a generally temperate climatic zone. Paleoenvironmental analyses suggested that the fish assemblages were from the continental shelf (approximate depth of 100–200 m) in a temperate sea where both warm Kuroshio and cold Oyashio Currents had an influence on the biota. The analysis also showed that two boreal fishes, namely Clupea pallasii and Theragra chalcogramma, once had a wider distribution that extended to the southwestern areas of the Paleo-Tokyo Bay. This study provides a more complete view of the related paleobiogeography of marine fishes during the Chibanian and is essential for reconstructing the evolutionary processes of the rich ichthyofauna in the southern Kanto.     

Changes in gastropod assemblages in freshwater habitats in the vicinity of Basel (Switzerland) over 87 years

Net pen fish farms generally enrich the surrounding waters and the underlying sediments with nutrients and organic matter, and these loadings can cause a variety of environmental problems, such as algal blooms and sediment anoxia. In this study we test the potential of biofiltration by artificial reefs for reducing the negative environmental impacts surrounding fish farms in the Gulf of Aqaba, Red Sea. Two triangular-shaped artificial reefs (reef volume 8.2 m³) constructed from porous durable polyethylene were deployed at 20 m; one below a commercial fish farm and the other 500 m west of this farm in order to monitor the colonization of these reefs by the local fauna and to determine whether the reef community can remove fish farm effluents from the water. Both reefs became rapidly colonized by a wide variety of organisms with potential for the removal of compounds released from the farms. Within the first year of this study fish abundances and the number of species reached 518–1185 individuals per reef and 25–42 species per reef. Moreover, numerous benthic algae; small sessile invertebrates (bryozoa, tunicates, bivalves, polychaetes, sponges, anemones) and large motile macrofauna (crustaceans, sea urchins, gastropods) settled on the reef surfaces. Depletion of chlorophyll a was measured in the water traversing the artificial reefs in order to assess the biofiltration capacity of the associated fauna. Chlorophyll a was significantly reduced to a level 15–35% lower than ambient concentrations. This reduction was greatest at intermediate current speeds (3–10 cm s^–1), but was not influenced by current direction. The reef structures served as a successful base for colonization by natural fauna and flora, thereby boosting the local benthic biodiversity, and also served as effective biofilters of phytoplankton.     

Flexible Spatial Orientation and Navigational Strategies in Chambered Nautilus

Nautilus is a remnant of an externally shelled cephalopod lineage that flourished between 450 and 60 million years ago. It is a deep‐water scavenger that lacks the complex brain and behavioural repertoire of its soft‐bodied relatives, the coleoid cephalopods. Nautilus makes repeated, nightly migrations from deep to shallow water along coral reef slopes to forage, thus an ability to navigate to known locations may be selectively advantageous. Alternatively, drifting passively with the current may be sufficient to locate food and mates distributed randomly over a large area. The derived neural structures that support learning and memory in coleoids are absent from the nautilus brain, indicating that substantial differences between learning abilities in nautilus and coleoids are likely. However, our previous work has demonstrated both associative and spatial learning in nautilus. In laboratory experiments, we tested whether Nautilus pompilius could learn to navigate towards a goal location using either visual cues or motor responses. Results indicate that animals relied both on proximate and distant visual cues to orient but did not use egocentric cues, a somewhat surprising finding given that nautilus spends most of its time in near darkness. Animals learned visual information rapidly and in some cases were able to switch to other tactics when salient visual cues were removed or manipulated.     

Food-habitat relationship of harbour seals and black cormorants in Skagerrak and Kattegat

Comparative studies on the food of the black cormorant Phalacrocorax carbo and the harbour seal Phoca vitulina were carried out in two contrasting habitat types. Both species feed predominantly on bottom-dwelling fish. Black cormorants are able to utilize fish found both on vegetation-covered and naked sea beds at a water depth of less than 10 m, while harbour seals feed mainly on soft sea bottoms above 30 m where vegetation is scarce or lacking. The food overlap of the two piscivores is large in environments where large shallow sea bottoms are available, and small in areas where sea bottoms of soft material is found at greater depth. In areas where the shallow bottoms are covered by vegetation only, cormorants are able to feed on the fish species inhabiting this kind of environment. There is no evidence that these predators make a choice regarding prey species.     

