South Georgia, an extremely isolated island within the Antarctic Convergence, was covered by an extensive icecap until ~10,000 years ago. In consequence the depauperate intertidal fauna is of recent origin and consists almost entirely of brooders or direct developers which probably arrived as a result of rafting. Environmental conditions between the tidemarks are comparable with northern Norway and Greenland, so the absence of mussels and barnacles is due to isolation from the nearest feasible sources of colonization (the Falkland Islands and Magellan), and not to a hostile environment. Intertidal animals (eight species studied) have median upper lethal temperatures that are positively and linearly related to maximum height of distribution on the shore. Thermal niche width (median upper lethal temperature minus median lower lethal temperature) is also positively correlated with maximum height of distribution on the shore with species below mid-tide level having narrow niches in contrast to species above mid-tide level that have wide niches. There is no relationship between freezing resistance and position on the shore. Salinity and desiccation tolerances were also greater in animal species from the upper shore than in those from the lower shore. In the case of those species also studied elsewhere (Lasaea rubra (Mollusca: Bivalvia); Nacella condnna (Mollusca: Gastropoda) and Tigriopus sp. (Crustacea: Copepoda)), evidence is presented to show that no special adaptation is exhibited by South Georgian animals, and that upper zonation limits are controlled primarily by physical tolerance. This is particularly marked in the case of N. condnna which has similar thermal tolerances on the Antarctic Peninsula, on Signy Island and at South Georgia; in consequence it can only inhabit the extreme lower shore at South Georgia, yet penetrates to mid-tide level at Signy Island.

The geographic and vertical distribution in the world oceans of species of Boreomysis has been summarized by Mauchline & Murano (1982). Various authors including Birstein & Tchindonova (1958) discussed the vertical distribution of abyssal Boreomysis species in the Pacific Ocean. Relatively little is known about Atlantic populations of Boreomysis at depths >2000 m, though there have been a few reports of occurrences in abyssopelagic zones (Nouvel, 1942, 1943; Tattersall & Tattersall, 1951; Lagardère & Nouvel, 1980; Lagardère, 1985; Hargreaves, 1985). The aim of this paper is to present distribution data on five lesser-known species of Boreomysis from depths >2000 m in the north-eastern Atlantic Ocean at ~30° -42°30′N and to describe in more detail, aspects of their morphology.

Vertical changes in density, size structure and shell shape of Lasaea undulata (Bivalvia: Galeommatoidea) inhabiting intertidal mussel beds were studied at Wakayama Prefecture, Japan. At the study site, where two mytilids Septifer virgatus and Hormomya mutabilis formed vertically contiguous mussel beds, Lasaea density decreased downshore within the S. virgatus bed of the upper and mid zones. Few individuals were found within the H. mutabilis bed of the lower zone. Multiple linear regression analysis revealed that shore height was the only factor which showed a significant, positive correlation with density. Size structure differed between the upper and lower parts of the S. virgatus bed, suggesting that reproductive periods or growth rates of L. undulata differed with shore height. Prodissoconch length and shell shape were also different among shore heights. Number, size and shell shape of juveniles brooded within parents indicated that this species releases its young as non-planktotrophic, crawl-away juveniles. There was no significant difference in density of recruits between artificial mussel clumps of S. virgatus and H. mutabilis within enclosure cages, and no specific association was detected between L. undulata and either of the two mussel species.

A description is provided of the large-scale spatial distribution of the diversity of the benthic macrofauna in the eastern English Channel. Data from the oceanographic cruises of the RCP (Recherche Coopérative sur Programme) Benthos de la Manche Research Programme were obtained during the summers of 1971 to 1975. A total of 707 samples were analysed.

