Submarine caves with sulphurous springs at Cape Palinuro, Campania, Italy, have a richer fauna than expected from the known oligotrophic nature of the cave habitat. Warm water containing sulphide issues from springs and rises above the cooler ambient sea-water with a sharp thermocline/chemocline between. The warm water then escapes from the caves mixed with cooler sea-water, probably inducing an inflow of ambient sea-water. Bacterial mats, often dominated by large species of attached bacteria resembling Beggiatoa, line the upper parts of the inner caves and act as primary producers, fixing CO2 by means of the autotrophic enzyme ribulosebisphosphate carboxylase. Many of the animals in the innermost parts of the caves live close to the chemocline or just below, where they would experience fall-out of bacterial organic matter, and some carry filamentous bacteria on their tubes and hard parts. Dominant members of the community include sponges, cnidarians, and tubicolous polychaetes.

Microzooplankton from water samples collected from depths of between 10 and 50 m at four stations between 47° and 60°N along the 20°W line of longitude during each of three cruises were classified into taxonomic groups and measured to estimate their abundance and biomass. Metazoan members of the microzooplankton were rarely found and their overall biomass was negligible in comparison with protists. The mean numbers of protistan microzooplankton cells >15 μn ranged between 3 and 11 cells ml-1, with mean biomass values between 2 and 14 μgC 1-1. Numbers and biomass increased towards midsummer and then decreased again, except at the most northerly station where the values were highest in the early August sample. The ratio of dinoflagellate to ciliate biomass tended to increase through the summer to levels of three or four and then decrease again, with later changes further north; this ratio also tended to be higher at deeper levels than in the mixed layer. Gymnodinioid forms usually dominated dinoflagellate numbers and biomass, but they were overshadowed by Protoperidinium and others at the two southern stations in June and July samples. Strombidium species were the dominant ciliates, commonly providing 25–50% of total microzooplankton biomass, while predatory haptorid ciliates were occasionally numerous, but tintinnids never formed more than 10% of the biomass.

Metazoan meiofauna were studied in replicated multiple-corer samples obtained at a bathyal site (1320–1360 m depth) in the Porcupine Seabight (51°36′N 13°00′W) before (April) and after (July) the delivery to the seafloor of a phytodetrital pulse originating from the 1982 spring bloom. In all samples the metazoan meiofauna was dominated by nematodes; harpacticoid copepods and their nauplii were the second most abundant taxon. Population densities and biomass were very similar in both sample sets, the only significant differences being in the numbers of ostracods (higher in April) and nauplii (higher in July). Furthermore, vertical distribution patterns in the top 5 cm of sediment indicate that the meiofauna did not migrate towards the sediment surface following the phytodetrital pulse. The lack of a metazoan meiofaunal response contrasts with published evidence, based on the same samples, for a substantial increase in the foraminiferal abundance following the sedimentation event. Thus our results suggest that metazoans (as a whole) fail to exploit and utilize phytodetritus as rapidly as foraminifera. This probably reflects the energetic expense of egg production coupled with frequently slower rates of somatic growth among metazoans. In addition, foraminifera may outcompete metazoans for detrital food because they possess extremely efficient food-gathering organelles (granuloreticulate pseudopodia) and are able to raise their levels of metabolic activity very rapidly. However, metazoan responses at the species level, or over longer time periods (>3 months), would not have been detected and so remain a possibility.

The sublittoral off central Chile represents a dynamic border separating an oxic surface equatorward current and an oxygen-poor poleward undercurrent. This investigation dealt with whether megafaunal assemblage structure and its temporal and bathymetric distribution were affected by this feature. The problem was approached by investigating the empirical relations between an assemblage index of abundance and physical factors of the environment. The megafauna off Conceptión Bay, central Chile (36°32′S) was thus sampled with an Agassiz trawl on eight cruises performed during 1991 and 1992 at three fixed stations (40, 64 and 96 m depth). Simultaneous reference samples of sea-water were taken to measure temperature, salinity, and dissolved oxygen. Descriptive assemblage attributes, diversity indices, and principal component analysis (PCA) for assemblage study were used. Moreover stepwise linear regression, with the first principal component of the specific abundance matrix as dependent variable was used to study relationships between temperature, salinity and dissolved oxygen and an assemblage of 23 species. Species richness, biomass and abundance decreased significantly with depth while diversity was highest in the intermediate depth station. Discontinuities were thus evident between the shallow, intermediate and deep stations. The grouping of samples in the plane formed by the first and second principal components showed a similar bathymetric discontinuity. In the Euclidian plane, a seasonal cycle of variation of the shallow sampling site was evident. Between 46 and 64 m depth lies a boundary separating different states of the same assemblage, the shallow seasonally variable and the deep constant. The intermediate station shares characteristics of both these stations reflecting a more variable environment. The overall bathymetric and the shallow seasonal patterns of variation were statistically linked to dissolved oxygen.