Geochemistry and palaeogeography of upper Ordovician glaciogenic sedimentary rocks in the Table Mountain Group, South Africa

Evidence for a late Ordovician glaciation is best known from northern Africa and locally in South Africa, and western South America. The South African glacial deposits (Pakhuis Formation of the Table Mountain Group) are present in the western part of the Cape Fold Belt. Two thin diamictites are succeeded by a coarsening upward shale-siltstone unit known as the Cedarberg Formation. These glaciogenic rocks are associated with one of the world's greatest accumulations of mature sandstones. The diamictites are under- and overlain by shales and sandstones that have undergone extensive alteration, presumably as a result of chemical weathering. Some diamictite samples have low values for a Chemical Index of Alteration (CIA), in keeping with their inferred glacial origin. Immediately above the glaciogenic diamictites, black shales, comprising the basal Soom Member of the Cedarberg Formation preserve an unusual soft bodied fauna and are enriched in Mo, U and other trace elements. The unusual chemical composition of these shales is attributed to starved basin conditions and a reducing environment during a rapid sea level rise that accompanied demise of the late Ordovician glaciers. The late Ordovician glacial deposits of western South Africa are widely regarded as the distal deposits of a large continental ice sheet centred on North Africa but they may have been partly derived from piedmont glaciers that descended from highlands formed as a result of late Ordovician orogeny.     

Community structure of fishes attracted to shallow water fish aggregation devices off South Carolina,U.S.A.

Synopsis Twenty-two fish aggregation devices were deployed in 14 m of water off South Carolina. Species composition and abundance were determined by diver visual census on eight occasions from May through November, 1985. A total of 21 families and 36 species of fishes was observed at 121 stations. Pelagic fishes dominated the fauna with a 99.3% relative abundance, and Decapterus punctatus accounted for 97.6% of the individuals. Caranx crysos, Diplectrum formosum, Decapterus punctatus, Centropristis striata and Monacanthus hispidus were the most frequent species. Total fish abundance, number of species and abundance of four of the six most common species were significantly affected by season. Hurricane activity may have caused a significant drop in pelagic fish abundance at the FADs in July. No significant correlations among species abundances were found after removal of season and FAD type effects. Spatial zonation and seasonal occurrence patterns suggest some competition among pelagic fishes. Several factors that regulate FAD faunal abundance and composition are hypothesized, including: juvenile fish availability, availability of shelter, availability of adequate food resources, interspecific and intraspecific competition, severe sea conditions, and sporadic intrusions of large predatory fishes. It is hypothesized that the abundances of benthic and pelagic FAD fishes are correlated and that there is a direct or indirect energetic link between shallow water pelagic and benthic fish assemblages near FADs.     

Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale Lagersta¨tte, South Africa

ABSTRACT. Orthoconic cephalopods from the Soom Shale Member (Ashgill) are exceptionally preserved and are colonized by lingulate brachiopods and cornulitids. Other fossils commonly associated with orthocones include myodocopid ostracodes and chitinozoans. Size distribution analysis of the brachiopods on one orthocone indicates that it was colonized in vivo. Four orthocone radulae are preserved extending the record of these structures 50 My back to the late Ordovician. Orthocone radula configuration is more similar to that of ammonoids and coleoids than to that of nautiloids.     