Diversity of each sample was measured by means of the species richness (i.e. the total number of species present), the Shannon-Weaver diversity index and Pielou's evenness index. Diversity values were plotted for all 707 oceanographic stations in the area, following a smoothing procedure. Large-scale spatial trends of diversity of the benthic macrofauna were analysed in relation to sediment and species assemblage distribution, but no spatial correlation was found between the two factors. These results indicate that mechanisms affecting large-scale spatial distribution of the diversity are different from those acting on a smaller scale. The role of the hydro-sedimentary processes acting at the geographic scale of the eastern English Channel as presumptive causes of this large-scale pattern of the macrobenthic diversity is discussed.

From 1989–1992, at quarterly intervals, the National Rivers Authority (NRA) (Thames Region) Thames Estuary Benthic Programme sampled 28 sites within the estuary for benthic macroinvertebrates; meiofauna samples were also taken for the first year. At one subtidal site, situated off Canvey Island, over 200 invertebrate species over the survey period from a sample area of 4·4 m2 were recorded. This species richness was far higher than surrounding sites, including those further out into the North Sea. The most important groups at this site were Nematoda (77 spp.), Crustacea (46 spp.) and Polychaeta (40 spp.) and a species capture curve for macroinvertebrates continued to rise after 44 day grabs. The mean biomass of the site (248 g wet weight /m2) was 20 times that of any other site in the outer estuary. The substratum at the site was highly heterogeneous, yet comparatively stable due to its situation at the base (>20 m depth) of a man-made shipping channel, the provision of a large number of niches perhaps explaining the high biodiversity. The anthropogenic influence on a naturally low biodiversity area emphasises the importance of these ecosystems when considering the conservation of global biodiversity. Methods to determine the relative importance of ecosystems are discussed.

Breeding and population statistics were assessed from February 1993 to September 1995 in a mixed population of the mudsnails Hydrobia neglecta and H. ulvae in the intertidal zone of a macrotidal bay on the Atlantic coast of Brittany, France. The biology of H. neglecta in the mixed population was identical to that found earlier for the same species when living allopatrically elsewhere in the bay, and was also that generally characterizing directly-developing species of Hydrobia that occur in coastal lagoons. The population of the larviparous H. ulvae also showed various features otherwise typifying lagoonal populations of this species: very high juvenile mortality, repeated failure of whole cohorts to recruit, and an age structure dominated by large and relatively old individuals. The number of eggs per capsule was normal for an intertidal H. ulvae population but the number of capsules laid was remarkably low. Why both species should behave in this intertidal marine habitat as if it were lagoonal is unknown. The failure of the cohorts of H. ulvae deriving from spring eggs in the bay may help explain why the majority of lagoonal populations of this species are dominated by old mudsnails and show negligible recruitment. There was no evidence of competitive displacement of H. neglecta by H. ulvae in spite of received wisdom that H. ulvae is the competitive dominant under fully marine conditions; mortality of H. ulvae was more than three times that experienced by H. neglecta regardless of age of the snails.

Estimations of the brooding and larval developmental periods of the callianassid ghost shrimp, Callianassa japonicu Ortmann (Decapoda: Thalassinidea), under field conditions, were made on an intertidal sandflat in western Kyushu, Japan, during the breeding seasons (June-October) of 1992–1994. Females bearing eyed embryos were able to deposit a further batch of eggs 1–5 d after releasing larvae, and it is concluded that such egg deposition was preceded immediately by mating. Based on rearing experiments carried out in the field, the brooding period was found to occupy between 13 and 22 d during June to October, at pore water temperatures of 20.5-27.5°C and salinities of 33.0–34–5‰, a shorter period than those reported for seven other callianassid species. Based on temporal changes in the densities of larvae released by females and newly-settled juveniles on the sandflat, time-lags between the release and settlement events suggested the period of planktonic development with six zoeal stages and the 1st post-larval stage to range from 20 to 25 d during mid-June to mid-August, at water temperatures of 18.5-24.5°C and salinities of 32.0–35.0‰. This is the second shortest larval period among those reported for seven other callianassid species that have five or six zoeal stages.

