Epibenthic Species Research Articles

EXTENDED MATERNAL CARE OBSERVED IN PARALLORCHESTES OCHOTENSIS (AMPHIPODA, GAMMARIDEA, TALITROIDEA, HYALIDAE)

Abstract Several peracarid crustaceans have been shown to engage in extended maternal care for their growing offspring after the juveniles hatch from the brood pouch of the female. In this study, we describe the maternal care of the epibenthic gammaridan Parallorchestes ochotensis Brandt and examine its ecological implications. The juveniles stayed in the female's expanded brood pouch for at least seven weeks after hatching. The duration of extended maternal care of P. ochotensis was comparatively longer and the growth of P. ochotensis juveniles slower than reported for other epibenthic peracarids. The juveniles molted at least twice whilst in maternal care. This species probably has an annual life span, and they reproduce only once a year. In P. ochotensis, maternal care was shown to constrain juvenile growth in the experimental predator-free conditions, contrary to other epibenthic peracarids. Most epibenthic peracarid species with extended maternal care are suspension feeders, but P. ochotensis is an h...

Weighing the evidence of ecological risk from chemical contamination in the estuarine environment adjacent to the Portsmouth Naval Shipyard, Kittery, Maine, USA

In characterizing ecological risks, considerable consensus building and professional judgments are required to develop conclusions about risk. This is because how to evaluate all the factors that determine ecological risk is not well defined and is subject to interpretation. Here we report on the application of a procedure to weigh the evidence of ecological risk and develop conclusions about risk that will incorporate the strengths and weaknesses of the assessment. The procedure was applied to characterize ecological risk of chemical contamination in nearshore areas adjacent to the Portsmouth Naval Shipyard, located at the mouth of the Great Bay Estuary, New Hampshire and Maine, USA. Measures of exposure and effect were used to interpret the magnitude of risk to the assessment endpoints of pelagic species, epibenthic species, the benthic community, eelgrass plants, the salt marsh community, and avian receptors. The evidence of chemical exposure from water, sediment, and tissue and the evidence of biological effects to representative pelagic, epibenthic, benthic, eelgrass, salt marsh, and avian species were weighed to characterize ecological risk. Individual measures were weighted by the quality and reliability of their data and risk was estimated from the preponderance, magnitude, extent, and strength of causal relationships between the data on exposure and effects. Relating evidence of risk to hypothesized pathways of exposure made it possible to estimate the magnitude of risk from sediment and water and express the confidence associated with the findings. Systematically weighing the evidence of risk rendered conclusions about risk in a manner that was clearly defined, objective, consistent, and did not rely solely on professional judgment.

Utilisation of invertebrates discarded from the Nephrops fishery by variously selective benthic scavengers in the west of Scotland

Demersal trawl fisheries generate large quantities of discards which temporarily increase the amount of carrion available to benthic communities and lead to a faster energetic turn- over. This study examines the availability of discarded material to the benthos, assesses consumption times of different items and identifies scavengers attracted to those invertebrates most frequently dis- carded from Clyde Sea Nephrops trawlers. In field and laboratory trials, heavy-shelled dead whelks (Buccinum undatum, Neptunea antiqua) sank faster than softer-bodied species like cephalopods (Allotheuthis subulata, Rossia macrosoma) or echinoderms (Ophiura ophiura, Asterias rubens), mak- ing most discards available to the benthos (at ca. -60 m CD (chart datum)) within minutes after dis- carding. SCUBA and time-lapse camera observations in the Clyde Sea and Loch Sween indicated bait utilisation times between 24 and 48 h. Fast-moving animals like brachyuran crabs were the first to arrive at discard bait piles whose composition mimicked typical discards from the Clyde Sea Nephrops fishery. Bimonthly deployments of traps baited with invertebrate discards in the north of the Clyde Sea showed that A. rubens, followed by Pagurus bernhardus, Liocarcinus depurator and whelks, were the most abundant megafaunal scavengers. Fine-meshed funnel traps deployed inside those creels yielded up to 2819 amphipods per trap, with Scopelocheirus hopei and Orchomene nanus accounting for most of the catch. Together with whelks, A. rubens and Carcinus maenas, O. nanus showed a clear preference for crustacean bait. By contrast, Pagurus bernhardus was more attracted to A. rubens and, in 1 trial, to O. ophiura bait. Traps deployed in the south of the Clyde Sea yielded generally lower numbers and species diversity in the catch, with Nephrops being the most abundant megafaunal scavenger. It showed a preference for L. depurator and conspecific bait. While the results show that a range of epibenthic species readily utilise invertebrates discarded from Clyde Sea Nephrops trawlers, it is unknown to what extent discards subsidise benthic communities as infor- mation on the ecological energetics of the species involved locally is currently lacking.

