Oceanic and coastal bioluminescence in surface waters, in many instances, is produced by microscopic dinoflagellates. Their light emission is usually observed at a maximum during the night hours and markedly inhibited during the day. This diel periodicity has never been observed in situ for identified species and never before in heterotrophic Protoperidinium dinoflagellates. Pronounced differences in stimulable bioluminescence measured with bathyphotometers in Vestfjord, Norway in September 1990 correlated with simultaneous ship-board laboratory experiments. Cells of both the photosynthetic Ceratium fusus and heterotrophic Protoperidinium curtipes showed a pronounced inhibition of bioluminescence during the day and maximum bioluminescence at night.

The aspidochirote Holothuria forskali is a large common species found in the Atlantic and the Mediterranean. Its reproductive cycle has been determined in a population from Brittany using histological observations of the different classes of gonadal tubules, oocyte size frequencies and evolution of gonad indices. The cycle is annual and synchronous in both sexes. The different phases are well marked and are characterized by a long maturation during summer and autumn followed by a pre-spawning period during winter. Spawning is probably related to the increase in temperature. Most of the mature gametes are released. The resorption of the relict and spent tubules continues during the onset of the next vitellogenesis in the secondary tubules, without a rest period. The reproductive effort, documented from the gonad indices, is very high in this population which is composed of adult individuals.

Comparative ultrastructural features of the ovary and vitellogenesis have been described for six shallow water and four bathyal species of sea cucumbers representing four major holothuroid orders. Ovarian structure is similar in all ten species except for features of the peritoneal cells of the outer layer and the follicular inner epithelial cells surrounding the developing oocytes. The peritoneal cells vary from monociliated squamous or cuboidal cells to large columnar cells. Ultrastructural evidence suggests that these cells might be capable of incorporating materials from the perivisceral coelom. The follicular inner epithelial cells of two deep-sea species resemble podocytes, a feature previously unre-ported in holothuroid ovaries. It is suggested that these cells function to increase nutrient exchange between the genital haemal sinus and the oocyte during vitellogenesis. In all ten species, the oocytes appear to participate in yolk synthesis through the interaction of the Golgi complex and rough endoplasmic reticulum. The similarity in the ultrastructural features of vitellogenesis suggests that the process of yolk synthesis has been highly conserved in holothuroids. Endocytotic activity was detected in seven of ten species but it is uncertain if this is directly related to vitellogenesis. Cilia and intracellular structures resembling striated ciliary rootlets were observed in the oocytes of four of the ten species studied. The significance of this finding is unclear but could indicate that germ cells have a somatic cell origin.

The development of the lecithotrophic encapsulated larva of the internally-fertilizing, sublittoral gastropod Turritella communis Risso 1826 was documented using scanning electron microscopy and light microscopy. Encapsulated development was completed in 12 days at 15°C in the laboratory. Spawning occurred above ~10°C. Spawn masses consisted of numerous gelatinous egg capsules, each of which contained ~28 eggs, encased in albumen and fertilizing sperm. The eggs had an average diameter of 139 μm. Fertilization was accomplished by unpaired eupyrene sperm and occurred at the germinal vesicle stage. The developmental sequence followed the typical gastropod pattern, but was unique in a number of respects. Polar lobes were produced during meiotic maturation and early cleavage, with an especially large lobe occurring in association with the first cleavage, which was unequal. The blastula developed into a dorso-ventrally flattened placula at the 70-cell stage. Gastrulation occurred through invagination and epiboly acting together, and was uniquely accompanied by the development of ectodermal microvilli measuring ~ 1 μm in length. Extra-embryonic albumen began to be depleted after the development of the microvilli. It is proposed that the ciliated telotrochal cells gave rise to the pair of statocysts. Torsion was additionally observed to be facilitated by the growth of pre-mantle tissue on the right side and retardation of growth on the left side.