The size distribution of benthic nematodes was investigated along different gradients of food availability in various regions of the north-eastern Atlantic: I, across the continental margin and II, with increasing distance from the continental rise. An overall trend for miniaturization with increasing distance from the food source was found. Moreover, our results indicate that seasonally varying food supply or a periodically pulsed input of organic matter to the sea floor affects nematode size spectra. The hypothesis is proposed that the life cycle of deep-sea nematode species and hence the size structure of their populations are related to seasonal energy availability. This dependence might result in one year life spans of deep-sea nematodes and probably other meiofauna.

Scavenging amphipods were studied at three locations along the 20°W meridian in the north-eastern Atlantic using vertical arrays of baited traps. The sampling sites had several features in common. All amphipods captured belonged to the superfamily Lysianassoidea. Generally, highest densities of amphipods were found in the bottom traps. Abundances as well as species diversity were strongly reduced in traps exposed from 8–500 m above bottom. However, differences between stations occurred in standing stocks, decreasing from north to south, in the taxonomic composition of the bait-attending amphipods and in the vertical distribution and size structure of the giant amphipod Eurythenes giyllus.. Possible reasons for the differences between the locations are discussed and the establishment of at least two provinces in terms of bait-attending amphipods in the eastern North Atlantic is suggested.

A technique is described for the in vitro culture of the eggs and embryos of amphipod crustaceans. The technique was used, with mixed success, to culture the eggs of four species of amphipod (Gammarus duebeni, Orchestia gammarellus, Gammarus pulex and Echinogammarus pirloti) through to hatching. Eggs of the brackish water G. duebeni showed good hatching success in culture (70–75%) over a wide range of experimental salinities (75–1250 mOsm kg1). The eggs of O. gammarellus showed higher mortality rates in culture (compared with G. duebeni), especially in more dilute salinities (300 mOsm kg1) in which they swelled greatly prior to disintegration. Survival and true growth (as distinct from osmotic swelling) of O. gammarellus embryos in dilute salinities were significantly im-proved by introducing embryos into culture at a later stage of development. Antibiotic treatment had no demonstrable effect on embryo survival or growth. Whilst difficult to culture using this method, the eggs of the fresh water G. pulex showed best hatching success on a very dilute saline medium (~40 mOsm kg1). The results are discussed in relation to the development of embryonic osmoregulation, the implications for brood pouch function and the potential for female control of the embryonic environment, especially in semi-terrestrial species.

Adult individuals of Talitrus saltator were tested for celestial orientation in a plexiglass bowl covered with colour filters of different wavelengths. Results show that T. saltator can recognize the sun and use it for orientation only at γ <450 nm. At γ >500 nm, the sight of the sun (and sky) only induces phototactic behaviour. It has also been confirmed that an important celestial orienting factor is perceived in the UV range. Variations in populations from diversely oriented coastlines are discussed. Preliminary results of electroretino-graphic responses indicate the presence of at least two visual pigments in the eye and a steep decrease in sensitivity for γ >500 nm.

Angular sensitivity functions were determined electrophysiologically for retinula cells in Nephrops norvegicus and Munida rugosa. For such aquatic species it is shown that reliable measurements cannot be obtained unless the eyes are submerged. In both cases, for submerged eyes, there is a significant reduction in retinula cell acceptance angles with light adaptation. In N. norvegicus the change is from 11·3° dark adapted (DA) to 8·85° light adapted (LA). In M. rugosa there is a larger difference, 12·5° (DA)–6·58° (LA). The changes in acceptance angle with adaptational state can be attributed to differences in screening pigment position between light- and dark-adapted eyes. In N. norvegicus only the retinula cell proximal pigment is migratory. The small change in acceptance angle with adaptation is consistent with the fact that the eye uses superposition optics even when light-adapted.