An assessment of the toxicity of phthalate esters to freshwater benthos. 2. Sediment exposures

Seven phthalate esters were evaluated for their 10-d toxicity to the freshwater invertebrates Hyalella azteca and Chironomus tentans in sediment. The esters were diethyl phthalate (DEP), di-n-butyl phthalate (DBP), di-n-hexyl phthalate (DHP), di-(2-ethylhexyl) phthalate (DEHP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), and a commercial mixture of C7, C9, and C11 isophthalate esters (711P). All seven esters were tested in a sediment containing 4.80% total organic carbon (TOC), and DBP alone was tested in two additional sediments with 2.45 and 14.1% TOC. Sediment spiking concentrations for DEP and DBP were based on LC50 (lethal concentration for 50% of the population) values from water-only toxicity tests, sediment organic carbon concentration, and equilibrium partitioning (EqP) theory. The five higher molecular weight phthalate esters (DHP, DEHP, DINP, DIDP, 711P), two of which were tested and found to be nontoxic in water-only tests (i.e., DHP and DEHP), were tested at single concentrations between 2,100 and 3,200 mg/kg dry weight. Preliminary spiking studies were performed to assess phthalate ester stability under test conditions. The five higher molecular weight phthalate esters in sediment had no effect on survival or growth of either C. tentans or H. azteca, consistent with predictions based on water-only tests and EqP theory. The 10-d LC50 values for DBP and H. azteca were >17,400, >29,500, and >71,900 mg/kg dry weight for the low, medium, and high TOC sediments, respectively. These values are more than 30x greater than predicted by EqP theory and may reflect the fact that H. azteca is an epibenthic species and not an obligative burrower. The 10-d LC50 values for DBP and C. tentans were 826, 1,664, and 4.730 mg/kg dry weight for the low, medium, and high TOC sediments, respectively. These values are within a factor of two of the values predicted by EqP theory. Pore-water 10-d LC50 values for DBP (dissolved fraction) and C. tentans in the three sediments were 0.65, 0.89, and 0.66 of the water-only LC50 value of 2.64 mg/L, thereby agreeing with EqP theory predictions to within a factor of 1.5. The LC50 value for DEP and C. tentans was >3,100 mg/kg dry weight, which is approximately 10x that predicted by EqP theory. It is postulated that test chemical loss and reduced organism exposure to pore water may have accounted for the observed discrepancies with EqP calculations for DEP

An assessment of the toxicity of phthalate esters to freshwater benthos. 1. Aqueous exposures

Tests were performed with the freshwater invertebrates Hyalella azteca, Chironomus tentans, and Lumbriculus variegatus to determine the acute toxicity of six phthalate esters, including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBP), di-n-hexyl phthalate (DHP), and di-2-ethylhexyl phthalate (DEHP). It was possible to derive 10-d LC50 (lethal concentration for 50% of the population) values only for the four lower molecular weight esters (DMP, DEP, DBP, and BBP), for which toxicity increased with increasing octanol-water partition coefficient (Kow) and decreasing water solubility. The LC50 values for DMP, DEP, DBP, and BBP were 28.1, 4.21, 0.63, and 0.46 mg/L for H. azteca; 68.2, 31.0, 2.64, and > 1.76 mg/L for C. tentans; and 246, 102, 2.48, and 1.23 mg/L for L. variegatus, respectively. No significant survival reductions were observed when the three species were exposed to either DHP or DEHP at concentrations approximating their water solubilities.

Occurrence and Effects of Organotins on Adult Common Whelk ( Buccinum undatum) (Mollusca, Gastropoda) in Harbours and in a Simulated Dredging Situation

Transplanted common whelk ( Buccinum undatum) (Mollusca, Gastropoda) accumulated fairly high levels of organotins (tributyltin (TBT) and triphenyltin (TPT)) during exposure in three harbours with different TBT contamination. This did not though lead to an increase in imposex frequency in the adult females studied. Simulating harbour dredging in an experiment using suspended sediment from one of the harbours only resulted in a low concentration of TBT in the tissues of the common whelk and subsequently no changes in the occurrence and degree of imposex. The common whelk seemed to receive the main part of TBT from the water column and the limited bioaccumulation in the experiment indicates that desorption of TBT from the suspended sediment was slow. After TBT has been totally banned, dredging of contaminated sediments will cause increased exposure of the biota to TBT. Due to slow desorption the increase may however, be slight and temporary to pelagic and epibenthic species unless the settled particles are resuspended.