Hard rock versus soft bottom: the fauna associated with intertidal mussel beds on hard bottoms along the coast of Chile,and considerations on the functional role of mussel beds

The fauna associated with hard bottom mussel beds along the exposed Pacific coast of Chile was examined. The abundance of adult (>10 mm body length) purple mussels Perumytilus purpuratus varied between 32 and 75 individuals per 50 cm², and their biomass between 4.8 and 8.6 g AFDW per 50 cm² at eight sampling sites between Arica (18°S) and Chiloé (42°S). At all sampling sites, the associated fauna was dominated by suspension-feeding organisms (cirripeds, spionid and sabellid polychaetes, a small bivalve) followed by grazing peracarids and gastropods. Predators and scavengers also reached high abundances while deposit- and detritus-feeding organisms were of minor importance. The majority of organisms associated with these hard bottom mussel beds feed on resources obtained from the water column or growing on the mussels rather than on materials deposited by the mussels. This is in contrast to the fauna associated with mussel beds on soft bottoms, which comprises many species feeding on material accumulated by mussels (faeces and pseudofaeces) and deposited within the mussel bed. Many of the organisms dwelling between mussels both on hard bottoms and on soft bottoms have direct development, but organisms with pelagic development also occur abundantly within mussel beds. We propose that species with direct development are disproportionately favoured by the structurally complex habitat with diverse interstitial spaces between the mussels, which provides ample shelter for small organisms. We conclude that mussels on hard-bottoms primarily provide substratum for associated fauna while mussels on soft bottoms provide both substratum and food resources. Electronic Publication     

The Sirius Passet Lagerstätte of North Greenland—A geochemical window on early Cambrian low‐oxygen environments and ecosystems

The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional water‐column chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (Fe_HR/Fe_T), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ¹⁵N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2–0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with sea‐level change, and where this early Cambrian biota was established in conditions with very low oxygen.     

INTRODUCTION

.In view of the growing importance of fish for native consumption, the resources of the African lakes are sure to be exploited in the near future, but it is essential to have a sound understanding of the fish and other fauna and flora in each lake before exploitation is started. This paper places on record the available data for Lake Rudolf and Lake Baringo, on which no previous ecological work had been attempted.
Lake Rudolf is characterized by a high temperature and very alkaline water, and contains a variety of environments inhabited by different fish-associations. The fauna has pronounced nilotic affinities, except that there is only one member of the family Mormyridae. Several species, however, have come to differ from their nilotic ancestors, and the comparison of the fauna with that of other waters can be used as evidence for past changes in the drainage systems of East Africa.
The fish fauna of Lake Rudolf is roughly divisible into three main associations of species–one in the inshore waters, one in the open water, and one near the bottom. Prom data supplied by large numbers of stomach examinations, the food-chains for each of these habitats can be reconstructed.
Lake Baringo is less warm, the water has a relatively low alkalinity, and is uniformly shallow and muddy. The fish fauna consists of few species, and shows affinities with that of the East African rivers which flow to the Indian Ocean.
Owing to the shallowness of Lake Baringo, there is no differentiation into species-associations, and the food-chains are complicated by the presence of food from the bottom in all the species of fish.
The bulk of this paper contains analyses of field-observations on the size, feeding and breeding habits of each of the species found in the lakes,     

The cranial anatomy and taxonomy of Peloneustes philarchus (Sauropterygia,Pliosauridae) from the Peterborough Member (Callovian,Middle Jurassic) of the United Kingdom

Abstract: Peloneustes philarchus is the most abundant pliosaurid from the Peterborough Member of the Oxford Clay Formation (Callovian) of the UK. It is a valid taxon possessing a unique character combination, including a single autapomorphy: the interdentary symphysis is raised dorsally on a narrow platform. Twenty‐one specimens can be positively referred to P. philarchus. However, other specimens previously referred to Peloneustes, from the Peterborough Member near Peterborough, and the lower Oxfordian strata of Marquise, northern France, represent distinct, unnamed taxa. The skull of P. philarchus is described in detail, including new information from an uncrushed, three‐dimensionally preserved specimen and a specimen with a well‐preserved palate. Well‐preserved material clearly indicates that P. philarchus lacked nasals, but possessed a lacrimal. A previously unrecognised ‘palpebral’ forms part of the dorsal orbit margin adjacent to the prefrontal. The number of maxillary (30–31) and dentary (36–44) alveoli, the number of dentary alveoli adjacent to the mandibular symphysis (13–15), the number of foramina on the frontal and jugal, the breadth of the parasphenoid, breadth of the anterior (narial) process of the palatine and the presence of a lappet of the angular that extends onto the posterodorsal surface of the retroarticular process vary among individuals but are not considered sufficient to justify the recognition of new taxa. The presence of an open palpebral–prefrontal suture, the size of the ventral midline tubercle of the basioccipital and the presence of an anterior interpterygoid vacuity seem to vary with body size.     

