Genetic heterogeneity among <Emphasis Type="Italic">Eurytemora affinis</Emphasis> populations in Western Europe

Evolutionary diversification of the broadly distributed copepod sibling species complex Eurytemora affinis has been documented in the northern hemisphere. However, the fine scale geographic distribution, levels of genetic subdivision, evolutionary, and demographic histories of European populations have been less explored. To gain information on genetic subdivision and to evaluate heterogeneity among European populations, we analyzed samples from 8 locations from 58° to 45°N and 0° to 23°E, using 549 base pairs of the mitochondrial cytochrome oxidase subunit I (COI) gene. We discovered three distinct lineages of E. affinis in Western Europe, namely the East Atlantic lineage, the North Sea/English Channel (NSEC) lineage, and the Baltic lineage. These geographically separated lineages showed sequences divergence of 1.7–2.1%, dating back 1.9 million years (CI: 0.9–3.0 My) with no indication of isolation by distance. Genetic divergence in Europe was much lower than among North American lineages. Interestingly, genetic structure varied distinctively among the three lineages: the East Atlantic lineage was divided between the Gironde and the Loire populations, the NSEC lineage comprised one single population unit spanning the Seine, Scheldt and Elbe rivers and the third lineage was restricted to the Baltic Proper (Sweden). We revealed high haplotype diversity in the East Atlantic and the Baltic lineages, whereas in the NSEC lineage haplotype diversity was comparatively low. All three lineages showed signs of at least one demographic expansion event during Pleistocene glaciations that marked their genetic structure. These results provide a preliminary overview of the genetic structure of E. affinis in Europe.     

Reproductive cycles in two populations of the Pacific sand dollar Dendraster excentricus

East Pacific swimming crabs are poorly known ecologically. We trawled samples along 4 estuarine-continental shelf transects to provide information on the population structure and species composition of portunids along environmental stress gradients. Portunids comprised almost 99% of the benthic crabs. Callinectes toxotes dominates the freshest estuarine areas, but is replaced by C. arcuatus in estuary mouth and shallow-shelf samples. Deeper shelf samples are dominated by Euphylax robustus and Portunus sper. Great numbers of E. dovii, a pelagic species, were taken on the shelf; their size distribution implies intraspecific competition. Evidence is given that differences in salinity tolerance account for differential landward limits, but competition, predation by fishes, increased fouling and decreased available food exclude eurytopic species from physicochemically equable shelf waters.     

Genetic evidence for the existence of cryptic species in an endangered clam <Emphasis Type="Italic">Coelomactra antiquata</Emphasis>

Coelomactra antiquata is a commercially important bivalve species, but has been suffering from severe population decline due to over-exploitation and the deterioration of environmental conditions. Previous genetic survey of C. antiquata conducted with allozymes combined with morphology revealed high levels of genetic differentiation between northern and southern populations which suggests a cryptic species might exist in C. antiquata. To test this hypothesis, amplified fragment length polymorphisms (AFLPs) and 16S rRNA gene sequence were used to re-evaluate the spatial genetic structure of six populations of C. antiquata along the coast of China. Both genetic markers display a sharp genetic break between the four northern populations (northern lineage) and two southern population (southern lineage). Large numbers of private alleles (AFLP) were found within the northern or southern populations and a deep divergence of about 6.5% in 16S rRNA gene sequence between the northern and southern lineages suggests the occurrence of potential cryptic or sibling species of C. antiquata. Applying previously published rates of mutation, divergence between the two lineages is estimated to have occurred approximately 3 million years ago and may be due to allopatric isolation during the middle Pliocene times. While no genetic differentiation was found within the northern or southern populations in both AFLP and 16S mtDNA markers, the results indicate that the northern and southern lineage should be managed separately and any translocation between the two areas should be avoided.     