Physiological processes involved in energy acquisition by the filter-feeding bivalve Cerastoderma edule (L.) (Mollusca: Bivalvia) were quantified under naturally fluctuating feeding conditions imposed by tidal cycles in the Bay of Marennes-Oleron. Physiological measurements were performed during two neap and two spring tidal cycles in order to cover a wide range of seston concentrations (TPM = 15–95 mg I-1). The main effect exerted by tides on the food supply was the resuspension of bottom sediments of low organic content, leading to a strong ‘dilution’ of suspended organic matter.

Although filtration rate was found to increase with seston concentration, ingestion rate was strictly regulated by means of pseudofaeces production. Selection efficiencies for chlorophyll a (SEchl), overall organic matter (SE0), carbon (SEC) and nitrogen (SEN) were estimated and related to dietary descriptors. The following ranking was found for the efficiency with which different substrates were selected: SEchl>SEN>SEo>SEc. Absorption efficiency was found to depend on the organic content of ingested matter according to an exponential saturating function. Observed differences between carbon and nitrogen absorption efficiency were not statistically significant. Absorption rate was kept fairly constant through the wide range of seston concentrations and qualities.

A global study of latitudinal gradients in biodiversity of marine shallow-water, motile epifauna of hard substrata has been initiated by Plymouth Marine Laboratory and the International Association of Meiobenthologists. It is based on the use of artificial substratum units (ASUs) consisting of four pan-scourers and emphasizes the standardization of habitat type and complexity, sample area, sampling strategies, sample processing and analysis. Non-comparability of these factors has invalidated some of the few previous studies on global patterns in biodiversity of marine benthic communities which are reported in the literature. A list of sampling locations and participating research organizations is given along with some preliminary results from one location (south-west England).

A new behavioural bioassay system has been used to examine chemical communication in the crab Carcinus maenas (Crustacea: Brachyura) and has demonstrated the sexually and temporally specific nature of a putative sex pheromone. Mature premoult and postmoult females evoked sexual behavioural responses from receptive male crabs. No response was obtained when intermoult female and premoult and postmoult male crabs were tested. Postmoult females continued to be chemically attractive to male crabs with a similar intensity to that of late premoult females for >8 d following moulting, and then with a reduced intensity for >14 d. Male C. maenas successfully entered copula with females >13 d after the female moult.

Five, possibly six, north European species are confirmed in the prosobranch genera Rissoa and Pusillina: R. parva (Da Costa); R. lilacina Récluz; R. membranacea (Adams) (types A & B); P. inconspicua (Alder) and P. sarsi (Lovén).

The five species differ ecologically in salinity tolerances, with R. membranacea and P. sarsi being the most tolerant and regularly occurring at salinities of 7–10%0, while R. parva, R. lilacina, and P. inconspicua tolerate salinities down to 20%0 (for shorter periods 15%0). There are also differences in the ability to survive occasional, short exposures to highly reduced salinity with 50% survival for R. membranacea after 80 h; R. lilacina, 30 h; P. sarsi, 25–30 h; and for P. inconspicua after 15 h exposure to freshwater at 8°C. At higher temperatures the survival is lower. There is a difference in the requirements on water circulation, with R. parva and R. lilacina preferring more current-swept and exposed environments.

Rissoa membranacea occurs in two types, possibly species, with planktotrophic and lecithotrophic larval development respectively. In Scandinavia, populations with lecithotrophic development have a restricted occurrence between Sjaelland and Jylland in Denmark, but may be more common in the UK and France. Such specimens are always accompanied by the planktotrophic form, and it can not be excluded that the two forms are conspecific and this is a case of poecilogony. There is also a possibility that P. sarsi actually constitutes a series of populations of P. inconspicua adapted to local, more brackish conditions by larger egg size and veligers, but the two are regarded as distinct species.