Trophic structure of cold-water coral communities revealed from the analysis of tissue isotopes and fatty acid composition

The trophic structure of cold-water coral reef communities at two contrasting locations, the 800-m deep Belgica Mounds (Irish margin) and the 300-m deep Træna reefs (Norwegian Shelf), was investigated using stable isotope (δ¹³C and δ¹⁵N) and fatty-acid composition analysis. A broad range of specimens, with emphasis on (commercial) fish specie's, and organic matter sources were sampled using a variety of tools. Irrespective of the environmental and geographical setting, the δ¹⁵N values indicated that the food web encompasses roughly 1.5 to 3 trophic levels. Mobile echinoderms, i.e. sea urchins and sea stars, had highest δ¹⁵N values, indicative of a high trophic position in the food web. The fraction of bacterial fatty acids in reef fauna was generally low (<5%), indicating that enhanced bacterial production in the water column through seafloor seepage of nutrients (‘hydraulic theory’) does not form a significant energy pathway into the food web. The high fraction of algal and essential fatty acids in reef fauna and fish at both locations indicates a close coupling with surface productivity, but the transport mechanism depends on the hydrographic setting. At Træna, Calanus copepods and euphausiids form an additional link between primary production and fish, which is largely absent at Belgica Mounds. At Belgica Mounds, the reef community is primarily supported by phytodetritus, as evidenced by the high contribution of algal fatty acids in faunal tissue and seasonal chlorophyll a deposition and marine snow at the reef. The environmental setting of cold-water coral reefs influences the structure of the associated food web.     

Impact of acidification and eutrophication on the distribution of fish species in shallow and lentic soft waters of The Netherlands: an historical perspective

The species richness and composition of fish assemblages were examined in lentic soft waters in The Netherlands. The selected bodies of water reflected a large variation in geomorphological and limnological factors. In total, 24 fish species were encountered in Dutch soft waters. During 1983–1984 Esox lucius, Perca fluviatilis, Rutilus rutilus, Scardinius erythrophthalmus, Tinca tinca and Umbra pygmaea were quite common. In slightly acid and alkaline waters (pH≥5) Rutilus rutilus, Scardinius erythrophthalmus, Perca fluviatilis, Ictalurus nebulosus and Cyprinus carpio accounted for about 90% of the total number of specimens in the catches. Strongly acid waters (pH < 5) generally were fishless. If fish were present in these waters, however, the catches mainly consisted of Umbra pygmaea. Only in a few strongly acid systems were other species collected. The lowest pH at which certain fish species occurred varied from 3.1 to 7.0. In particular, Umbra pygmaea was extremely acid-tolerant. The percentage of waters which harboured fish as well as the average number offish species per water decreased steeply between pH 6 and 4. The sampled waters showed remarkable differences in their fish assemblages. With hierarchical classification, six groups of waters could be distinquished with respect to their fish fauna. The site groups are defined and characterized physico-chemically and their fish assemblages described. Multivariate analysis showed that the structure of fish communities is strongly related to the pH, the alkalinity, trophic level and the ionic composition of the water. Comparison of historical and recent data on the occurrence of fish strongly indicated that in many sampling sites fish species or even entire fish assemblages had disappeared. Ordination of available data also illustrated recent changes in community structure. At least 67% of the nowadays extremely acid waters formerly harboured fish populations. The impoverishment of fish communities or the total loss of fish were primarily caused by cultural acidification. Limited nutrient enrichment of soft waters only resulted in minor alterations of fish assemblages.     