Cryptic speciation in the recently discovered American cycliophoran <Emphasis Type="Italic">Symbion americanus</Emphasis>; genetic structure and population expansion

Symbion americanus was recently described as the second species in the phylum Cycliophora, living commensally on the American commercial lobster Homarus americanus. A previous genetic analysis of American and European populations of cycliophorans suggested that haplotype divergence in S. americanus was much greater than in its European counterpart S. pandora. This study examined the population structure and demographics of 169 individuals thought to belong to S. americanus collected from lobsters over 13 North American localities (Nova Scotia, Canada to Maryland, USA) between October 2003 and January 2006. Cytochrome c oxidase subunit I sequence data clearly suggested the presence of three cryptic lineages in a species complex, often co-occurring in the same lobster specimens. One of these lineages, named the “G” lineage, was represented by very few individuals and therefore was excluded from subsequent statistical analyses. The other two sympatric lineages, named the “T” and “C” lineages, showed different population structure and demography. Although limited geographic structure was found in the T lineage, the C lineage showed higher nucleotide and haplotype diversity values, as well as more variation between localities. The data also indicated that the T lineage underwent a recent population expansion, suggesting that the C and T lineages may have speciated in allopatry but a subsequent population expansion may have been responsible for their current sympatric distribution. Studies on the anatomy and ecology of the sympatric lineages of this species complex should provide further information on the identity of the holotype of S. americanus, which currently cannot be ascribed to any of the three cryptic lineages.     

Deposit-feeding amphipods (Monoporeia affinis) reduce the recruitment of copepod nauplii from benthic resting eggs in the northern Baltic Sea

We experimentally investigated the effect of different densities of the burrowing, deposit-feeding amphipod Monoporeia affinis on the recruitment of zooplankton from benthic resting eggs. Intact sediment cores with in situ density and species composition of zooplankton resting eggs and benthic fauna were collected in the northern Bothnian Sea, part of the Baltic Sea. We removed as many M. affinis as possible from the cores and then added different numbers of M. affinis to the cores to generate a range of densities. The cores were exposed to different densities of M. affinis for either 3 or 40 days, after which the hatched zooplankton was registered. One subset of the cores were initially incubated under low temperature (2–3 °C, to prevent hatching) for 37 days (the resting phase), to allow for effects of M. affinis on unhatched resting eggs. These cores were then incubated under higher temperature (13 °C) for 3 days (the hatching phase), to induce hatching and allow for effects on hatching or hatched specimens. In a second subset of cores with the same time and temperature schedule, the M. affinis density was experimentally reduced at the start of the hatching phase, to evaluate the effect of M. affinis during the hatching phase. To a third subset of cores, we immediately initiated the hatching phase, without an experimental resting phase, to evaluate the effects induced during the resting phase. The most common zooplankton species that hatched was Eurytemora affinis (Copepoda), followed by Bosmina longispina maritima (Cladocera). In all cores that were subjected to a resting phase, the numbers of hatched E. affinis were log-linearly negatively related to density of M. affinis. An increase of M. affinis density from 1,000 to 5,000 individuals m⁻², normal field densities, reduced the hatching by 60–70%. The negative impact was mainly exerted during the hatching phase, suggesting predation on, burial of or physical injury of hatching nauplii or eggs in a late development stage as likely mechanisms. Also, the number of B. longispina maritima that hatched was reduced by M. affinis during the hatching phase, but no clear relation to density of M. affinis could be identified. The results show that M. affinis can reduce recruitment to zooplankton from benthic resting eggs. Such impact by the benthos on resting stages of zooplankton is therefore a potentially significant link between the benthic and pelagic systems. Received: 10 August 2000 / Accepted: 13 November 2000     

Population genetics of the swimming crab<Emphasis Type="Italic"> Callinectes bellicosus</Emphasis> (Brachyura: Portunidae) from the eastern Pacific Ocean

The population genetics and historical demography of the swimming crab Callinectes bellicosus from the eastern Pacific were assessed using mitochondrial DNA (mtDNA) sequences from portions of the cytochrome c oxidase subunit I (COI) and cytochrome b (Cytb) genes. Analysis of molecular variance of sequence data from crabs collected from nine localities, ranging from the upper to lower Gulf of California and the outer coast of the Baja California peninsula, revealed an absence of population structure, suggesting a high level of gene flow over a wide geographic area. Maximum-likelihood estimates of long-term effective population size obtained with the program FLUCTUATE, in addition to highly significant values obtained from neutrality tests (Tajimas D, Fu and Lis D, and Fus F_S) and mismatch analysis, are consistent with a population expansion dating to the Pleistocene epoch. Phylogenetic analysis of C. bellicosus sequences using both neighbor-joining and Bayesian methods revealed a widely distributed subclade (clade II) cryptically embedded at low frequency in the main (clade I) population. Although sequence divergence between the two clades was low (1.1% COI; 0.6% Cytb), statistical support for the split was high. The Kimura-2-parameter genetic distance between C. bellicosus and the sympatric and morphologically similar C. arcuatus was high (d=0.17) and similar to the genetic distance between C. bellicosus and the allopatric C. sapidus from the western Atlantic (d=0.18), suggesting an ancient (Miocene) divergence of C. bellicosus and C. arcuatus.Communicated by P.W. Sammarco, Chauvin     