The morphology of the spines of the ophiuroid Ophiocomina nigra is described, with particular reference to the nervous system and the sensory and secretory structures of the epidermis. The nervous system is composed of two main spinal nerves, located at the centre of the spine, and their associated branches. There are three secretory cell-types described: (1) fibrillar secretory cells which produce long, javelin-shaped secretory pack-ages and, occurring exclusively in the basal two thirds of the spine, penetrate deeply with their basal regions lying close to the axial nerve running through the spine centre; (2) granular secretory cells, which also penetrate deep within the spine, contain secretory granules in the form of spherical dense vesicles (~1.3 μm in diameter); and (3) goblet secretory cells, filled with packages of loose amorphous material, are superficial in location and usually found associated with a type A ciliated sensory cell. The secretions of the fibrillar and granular secretory cells are thought to perform the functions of defence and feeding respectively. A number of different ciliated sensory cell-types have been identified. Apart from the situation with the goblet cells, no close association was found between secretory and sensory cells. It is suggested that the nervous, sensory and secretory cells act together to form a mucous secretion system with centralized, rather than local control. This system appears to operate when it is advantageous to produce secretion all over the body simultaneously once any portion is stimulated. Stimulation of sensory cells might result in axonal excitation of the spinal nerves and hence to the entire epineural nervous system.

Six mangrove forests in the urban region of Sydney, Australia, were examined to determine whether there were relationships between levels of human-induced damage and the structure of molluscan assemblages, the first stage in the validation of a technique for rapid assessment of the impacts of anthropogenic disturbance in urban mangroves. All six mangrove forests showed some damage but the amount varied considerably among and within each forest. Significant correlations between the levels of damage and abundance of different taxa, and changes in the structure of the molluscan assemblage along gradients of damage, suggest that indices based on measures of damage have the potential to provide a means for the rapid, wide scale evaluation of mangroves affected by impacts associated with human activities in urban areas.

Mytilus edulis (Mollusca: Bivalvia) collected as spat from the wild in 1990 and held in the laboratory for 18 months were divided into four groups: fed (control); starved; fed with 100 ppb added copper; and starved with 100 ppb added copper. Following >60% mortalities in the starved and copper stressed groups (but negligible mortalities in the control) surviving mussels from all four groups were genotyped at seven allozyme loci (Gpi, Lap, Pgtn, Idh, Odh, Gsr and Est). Allele frequencies did not vary significantly between any of the four groups at any loci, except Gsr where fed and starved groups differed. Mortalities were not genotype dependent at the Pgm locus but, in contrast, genotype frequencies at most other loci varied significantly between groups. At the Gpi, Lap, Gsr and Odh loci there were significant changes in proportions of heterozygotes following copper induced mortalities such that, in general, heterozygotes survived longer and homozygotes succumbed sooner. No similar pattern was evident in relation to mortalities caused by starvation; at only one locus (Idh) was there evidence of a significant effect but this was not apparently independent of the effect of copper.

Determination of fossil echinoid diversities is an important aspect of detailed palaeon- tological studies. The comparison of recent and fossil associations can be used to elucidate the problems of determination of fossil echinoid distributions. Actuopalaeontological studies of echinoids from the Red Sea (northern Bay of Safaga, Egypt) have shown that the study of fragments within bulk sediment samples greatly increased the possibilities for determining echinoid presence and distribution. The results show the restricted distribution as well as the differential preservation potential of the various echinoids.

The distribution of echinoids is primarily controlled by grain size, food availability, exposure to current activity, and predation pressure. Regular and irregular sea-urchins show the expected disjunct distributions with the former showing a more undifferentiated distribution to various hard substrates. Irregular echinoids are tightly restricted to particular types of soft substrates reflecting their adaptation to the specific grain size of the sediments. Co-occurring irregular sea-urchins show a spatial differentiation into shallow (clypeasteroids) and deeper burrowers (spatangoids). This investigation shows that important echinoid species known to occur in the Red Sea are lacking or are very rare within the study area, although a large number of different facies types are present. Patchy distributions are present for both regular and irregular sea-urchins. The determination of biodiversity is therefore seen to be largely dependent on the scale of investigation.