δ15N and δ13C Measurements of Antarctic Peninsula Fauna: Trophic Relationships and Assimilation of Benthic Seaweeds1

SYNOPSIS. Measurements of d 13 C, d 15 N, and C/N for a variety of Antarctic peninsula fauna and flora were used to quantify the importance of benthic brown algae to resident organisms and determine food web relationships among this diverse littoral fauna. d 13 C values ranged from216.8‰ for benthic algal herbivores (limpets) to 229.8‰ for the krill, Euphausia superba; the average pooled value for brown macroalgae, including their attached filamentous diatoms, was220.6‰. There was no correlation between biomass d 13 Co rd 15 N with C/N content, and consequently both d 13 C and d 15 N values were useful in evaluating trophic relationships. d 15 N values of the fauna ranged from 3.1 to 12.5‰, with lowest values recorded in suspension feeders (e.g., bryozoans) and highest values in Adelie penguins (12.5‰) collected in 1989. The comparatively lower d 15 N value for a Chinstrap penguin (6.9‰) collected in 1997 is attributed to the different dietary food sources consumed by these species as reflected in their respective d 13 C values. Significant amounts of benthic macroalgal carbon is incorporated into the tissues of invertebrates and fishes that occupy up to four trophic levels. For many benthic and epibenthic species, including various crustaceans and molluscs, assimilation of benthic algal carbon through detrital pathways ranges from 30 to 100%. Consequently, the trophic importance of benthic brown algae may well extend to many pelagic organisms that are key prey species for birds, fishes, and marine mammals. These data support the hypothesis that benthic seaweeeds, together with their associated epiphytic diatoms, provide an important carbon source that is readily incorporated into Antarctic peninsula food webs.

Bacterial abundance and biomass in response to organism-generated habitat heterogeneity in deep-sea sediments

Deep-sea sediments beneath double-ridged crawling trails and around two sessile epibenthic species, the sea anemone Bathyphellia margaritacea Danielssen, 1890 and the demosponge Thenea abyssorum Koltun, 1959, were investigated to test whether they support a bacterial colonisation significantly higher than that of nearby control sediments. The centimetre-scale features and the control sites with a virtually undisturbed sediment surface were sampled in two basin-like depressions in Fram Strait (Molloy Deep, 5552 m; Hayes Deep, 3668 m), and on the eastern Greenland continental rise (3139 m) using a Remotely Operated Vehicle. The uppermost 5 cm-thick layer of the sediment around the two species and beneath the trails contained a significantly higher total bacterial biomass (TBB) than the control sediments. The higher TBB values resulted either from higher total numbers of sedimentary bacteria (TBN), from a higher mean biomass per cell (MBC), or both. Sediments beneath the crawling trails were inhabited by significantly more bacteria than the control sediment. The mean cell biomass of the bacteria did not differ. The TBN around the sea anemone B. margaritacea and in control samples were almost in the same range; the MBC around the anemones, however, was significantly higher than in the control sediments. The higher TBB in the sediment around the sponge T. abyssorum resulted from higher values of both TBN and MBC. Our results confirmed that small epibenthic species and crawling trails sufficiently modify the surrounding sediment-seawater interface to affect the abundance and biomass of sediment-associated biota. The biogenic structures locally increase bacterial colonisation at the sediment-water interface and thus potentially increase habitat heterogeneity for the smallest benthic organisms.