Otolith age validation and growth-rate variation in flyingfish (Hirundichthys affinis) from the eastern Caribbean

A study of otolith aging and growth-rate variation in the flyingfish Hirundichthys affinis (Günther) was conducted in the eastern Caribbean (10–16°N; 58–62°W) in 1987–1989. Daily otolith-increment formation was validated in laboratory-reared larvae, confirming the usefulness of otolith-increment counts for age determination of H. affinis juveniles (<150 mm fork length, FL). A mark-recapture programme to validate increment formation in wild adults was unsuccessful due to tetracycline-linked mortality and insufficient tetracycline uptake in slow-growing adult otoliths. A von Bertalanffy growth curve fitted to juvenile size-at-age data gave preliminary growth-curve parameters of t ₀=2.85 d and k=0.00854 on a daily basis, with an asymptotic length, L, of 245 mm FL, for eastern Caribbean flyingfish. Juvenile growth rate in H. affinis is sensitive to spatial and temporal variation in temperature. Growth rates were higher where sea-surface temperatures were higher, and were higher for juveniles hatched in warmer months (April–July) than in colder months (November–March). Growth rates were also higher near islands than at more oceanic locations. Variation in juvenile growth rates may influence the spatial and temporal variation in spawning frequency observed in H. affinis.     

Seasonal variation of membrane fluidity of the naturally acclimatized Baltic Sea amphipods Gammarus spp. and Monoporeia affinis

The membrane fluidity of the Baltic Sea crustaceans Gammarus spp. and Monoporeia affinis was studied in different seasons. Gammarus spp. were collected at a location with stable salinity and with temperature fluctuations from about 0 to 20 °C, and M. affinis at a deep location with stable salinity and a constant low temperature of about 1.5 to 4.5 °C. The membrane fluidity was measured from preparations enriched with plasma and mitochondrial membranes employing a fluorescence polarization technique using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a probe. The measurements were carried out without any preceding acclimation of the animals. In Gammarus spp., the membrane fluidity increased in the order: summer animals < autumn animals < spring animals. The differences between seasons were significant, with pronounced homeoviscous adaptation, and correlated well with the water temperature. It is suggested that in Gammarus spp., temperature is the determining factor for membrane fluidity. In M. affinis, the membranes of summer animals were the most fluid, and there was a significant difference only between summer and spring animals. In M. affinis the difference was not connected to the water temperature and no homeoviscous adaptation was noticed. The deep-water M. affinis experience a long period of fresh food deficiency, which probably affects the membrane fluidity. Although there are seasonal differences in fluidities between Gammarus spp. and M. affinis, it is interesting to note that all data obtained from M. affinis settled between the polarization lines of spring and summer Gammarus spp., regardless of the prevailing temperatures. Received: 30 June 1999 / Accepted: 7 June 2000     

Impact of a burrowing deposit-feeder, Monoporeia affinis, on viable zooplankton resting eggs in the northern Baltic Sea

We investigated the effect of different densities of the burrowing deposit-feeding amphipod Monoporeia affinis on the potential for recruitment of zooplankton from benthic resting eggs. Hatching of resting eggs was induced in the laboratory on sliced and resuspended 1-cm depth-sections of sediment cores, collected at six stations in an archipelago area of the Gulf of Bothnia, Baltic Sea. The uppermost 5 cm of the sediment was studied. The most common species that hatched was Eurytemora affinis (Copepoda). Individuals from another copepod genus, Acartia, hatched in significant numbers only in the cores from two stations with low amphipod abundance. Cores from stations with high amphipod densities showed a deeper distribution of emerging E. affinis nauplii compared with stations with few amphipods; the oxidised sediment layer was also deeper at high M. affinis densities than at low. Total (0 to 5 cm strata pooled) number of hatched E. affinis nauplii was independent of amphipod density. This indicates that the effect of M. affinis on E. affinis eggs involves deeper burial due to bioturbation, rather than predation. Decreased benthic recruitment of zooplankton at localities with high M. affinis density is suggested, since more deeply positioned eggs are less likely to hatch. When hatching was induced in intact, non-sliced cores from one station, the number of E. affinis nauplii that hatched was on average 43% of the number that hatched in the upper centimetre of the sliced cores from the same station. This fraction (43%), if applied to the other stations, implied a potential for benthic recruitment of up to 80 000 ind m⁻² for E. affinis. Due to its high abundance, M. affinis is likely to greatly reduce benthic recruitment of zooplankton in this system. Received: 17 September 1999 / Accepted: 23 February 2000     