An important implication for fossil echinoid presence are the differential effects of taphonomic agents on the various test architectures. Some species are well represented due to their common occurrences, and their comparatively robust tests or test fragments.

INTRODUCTION

Approximately 145 species of the phylum Echiura have been described to the present date (Popkov, 1992). Since Stephen & Edmonds' (1972) monograph detailing the known species of Echiura, few new species have been described. The majority of these have been members of the family Bonelliidae from the deep-sea (i.e. Murina, 1976, 1978; DattaGupta, 1977,1981; Biseswar, 1992) with a few exceptions (e.g. Thalassema malakhovi in Popkov, 1992 and Ochetostoma natalense in Biseswar, 1988).

The rates of gastric evacuation and return of appetite in adult Scyliorhinus canicula at 15°C were quantitatively assessed by serial x-radiographs of fish fed a moist diet containing radio-opaque glass beads, and by re-feeding trials. The evacuation of food from the cardiac stomach of dogfish was exponential in nature. Dogfish were fed small (~26 g of squid diet per fish) and large (~55g of squid diet per fish) meals and greater relative instantaneous rates of emptying occurred after consumption of small meals (k=0–0215) than larger meals (k=0·0086), indicating that the pattern of emptying was dependent on the degree of stomach fullness. There was inverse proportionality between rates of gastric evacuation (GE) and return of appetite (RA) after consumption of similar sized meals, with instantaneous rate coefficients being similar in magnitude (GE, k=0·0086; RA, k=0·0063). These results suggest that the rate of gastric evacuation is closely correlated with the return of appetite in S. canicula. An hypothesis is forwarded describing the possible physiological role of gastric evacuation rate in appetite regulation.

Major hotspots of amphipod species richness and of species and generic endemicity can be recognized in shallow seas. Recognition of ‘hotspots’ for amphipods must take account of the species-area relationship but not of latitude. The richness and endemicity of amphipods in the Mediterranean Sea is shown to be high when compared with other shallow seas This indicates a long in situ evolutionary history and is therefore not compatible with the hypothesis that the Mediterranean fauna was extirpated in the late Miocene.

The mussel Mytilus edulis (Mollusca: Bivalvia) feeds on suspended matter filtered from the sea-water by cilia on the gill surfaces. The bivalve will clear the inhalant water of all particles >2–3 (xm including both sediment and organic matter. Marine sediments act as sinks for a variety of pollutants which may be concentrated up to 1000 fold above water levels. In a series of experiments, the uptake of zinc by M. edulis from filtered sea-water was compared with that from sea-water containing particulate matter acting as model sediments. The materials were two different ion-exchange resins, inorganic granules and hydroxyapatite particles. The accumulation of zinc from the particles was related to the amount of zinc adsorbed by the particles and to their surface properties.

The taxonomic relationship between the limpets Patella rustica (Mollusca: Archaeogastropoda) and P. piperata is unclear with controversy as to whether P. piperata should be given specific status. The problems stem from its similar morphology but different biogeographic range from P. rustica. Individuals from seven populations of P. rustica and three of P. piperata were analysed for a combination of morphological and genetical characters. Morphological analyses of shell shape and radular morphology revealed differences between species for radular length, higher in P. rustica than in P. piperata, and the shape of the pluricuspid teeth of the radula with a well-developed internal cusp in P. piperata but not in P. rustica. Electrophoretic results based on 11 allozyme loci, however, did not distinguish the two species clearly. The overall genetic identity value between the two was 0·861, a value which lies within the range for conspecific populations of other patellids. It is proposed that P. piperata on the basis of the genetic data obtained, may represent a subspecies of P. rustica that is in the process of diverging due to its geographic isolation.