Effects on benthic scavengers of discards and damaged benthos produced by the beam-trawl fishery in the southern North Sea

The beam-trawl fishery for flatfish produces large amounts of dying discards as well as damaged and disturbed benthos. The importance of these food sources to scavenging benthic species was investigated. To identify epibenthic species showing scavenging behaviour and to detect their food preferences, traps (370 overall) baited with different kinds of carrion (fish, crustaceans, molluscs, echinoderms, polychaetes) were deployed at 14 locations in the southern North Sea. Liocarcinus holsatus, Pagurus bernhardus, Asterias rubens, ophiurids, and small gadoids were the main active scavengers feeding on different kinds of food, while lyssianid amphipods (Orchomene nanus, Scopelocheirus hopei) fed mainly on crustacean carrion. Estimated attraction areas were largest for gadoids, hermit crabs, and swimming crabs. Immigration of fish and swimming crabs into experimentally trawled areas was observed by sampling repeatedly in a trawled strip. Differences in the response to trawling (feeding activity, food niche breadth, and resource partitioning) between selected fish species are described. Limanda limanda, Pleuronectes platessa, Merlangius merlangus, Callionymus lyra, and Eutrigla gurnardus all showed strong responses, using different feeding strategies. In situ clearance rates of dead discarded fish exposed on the sea floor were estimated. Discards as well as moribund benthos were consumed within a few days. The balance between the amount of food materials produced by beam-trawl fishery and the amount of food consumed by potential scavengers was translated in a model of the food flows as mobilized by beam trawling. In general, the direct importance of the additional food resource for populations of scavengers is considered to be relatively small. However, the importance may be relatively larger for scavenging fish than for invertebrates. It is estimated that after a single beam trawling about 1.27 g m 2 ash-free dry biomass, or 6% to 13% of the annual secondary production of macrobenthos per unit area, would suddenly become available to scavengers and to the detritus food chain. It is suggested that beam trawling leads to shortcuts in trophic relationships and therefore may enhance secondary production. 2000 International Council for the Exploration of the Sea

Antarctic notothenioid fishes as subjects for research in evolutionary biology

Antarctica is a continental island and the waters of its shelf and upper slope are an insular evolutionary site. The shelf waters resemble a closed basin in the Southern Ocean, separated from other continents by distance, current patterns and subzero temperatures. The benthic fish fauna of the shelf and upper slope of the Antarctic Region includes 213 species with higher taxonomic diversity confined to 18 families. Ninety-six notothenioids, 67 liparids and 23 zoarcids comprise 45%, 32% and 11% of the fauna, a combined total of 88%. In high latitude (71–78°S) shelf areas notothenioids dominate abundance and biomass at levels of 90–95%. Notothenioids are also morphologically and ecologically diverse. Although they lack a swim bladder, the hallmark of the notothenioid radiation has been repeated diversification into water column habitats. There are pelagic, semipelagic, cryopelagic and epibenthic species. Notothenioids exhibit the disproportionate speciosity and high endemism characteristic of fish species flock. Antifreeze glycopeptides originating from a transformed trypsinogen gene are a key innovation. It is not known when the modern Antarctic shelf fauna assumed its current taxonomic composition. A late Eocene fossil fauna was taxonomically diverse and cosmopolitan. There was a subsequent faunal replacement with little carryover of families into the modern fauna. Basal notothenioid clades probably diverged in Gondwanan shelf locations during the early Tertiary. Dates inferred from molecular sequences suggest that phyletically derived Antarctic clades arose 15–5 m.y.a.

Spatial patterns and seasonality in the epibenthic communities of the Westerschelde (Southern Bight of the North Sea)

Beamtrawl samples were taken monthly between January 1988 and December 1989 in 14 subtidal stations along the longitudinal axis of the Westerschelde Estuary. The estuary harboured high densities of epibenthic species (total average of 2250 ind 1000 m−2). Only 37 fish species were recorded and three mobile macroinvertebrate species were quantified. Seventeen epibenthic species were common, only eight of which were very abundant. An overall dominance of the brown shrimp Crangon crangon was noted. The near absence of anadromous and freshwater species was correlated with the low oxygen concentrations upstream the Dutch–Belgian border. The epibenthic species could be divided into a polyhaline and a mesohaline community along the main salinity–oxygen–turbidity gradients of the estuary. The mesohaline zone was characterized by higher densities and biomasses for shrimps, gobies and flatfish. The spatial structure in the epibenthic community of the polyhaline zone was more influenced by the watermasses from the sea and inflowing channels, and was correlated with the degree of exposure (current velocities and tides). A classification is proposed, based on the season in which the epibenthic species occur in the estuary, and on their life stages and abundances during that period. The monthly data demonstrate that while the eight abundant epibenthic species were generally present throughout the year (summer or winter resident), the majority tended to appear in the Westerschelde at varying times (summer, winter or bimodal) and often remained in large numbers (nine common species) for only a short time. The fact that mainly juveniles were recorded in the higher density-classes, suggests that the Westerschelde Estuary still acts as a nursery area for many epibenthic species.