Growth histories of strombid snails from Bermuda recorded in their O-18 and C-13 profiles

The isotopic ratios ¹⁸O/¹⁶O and ¹³C/¹²C show an annal periodicity in the strombid snails Strombus gigas and S. costatus from Bermuda. S. gigas appears to have a constant displacement of 0.5 from oxygen isotopic equilibrium, whereas S. costatus fractionates the oxygen istopes in accordance with established fractionation relationships. With this tool, the growth in strombid snails during different stage can readily be determined on one and the same snail. A 24.8 cm long S. gigas showed an age of 7, a 19.3 cm long S. costatus of 5, and a 7.8 cm long S. costatus of 2 years. From the annual range in oxygen isotopes, growth restricted to warmer periods of the year is assumed. The abundances of ¹⁸O and ¹³C tend to be positively correlated in adult S. gigas and S. costatus speciments, but were inversely related in a juvenile S. costatus.     

Are there true cosmopolitan sipunculan worms? A genetic variation study within Phascolosoma perlucens (Sipuncula, Phascolosomatidae)

Phascolosoma perlucens is one of the most common intertidal sipunculan species and has been considered a circumtropical cosmopolitan taxon due to the presence of a long-lived larva. To verify whether P. perlucens is a true cosmopolitan species or a complex of cryptic forms, we examined the population structure and demographics of 56 putative P. perlucens individuals from 13 localities throughout the tropics. Analysis of two mitochondrial markers, cytochrome c oxidase subunit I and 16S rRNA, suggests high levels of genetic differentiation between distantly located populations of P. perlucens. At least four different lineages identified morphologically as P. perlucens were distinguished. These lineages are likewise supported by phylogenetic analysis of the two mitochondrial markers and by the haplotype network analysis. Our results suggest that P. perlucens is a case of overconservative taxonomy, rejecting the alleged cosmopolitanism of P. perlucens. However, cryptic speciation also exists in some areas, including a possible case of geminate species across the Isthmus of Panama.     

Structure and function of the stomachless digestive system in three related species of New World silverside fishes (Atherinopsidae) representing herbivory, omnivory, and carnivory

We explored possible diet-related specializations in the digestive tract of stomachless fishes by summarizing the diets, verifying the absence of a stomach, and comparing gut lengths, microvilli surface areas, and activities of five digestive enzymes in four taxa of silversides from southern California coastal waters. For the comparisons, we examined these gut features in Atherinops affinis from both estuarine and kelp-forest habitats, and Atherinopsis californiensis and Leuresthes tenuis from open coastal habitats. A. affinis was found to be primarily herbivorous in estuaries and carnivorous in kelp forests, whereas As. californiensis was shown to be somewhat omnivorous but mainly carnivorous, and L. tenuis strictly carnivorous. Estuarine A. affinis exhibited the longest gut, largest microvilli surface area, and highest amylase and maltase activities, all arguably reflecting responses to an algal diet. In contrast, kelp-forest A. affinis displayed the highest trypsin activity and generally similar microvilli surface areas and aminopeptidase, amylase, and maltase activities to the two other carnivorous taxa. All four taxa showed similar lipase activities that compared closely with published values for other fishes. Taken together, our results reveal striking differences in gut structure and function among the four taxa, but especially between the estuarine and kelp-forest populations of A. affinis. Further studies are required to assess the roles of genetic variation and phenotypic plasticity in explaining the differences in these herbivorous and carnivorous taxa.     

Incipient speciation within a subgenus of rockfish (<Emphasis Type="Italic">Sebastosomus</Emphasis>) provides evidence of recent radiations within an ancient species flock

The high frequency of speciation events associated with species flocks (i.e., radiations of closely related species) provides invaluable insight into the speciation process. Investigations of the speciation process in the marine environment are rare, and therefore, the genetic analysis of the rockfish genus Sebastes, considered an ancient marine species flock, provides an opportunity to investigate this process in the sea. Using both mitochondrial and nuclear markers, we analyzed five closely related species within the rockfish subgenus Sebastosomus. Our goal was to understand the evolutionary history and genetic relationships among species within this group and to provide evidence of recent speciation events within the subgenus. In the genetic analysis of the subgenus, we found different stages of the speciation process, with greater genetic divergences among three of the five species, evidence of recent divergence between two of the five species, Sebastes entomelas and S. mystinus, and significant genetic divergence between two lineages within S. mystinus revealing a signature of incipient speciation. We also found frequency differences of the two S. mystinus lineages among sample locations and found no evidence of introgression between the lineages at the location where both coexist. Although Sebastes is an example of an ancient species flock, this study provides evidence of ongoing speciation within the genus and reveals stages of this process from incipient to distinct species.     