Based on the bivalve fauna known from an extensively studied zone, along the infralittoral in the Patras Gulf, a biotope approach was attempted using numerical taxonomy methods. The efficiency of various combinations of similarity measures and clustering techniques is discussed for this type of data (single group – binary). Four main station groups were delimited which were further assigned to the biotopes of known Mediterranean biocoenoses. The four groups correspond to: (a) the biotope of the Posidonia beds (HP) and that of coarse sands and fine gravels under the influence of bottom currents (SGCF). The limits of these two biocoenoses are not clear-cut, (b) The biotope of the coastal detritic bottoms (DC) usually occurring in deeper areas but met in the infralittoral under environmental stress, (c) A transitional zone where degenerating Posidonia meadows are gradually replaced by Cymodocea and Zostera, facies of the muddy sand in sheltered areas biocoenoses (SVMC). This degradation can be attributed to various disturbing factors including natural environmental changes, (d) The biotope of fine well-sorted sands (SFBC). A typical malacofauna is present with the addition of some species. Regardless of the differences, Pérès & Picard's (1964) scheme is more appropriate in the Mediterranean ecosystems than any other northern European scheme.

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.

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.

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.

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.

INTRODUCTION

The deep-sea eel, Synaphobranchus kaupi, is widely distributed on the continental slopes of the North Atlantic (Saldanha & Bauchot, 1986; Haedrich & Merrett, 1988). It was a dominant fish species in epibenthic sledge and semi-balloon otter trawl (OTSB) hauls on the West African slope (Merrett & Marshall, 1981; Merrett & Domanski, 1985). Also in the eastern North Atlantic, it was the most abundant species on the slopes of the Porcupine Sea Bight off south-west Ireland (Merrett et al., 1991; Priede et al., 1994). In the western North Atlantic, it was the dominant species on the middle and lower slopes of the Middle Atlantic States of the USA and on the upper slopes of the Grand Banks off Newfoundland (Sedberry & Musick, 1978; Houston & Haedrich, 1986).

The aims of the present study were to investigate food consumption, growth and the dynamics of feeding hierarchies in the same groups of juvenile greenback flounder (Rhombosolea tapirina: Teleostei) fed either high or low rations. Differential food consumption by individual greenback flounder held in groups of 20 showed the presence of feeding hierarchies in which individuals consumed between 0 and 22% of the available food. Inter-individual differences in food consumption resulted in different growth rates leading to growth depensation (measured as an increase in the coefficient of variation for weight). Intra-individual differences in food consumption tended to be larger for flounder which consumed a lower share of the available food. When the group ration was reduced the inter-individual and intra-individual variations in food consumption increased. Consequently, the relationship between inter-individual and intra-individual variation in food consumption tended to become stronger at lower food availability and indicated an increase in the strength of the feeding hierarchies. This study suggests that individual differences in food consumption, mediated through exploitation competition, contribute to growth depensation in this species of flatfish.

The glandular epithelium of both escae and caruncles originates from a solid, branched ingrowth of epidermal cells from the distal surface of the bulb-shaped light gland primordia in the larva. The lumina within the glandular epithelium appear to originate by the breakdown of the central cells within the solid mass of epithelial cells. An epithelium-lined duct connecting the central glandular lumina with the distal surface of the bulb-shaped primordium was seen only in sections of the posterior esca. This suggests that the intraglandular lumina are formed before the duct to the surface, which then develops within an initially solid strand of cells.

In this paper we present evidence for female mimicry in a population of Salaria pavo (Pisces: Blenniidae). Parental males differ markedly from females by the presence of a large crest on the head and anal glands on the two spiny rays of the anal fin. We found a proportion of smaller and younger males that are almost identical to females both in morphology and behaviour. These ‘female-like’ males lack secondary sexual characters and actively court parental males, displaying the female's colour pattern and courting behaviour. These males are sexually mature and their gonadosomatic indices are higher than those of parental males. Female mimicry is considered to be a functional way to achieve sneak fertilizations.

Penis size and morphology of an oviparous species of rough winkle Littorina arcana Hannaford Ellis (Gastropoda: Prosobranchia) was studied at Robin Hoods Bay on the English east coast. Monthly collections were made over a two year period from August 1987 to August 1989 and again from May to December 1993. Number of penial glands was recorded and a six point scale was used to quantify penis maturity. Results indicate that male L. arcana shed their penes in summer and regenerate a new one during the following 12–20 weeks. Male L. arcana in captivity shed penes in July but not in November. The significance of penis shedding and the differences in reproductive seasonality between L. arcana and its ovoviviparous sibling species L. saxatilis is discussed.