Nervous and sensory system correlates of an epibenthic evolutionary radiation in antarctic notothenioid fishes, genus Trematomus (Perciformes; Nototheniidae).

The perciform suborder Notothenioidei consists of 120 species, with 94 confined to the Antarctic Region of the Southern Ocean. On the Antarctic shelf, this phyletic radiation has been accompanied by a substantial morphological and ecological diversification towards a pelagic existence. For example, the primarily benthic genus Trematomus contains an epibenthic radiation that includes T. loennbergii, T. lepidorhinus, and T. eulepidotus. By comparing these epibenthic species with three congeneric benthic species (T. scotti, T. pennellii, and T. bernacchii) we tested three null hypotheses regarding brain variation in Antarctic trematomids: 1) that there is no difference in brain morphology among the six species; 2) that phylogenetic and ecological factors do not influence brain morphology; and 3) that peripheral sensory structures do not influence brain morphology. We rejected each of these hypotheses, leading us to conclude that Trematomus brains vary interspecifically, between benthic and epibenthic species, and with a species' depth distribution. Further, we conclude that brain variation is correlated with differences in peripheral sensory systems and motor activity. Specifically, epibenthic Trematomus have larger percentages of their brain volume devoted to lateral line mechanoreceptive and motor (cerebellar) structures. Species living at greater depths have low ratios of cones:rods in the retina and larger olfactory structures.

Feeding ecology of juvenile flatfishes of the surf zone of a sandy beach

Prey items of 0‐ and 1‐group plaice Pleuronectes platessa, sole Solea solea, brill Scophthalmus rhombus, turbot S. maximus and dab Limanda limanda of the surf zone of a Belgian sandy beach, included hyperbenthic (e.g. mysids), endobenthic (e.g. polychaetes) and epibenthic (e.g. shrimps) species. Little dietary overlap was observed. If diet overlap did occur, it mainly involved prey species that are dominant in the surf zone of Belgian beaches, such as shrimps and mysids. These results suggest an opportunistic utilization by flatfish of the available food resources in surf zone ecosystems. Also, two strategically different feeding habits could be distinguished between the five flatfish species. Turbot and brill mainly fed on large, highly mobile prey (e.g. fish, mysids) and had a rather narrow prey spectrum, whereas plaice, dab and sole ate more benthic prey (e.g. polychaetes) and had a broader prey spectrum.

Influence of near-bottom environmental conditions on the structure of bathyal macrobenthic crustacean assemblages from the Capbreton canyon (Bay of Biscay, NE Atlantic)

Sled and box-corer samplings were performed at two sites in the Capbreton canyon in order to appreciate the influence of near-bottom environmental conditions on the structure of their macrobenthic communities (crustaceans). Although located at similar depths (ca 1 000 m), these two sites were characterised by different physicochemical conditions at the sediment-water interface, probably related with the 000 m), these two sites were characterised by different physicochemical conditions at the sediment-water interface, probably related with the morphology of the submarine valley (reduced environment, oxygen depletion and stagnation of bottom water at site A; normal oceanic conditions on the near-bottom environment of site B). The analysis of the collected fauna revealed a low similarity between the two sites, mainly due to the unusual dominance of three epibenthic species in sled samples from site A: the amphipod Bonnierella abyssorum, the tanaid Apseude spinosus and the isopod Arcturopsis giardi. Due to their apparent rarity or absence in adjacent non-canyon communities, such epibenthic crustaceans may be considered as canyon indicator species able to exhibit abundant populations within the peculiar confinement arca of this canyon.

Distribution, diversity and abundance of epibenthic fauna in the North Sea

The assemblages of attached and freeliving epibenthic species in the North Sea are described, based on analysis of samples collected with a small beam trawl. Clustering of survey sites based on the presence or absence of attached species indicated that three regions had characteristic assemblages: the northern North Sea, the central North Sea from 55 to 57°N and the southern North Sea. Clustering of sites based on counts of free-living epibenthic species also revealed that the sites formed three major groups but these corresponded to regions in the north-east North Sea, the northern and western central North Sea and the southern and eastern central North Sea. Species which contributed most to the similarity within and dissimilarity between groups were identified. The environmental factors which best accounted for the grouping of sites were depth, winter temperature and the temperature difference between winter and summer for attached species and depth and the temperature difference between winter and summer for free-living species. The species richness of attached and free-living epibenthic species was higher in the central and northern North Sea than in the south. The number of abundant (Hill's N1) and very abundant (Hill's N2) free-living species also increased from south to north.