Sinking rates and dissolution of midwater fish fecal matter

The sinking rates of fecal matter from 7 southern California midwater fish species were investigated. Feces were obtained from 162 specimens of Stenobrachius leucopsarus, Triphoturus mexicanus, Leuroglossus stilbius, Lampanyctus ritteri, Argyropelecus affinis and Parvilux ingens, which were collected in the Santa Barbara and San Clemente Basins between 1977 and 1979. In addition, feces obtained from 6 laboratory-maintained specimens of the midwater zoarcid Melanostigma pammelas were used for repeated sinking-rate measurements. The mean of the measured sinking rates for all species was 1.19 cm s^-1 (1 028 m d^-1), which is much higher than the known descent rates of euphausiid and copepod fecal pellets and of most other particulate organic detritus. Dissolution characteristics were also investigated for fecal matter from 4 species collected by the same series of net hauls: S. leucopsarus, T. mexicanus, A. affinis, and Sternoptyx obscura. The release of dissolved organic compounds from this material is low and does not represent a significant output during the relatively short time required to sink through the water column. These findings suggest that midwater fish fecal matter may represent a major source of organic transfer between the pelagic community and the benthos.     

Control of populations of the coral-feeding nudibranch Phestilla sibogae by fish and crustacean predators

Juvenile lesser blue crabs, Callinectes similis Williams, were exposed to a range of salinities for measurement of survival and bioenergetics. Effects of salinity on survival were determined by exposing juvenile crabs to salinity treatments ranging from 0 to 74‰. All crabs survived 21 d of exposure to 5 and 45‰S. The 21 d LC₅₀ values for salinity tolerance (calculated from survival data) were 2.6 and 60.8‰S at low and high salinities, respectively. Energy-budget components and scope for growth were determined for crabs exposed to 2.5, 10, 25, 35 and 50‰S. Energetic absorption rates were highest at 2.5 and 35‰S. Energetic expenditure rates (energy lost to respiration and excretion) were greatest at 2.5‰S, and decreased as salinity increased. Respiration constituted the majority of energetic expenditure at all salinities (92.3% average). Scope for growth was significantly affected by salinity and was highest in crabs exposed to 35‰S. Increased respiration at low salinity may indicate that C. similis incurs greater costs due to osmoregulation. The results of this study indicate that C. similis is capable of surviving and growing in waters with salinities as low as 10‰. Received: 10 January 1997 / Accepted: 11 February 1997     

Sink or swim? Copepod population maintenance in the Columbia River estuarine turbidity-maxima region

Maintenance of estuarine zooplankton populations in large river-dominated estuaries with short residence times has been an intriguing subject of investigation. During three different hydrological seasons, autumn 1990, summer 1991, and spring 1992, we intensively sampled zooplankton populations in the estuarine turbidity maxima (ETM) region of the Columbia River estuary of Oregon and Washington, USA. One of the principal objectives was to investigate retention mechanisms of the predominant zooplankton species, the harpacticoid copepod Coullana canadensis and the epibenthic calanoid copepod Eurytemora affinis. In the ETM, C. canadensis densities mirrored those of turbidity gradients and were almost always greater at the river bed, while E. affinis densities were greater higher in the water column during the flood and lower in the water column during the ebb. Cross-correlation and time-series analyses determined that C. canadensis densities were highly positively correlated with turbidity and that most of the variability was explained by the lunisolar diurnal (K₁) and principal lunar (M₂) tidal components occurring once every 23.93  h and once every 12.42 h, respectively. This indicates that C. canadensis populations are most probably maintained in the estuary through the same near-bottom circulation features that trap and concentrate particles in the ETM. In contrast, densities of the more motile species E. affinis were highly correlated with negative velocities, or ebb tide, and most of the variability in population densities could be explained by the principal lunar tidal component; therefore, we hypothesize that this species is probably vertically migrating on a tidal cycle into different flow layers to avoid population losses out of the estuary. Received: 7 April 1997 / Accepted: 22 April 1997     