Expression of interferon type I and II, Mx and gammaIP genes in the kidney of Atlantic salmon, Salmo salar, is induced during smolting

The expression in kidney tissue of interferon type I (IFNalpha) and type II (IFNgamma) genes and two of their inducible genes, Mx and gammaIP were monitored, using qRT-PCR, in a population of Atlantic salmon prior to and over the period of smolting and sea water transfer. The smolting process was induced by photoperiod manipulation in October and smolts were transferred to sea water in December. Prior to extending the light period in October, the fish showed extremely low level expression of the genes assayed. However, immediately on extending the light and up until 1 week after transfer to sea water, 26 of the 90 fish sampled showed up-regulated expression for IFNalpha, Mx and gammaIP. The highest levels were shown by two fish on the 2 days prior to sea water transfer. Eleven fish displayed elevated expression of IFNgamma but there was no apparent association with smolting or sea water transfer or expression of the other genes. At the end of the sampling period, 30 fish were tested by standard virological methods and found to be virus free. The results indicate that during the smolting process, Atlantic salmon consititutively express IFNalpha and Mx mRNA. Those individuals which express Mx close to the time of transfer to sea water would be expected to have high levels of the anti-viral Mx protein in tissues for the longest time after sea water transfer. This could provide an innate defence against viral pathogens which post-smolts may encounter for the first time on entering the marine environment. Those individuals which express Mx early in the smolting process may be more at risk of developing IPN or other viral diseases as post-smolts.     

The palaeobiology of belemnites – foundation for the interpretation of rostrum geochemistry

Belemnites are an extinct group of Mesozoic coleoid cephalopods with a fossil record ranging from the early Late Triassic [about 240 million years ago (Mya)] to the Cretaceous/Palaeogene boundary (65 Mya). Belemnites were widely distributed, highly abundant and diverse, and an important component of Mesozoic marine food webs. Their internal shells, specifically their low‐Mg calcite rostra, have been used as palaeoenvironmental carbonate archives for the last 70 years. This is primarily due to the assumption that the rostrum calcite formed in equilibrium with the oxygen isotope composition of ambient sea water. Of prime importance for the reliable interpretation of isotope data derived from these biogenic carbonates is a robust reconstruction of the palaeobiology of their producers. Here we provide a critical assessment of published reconstructions of belemnite soft‐body organization and their lifestyle and habitats. Different lines of evidence, including sedimentological, geochemical, morphological, and biomechanical data, point towards an outer shelf habitat of belemnites, for some taxa also including the littoral area. Belemnite habitat temperatures, oxygen content, salinities, and life span are constrained based on observations of the ecology and life history of modern coleoids. Belemnite habitat depth might have been largely controlled by food and temperature, with a temperature optimum between 10°C and 30°C. The distribution of modern coleoids is for most species restricted to well‐oxygenated water masses and a salinity between 27 and 37 psu. The trophic position of belemnites as both predators and prey is documented by unique fossil finds of stomach contents and soft tissue preservation, such as jaws, hooks, and ink sacs. Belemnites were medium‐sized predators in the epipelagic zone (not deeper than ～200 m) hunting for crustaceans, other cephalopods, and fishes. Taxa with elongated rostra probably were fast and highly manoeuvrable swimmers. Forms with conical rostra represent slow but highly manoeuvrable swimmers, and forms with depressed rostra likely had a bottom‐related life habit. Predators of adult belemnites were sharks, bony fishes, and marine reptiles. Belemnites, like most of the modern coleoids, were relatively short lived, most likely living only for 1–2 years. Understanding the biomineralization of belemnite rostra is highly relevant for an improved interpretation of their geochemistry. Here we confirm that belemnite rostra are composed of low Mg‐calcite fibres, but they do not contain distinct types of laminae. These fibres are composed of two distinct calcite phases. One phase is a filigree network of tetrahedral organic‐rich calcite and the second phase is represented by organic‐poor calcite.     