Duration of Extended Parental Care in Marine Amphipods

ABSTRACT Several peracarid species provide parental care for their growing offspring after these have left the brood pouch of the female. In this study, I examined the duration of extended parental care in 3 soft-bottom dwelling amphipod species: the epibenthic suspension feeder Dyopedos monacanthus(Podoceridae), the burrow-dwelling filter-feeder Leptocheirus pinguis (Aoridae), and the burrow-dwelling deposit-feeder Casco bigelowi (Melitidae). Juvenile D. monacanthus remained on the mud whip of their mother for time periods of 10-20 days, maximally 27 days. Many juveniles left their mother before a second clutch was released onto her mud whip, indicating that factors other than the appearance of a second clutch limit the duration of care for the first clutch of juveniles. Juvenile L. pinguis left the burrow of their mother in distinct batches, usually after a molting event. Some juveniles remained in the burrow of their mother for 40-60 days. Juvenile C. bigelowi commonly remained in the burrow of their mother for >80 days, and departed over a period that lasted 20-40 days until all juveniles had left. A literature review revealed that in many epibenthic peracarids with extended parental care, juveniles usually remain with their mothers for about 3 weeks. Females of species that carry their offspring during parental care usually do not produce a second brood while carrying one brood, whereas females that do not carry but guard their offspring often produce a second brood while caring for the first brood. Duration of extended parental care is much more variable in tube-/burrow-dwelling species, lasting from minutes in some species up to 3 months in others. It is concluded that tube-/burrow-dwelling species have a higher potential for long-lasting (»20 days) extended parental care than epibenthic species. Ecological constraints, such as availability of space and food, predation, disturbance, and competition, are discussed as factors limiting the duration of extended parental care. It is hypothesized that the potential for extended parental care is high in marine peracarids, but advanced social behavior is restricted to species that are living in dwellings of biotic origin.

NEW GENUS OF AEGISTHIDAE (COPEPODA: HARPACTICOIDA) FROM HYDROTHERMAL VENTS ON THE GALAPAGOS RIFT

ABSTRACT Both sexes of Andromastax muricatus, new genus, new species (Copepoda: Harpacticoida: Aegisthidae), are described from a hydrothermal vent on the Galapagos Rift in the eastern Pacific. This epibenthic species represents the most primitive aegisthid known to date, displaying several plesiomorphic character states in the cephalosomic appendages and in P5 and P6. The new species shares some characters with the imperfectly described Aegisthus spinulosus. which is removed from Aegisthus and placed here as a species incertae sedis in the Aegisthidae. The basic setal pattern on the caudal rami in the Aegisthidae is reconsidered and the different degrees of atrophy of the mouthparts in the nonfeeding males are discussed. It is postulated that the family evolved from an epi- or hyperbenthic ancestral stock and that the colonization of the open pelagic environment by Aegisthus is secondary.

Distribution, standing stock, growth, mortality and production of Strongylocentrotus pallidus (Echinodermata: Echinoidea) in the northern Barents Sea

The regular sea urchin, Strongylocentrotus pallidus (G.O. Sars, 1871), is a widespread epibenthic species in high-Arctic waters. However, little is known about its distribution, standing stock, population dy- namics and production. In the northern Barents Sea, S. pallidus was recorded on seabed still photographs at 10 out of 11 stations in water depths of 80-360 m. Mean abundances along photographic transects of 150-300 m length ranged between <0.1 and 14.7 ind. m )2 yielding a grand average of 3.6 ind. m )2 . The small-scale distri- bution along the transects was patchy, with densities varying from nil to an overall maximum of 25.5 ind. m )2 , and exhibited a significant relation to the number of stones present. Sea urchin test diameters, measured on scaled photographs, extended from 7 to 90 mm. Median values at single stations varied from 14 to 46 mm, showing a significant inverse relationship to water depth. Biomass, estimated by combining photo- graphic abundances, size frequencies and a size-mass function established with trawled specimens, ranged between <0.1 and 3.0 g ash-free dry mass m )2 , aver- aging about 1.0 g ash free dry mass m )2 . An analysis of skeletal growth bands in genital plates was carried out with 143 trawled individuals ranging in test diameter (D) from 4 to 48 mm. Assuming these bands to represent annual growth marks, the ages of the specimens ana- lysed ranged between 3 and 42 years. A von BertalanAy function was fitted to size-at-age data to model indi- vidual growth pattern (D¥ a 102.3 mm, k a 0.011 year )1 ,t 0 a 0.633 year). The annual mortality rate Z of the population in the northern Barents Sea was esti- mated from a size-converted catch curve to be 0.08 year )1 . Applying the weight-specific growth rate method, the average P/B ratio and the mean annual production of this population were estimated as 0.07 year )1 and 0.076 g AFDM m )2 year )1 , respectively. In conclusion, S. pallidus is characterized by slow growth, low mor- tality, high longevity and low productivity. Because of its relatively high biomass, it is considered to contribute significantly to total benthic standing stock and carbon flux in the study area.