Genealogical relationships within and among shallow-water <Emphasis Type="Italic">Ciona</Emphasis> species (Ascidiacea)

In spite of historical and current interest in Ciona intestinalis and its congeners, little is known about evolutionary relationships among the members of the genus Ciona. Here 744-bp sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene are used to examine phylogenetic relationships among three described species (C. intestinalis, C. roulei, C. savignyi) sampled from multiple coastal sites in the Northeast Pacific (CA, USA), Northwest Atlantic (from New Hampshire to Connecticut, USA), Northeast Atlantic (Sweden and The Netherlands), and Mediterranean (Banyuls-sur-Mer, France). The samples were collected in June–October 2005. The COI sequences of Northeast Pacific/Mediterranean (Type A) and Northwest Atlantic (Type B) C. intestinalis differ by ∼12% and C. roulei is nested within Type B C. intestinalis. Ciona savignyi differs from all other haplotypes by 13–16%. A previously undescribed but morphologically distinct Ciona sp. found at the Banyuls-sur-Mer site was >10% divergent from all other haplotypes. Although these data arise from a single gene study, they indicate that further elucidation of species relationships within the genus and of the species’ distributions will be needed if continuing invasions and potential reproductive isolation are to be investigated.     

Some effects of temperature on the growth and metabolic rate of juvenile blue crabs,Callinectes sapidus,in the laboratory

Juvenile blue crabs, Callinectes sapidus Rathbun, were grown in the laboratory at different temperatures, and metabolic-rate determinations were made. Growth is shown to be dependent upon temperature. Crabs kept at high temperatures (34° and 27°C) grow faster than those kept at lower temperatures (13°, 15°, and 20°C). Increase in size per molt is less at higher temperatures than at lower ones. Mortality is directly proportional to temperature between 13° and 34°C and is very high during ecdysis at elevated temperatures. Metabolic rate increases with temperature, but various degrees of acclimation are seen after 4 weeks exposure. No acclimation of general activity to temperature was found. The findings are applied theoretically to crabs living in the region of heated discharge canals of electrical generators: the motile blue crab could extend its growing season without decreasing size at maturity by active selection of thermal surroundings.In part based on a thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science at the University of Florida, USA.     

Temperature and salinity adaptation in the purple shore crab Hemigrapsus nudus: An in vitro physiological study with excised gills

The alkali-soluble polysaccharides of the cell wall from 7 different marine diatoms were shown to contain the monosaccharides rhamnose, fucose, galactose, mannose and xylose. The relative amounts of rhamnose and fucose varied widely from one species to another, from the very rhamnose-rich Chaetoceros affinis to Thalassiosira gravida, where no rhamnose was found. All Chaetoceros species were found to have a high content of rhamnose. Also the proportion of mannose to galactose varied widely from species to species. The observed change in monomer composition from the logarithmic to the stationary growth phase is explained by assuming the alkali-soluble fraction to be a mixture of polysaccharides. The soluble, extracellular polysaccharides from 4 of the diatoms were also investigated. The products from C. affinis and C. curvisetus were homogeneous and composed of only 3 monomers: rhamnose, fucose and galactose. The extracellular polysaccharide composition in all species investigated was quite different from the composition of the cellular alkali-soluble fraction. The ecological aspects of these soluble polysaccharides may prove of considerable interest.     

Survival and bioturbation of the amphipod Monoporeia affinis in sulphide-rich sediments

Laboratory experiments were conducted to investigate the survival rate of Monoporeia affinis in sulphide-rich sediment with oxic overlying water, and the effect of amphipod bioturbation on sulphide and oxygen profiles. As long as the oxygen content in the water is high, the amphipods seem to avoid quite high concentrations (>200 μmol l⁻¹) of sulphide in the sediment by creating microhabitats where sulphide is rapidly oxidised. In cores with amphipods, a decrease of sulphide concentration was found in upper layers, while an increase of sulphide was found in deeper layers. Aggregation of amphipods generated pockets of light-brown sediment, characterised by high oxygen concentrations and no sulphide, and their depth was clearly dependent on amphipod density. This indicates that M. affinis has a potential to recolonise sulphide-rich sediments, devoid of macroscopic life, after the overlying water column has become oxygenated. Received: 13 April 2000 / Accepted: 8 September 2000