Seven Decades of Change in the Zooplankton (s.l.) of the Nile Delta Lakes (Egypt), with Particular Reference to Lake Borullus

Around the 1930s, the zooplankton (and benthos) of the Nile delta lakes, and Lake Borullus in particular, had a mixed, eutrophic facies, with marine and mesohaline elements dominant for about eight months per year, and freshwater species taking over during the four months of the Nile flood. After the Aswan dam became operational, this regime changed: a steady supply of agricultural drainage water of Nilotic origin consistently freshened the delta. Thus, except in the immediate vicinity of their outlet to the sea, the lakes became almost fresh. Only during the rare and short‐lived (one‐three weeks) occasions when Aswan closes in winter, marine water is sucked in, and along with it, a saline fauna temporarily becomes re‐established in the east and centre of lake Borullus, and presumably of the other delta lakes as well. This marine fauna remained the same over 70+ years of observations. The freshwater component, in contrast, partly nilotic, partly mediterranean, changed deeply over time. First, the fraction of species from temporary waters disappeared, as well as (among copepods and cladocerans) all large‐bodied species. Several cladocerans and copepods with a euro‐mediterranean range appeared and diluted the pre‐existing Afrotropical fauna. The abundance of small cladocerans and, especially, rotifers increased by a factor ten or more. This latter change is believed to reflect two pressures. In a first phase, a re‐arrangement of the lake's fish fauna (a top down force) occurred. Freshwater fish replaced marine diadromic species, and their predation pressure on the zooplankton preferentially removed large‐bodied prey. In a second phase, increased agricultural drainage caused eutrophication (a bottom‐up force) and larger filtrators (cladocerans, some copepods) began to be replaced by small filtrators (rotifers). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Starvation survival of the fish pathogenic bacteria Vibrio anguillarum and Vibrio salmonicida in marine environments

Abstract The possible fate in sea water of the two fish pathogenic bacteria Vibrio anguillarum and Vibrio salmonicida is discussed on the basis of microcosm experiments with these and other copiotrophic bacteria. Recent articles dealing with the survival of fish pathogens are reviewed, and the reported survival capacities are discussed in relation to ecological mechanisms, such as death, and predation, leading to the removal of bacteria from the water column.     

Interaction of mineral elements in sea water and shell of oysters (Crassostrea virginica (Gmelin)) cultured in controlled and natural systems

The interaction is reported of selected chemical elements (cadmium, calcium, copper, iron, magnesium, manganese, strontium, and zinc) in cultured sea water, with soft tissues, prismatic calcite of the right valve, and foliated calcite of right and left valves of genetically similar American oysters, Crassostrea virginica (Gmelin) grown in a natural habitat and in two environmentally controlled experimental systems (flow-through and recycle). The addition of trace elements as algal nutrients in ambient sea water was reflected in higher concentrations of trace metals in shells and soft tissues of oysters grown in experimental systems. Calcium was relatively uniformly distributed in major regions of valves from the three habitats, even though its concentration fluctuated widely in sea water in experimental systems. Magnesium and strontium were most concentrated in valves of oysters grown in the recycle system (magnesium in the prismatic layer of the shell and strontium in the foliated calcite). Iron was uniformly distributed. Cadmium, copper, manganese, and zinc were most concentrated in the prismatic calcite of valves from the flow-through system. In soft tissues, calcium was more concentrated in oysters from experimental systems than in those from the natural habitat. Manganese was about equally distributed in soft tissues from the three habitats, whereas copper and iron were more concentrated in soft tissues in experimental systems than in the natural habitat, and were many times more concentrated in soft tissues than in valves from all three habitats. As concentrations of magnesium, strontium, mangenese, zinc, and cadmium increased in valves in experimental systems, pigmentation of valves decreased. The study confirmed the capacity of oysters to concentrate several elements in their valves as concentration of these elements increased in ambient sea water and disclosed the heterogeneous distribution of these elements in major regions of the valves.