Morphology of the brain and sense organs in the snailfish Paraliparis devriesi: neural convergence and sensory compensation on the Antarctic shelf.

The Antarctic snailfish Paraliparis devriesi (Liparidae) is an epibenthic species, inhabiting depths of 500-650 m in McMurdo Sound. Liparids are the most speciose fish family in the Antarctic Region. We examine the gross morphology and histology of the sense organs and brain of P. devriesi and provide a phyletic perspective by comparing this morphology to that of four scorpaeniforms and of sympatric perciform notothenioids. The brain has numerous derived features, including well-developed olfactory lamellae with thick epithelia, large olfactory nerves and bulbs, and large telencephalic lobes. The retina contains only rods and exhibits a high convergence ratio (82:1). Optic nerves are small and nonpleated. The tectum is small. The corpus of the cerebellum is large, whereas the valvula is vestigial. The rhombencephalon and bulbospinal junction are extended and feature expanded vagal and spinal sensory lobes as well as hypertrophied dorsal horns and funiculi in the rostral spinal cord. The lower lobes of the pectoral fins have taste buds and expanded somatosensory innervation. Although the cephalic lateral line and anterior lateral line nerve are well developed, the trunk lateral line and posterior lateral line nerve are reduced. Near-field mechanoreception by trunk neuromasts may have been compromised by the watery, gelatinous subdermal extracellular matrix employed as a buoyancy mechanism. The expanded somatosensory input to the pectoral fin may compensate for the reduction in the trunk lateral line. The brains of P. devriesi and sympatric notothenioids share well-developed olfactory systems, an enlarged preoptic-hypophyseal axis, and subependymal expansions. Although the functional significance is unknown, the latter two features are correlated with habitation of the deep subzero waters of the Antarctic shelf.

Living benthic foraminifers from the central Arctic Ocean: faunal composition, standing stock and diversity

Fifty short sediment cores collected with a multiple corer and five box cores from the central Arctic Ocean were analysed to study the ecology and distribution of benthic foraminifers. To work out living faunal associations, standing stock and diversity, separate analyses of living (Rose Bengal stained) and dead foraminifers were carried out for the sediment surface. The size fractions between 63 and 125 μm and >125 μm were counted separately to allow comparison with former Arctic studies and with studies from the adjacent Norwegian–Greenland Sea, Barents Sea and the North Atlantic Ocean. Benthic foraminiferal associations are mainly controlled by the availability of food, and competition for food, while water mass characteristics, bottom current activity, substrate composition, and water depth are of minor importance. Off Spitsbergen in seasonally ice-free areas, high primary production rates are reflected by high standing stocks, high diversities, and foraminiferal associations (>125 μm) that are similar to those of the Norwegian–Greenland Sea. Generally, in seasonally ice-free areas standing stock and diversity increase with increasing food supply. In the central Arctic Ocean, the oligotrophic permanently ice-covered areas are dominated by epibenthic species. The limited food availability is reflected by very low standing stocks and low diversities. Most of these foraminiferal associations do not correspond to those of the Norwegian–Greenland Sea. The dominant associations include simple agglutinated species such as Sorosphaerae, Placopsilinellae, Komokiacea and Aschemonellae, as well as small calcareous species such as Stetsonia horvathi and Epistominella arctica. Those of the foraminiferal species that usually thrive under seasonally ice-free conditions in middle bathyal to lower bathyal water depth are found under permanently ice-covered conditions in water depths about 1000 m shallower, if present at all.