The biology of young scallops Pecten maximus (Mollusca: Bivalvia) was examined using SCUBA diving. Within shallow and sheltered bays settlement took place near adult populations. Surfaces to which scallops attached were generally free of silt; these included algae, invertebrate tests and inorganic materials. Detachment could take place amongst individuals of 1 mm; however, in sheltered bays most remained attached until 4–13 mm. Following detachment scallops recessed in sediment. They were subject to dispersal by water turbulence and swimming induced by sea-stars. There was evidence to suggest high mortality from crab and sea-star predation during the summer and autumn.

The distribution of larvae of sprat (Sprattus sprattus) is described in relation to feeding conditions in the Irish Sea. Larvae were most abundant towards the coastal margins. Relatively few were taken in the mixed water of the central Irish Sea. Preferred food organisms were also more abundant in coastal regions. Both sprat eggs and larvae, and microplankton, were more dispersed down the water column when it was fully mixed than when stratified. Characterization of food availability for larvae, as peak (modal) abundance down the water-column, is shown to be related to the degree of stratification.

Male diamondback terrapins, Malademys terrapin (190–240 g; 101–117 mm carapace length; 11–8 ±0–6 mm maximum jaw gape) selected small littorinids (<12 mm shell height) and mussels (<30 mm shell length) when offered prey of a range of sizes (at 26°C and 34‰. Jaw gape appeared to be the main constraint on feeding on molluscs. Responses to crabs were complex. Small crabs (10–25 mm carapace width) were eaten whole. Medium-sized crabs (30–50 mm carapace width) were ‘cropped’ (i.e. walking legs were eaten without killing the crabs). Large crabs (52–75 mm carapace width) were usually avoided, though terrapins sometimes took legs from pairs 3 or 4. Experiments with medium-sized crabs showed that diamondbacks evaluated crabs visually before attacking and preferred to eat crabs without chelipeds, rather than crabs with one or two chelipeds. Terrapins carried out attacks on medium-sized crabs from the side or rear and preferentially cropped leg pair 4 (the furthest from the chelipeds), even though leg pair 4 was significantly less valuable energetically than other leg pairs. Evidence is presented to show that cropping behaviour allows terrapins to exploit crabs which are too large to eat whole because of the constraints of jaw gape and the hard, smooth surface of the crab cephalothorax. Limb cropping is as energetically profitable as eating small crabs whole, but the threat posed by chelipeds causes terrapins to attack crab prey in the order small>medium>large.

The stomach contents of 235 specimens of the squid Sthenoteuthis oualaniensis (4·3–36·5 cm mantle length, ML) were examined. A detailed list of 60 species of prey, comprising young and adult squid, is given together with their frequency of occurrence and proportional contribution. The size and number of each food item was investigated. Three ontogenetic size-groups of S. oualaniensis were distinguished: I, fry and young (4–10 cm ML), micronektonic epipelagic plankton-eaters; II, transient critical size group (10–15 cm ML), converting from feeding on planktonic crustaceans and fish larvae to myctophid fishes; III, medium-sized (adult) nyctoepipelagic nektonic predators (15–36·5 cm ML), feeding primarily on myctophids and secondarily on squid. Myctophids (genera Symbolophorus, Myctophum and Hygophum) were the most abundant prey in the diet of adult S. oualaniensis from different parts of its distribution.

Cephalopod remains from the stomachs of a Risso's dolphin (Grampus griseus Cuvier, 1812, Cetacea) entangled in a fishing net off the Ligurian coast (central Mediterranean Sea) include squids Ancistroteuthis lichtensteini, Histioteuthis bonnellii, H. reversa and Todarodes sagittatus and the sepiolid Heteroteuthis dispar. All these cephalopods live in oceanic water including water over the steep continental slope where Risso's dolphin is frequently sighted. Histioteuthis reversa contributed 78% of the cephalopods by number, 81% of the wet weight and 73% of the dry weight and calorific value. The total calorific value of the cephalopods represented by lower beaks was 17,300 kj.

The distribution of Neomysis integer (Crustacea: Mysidacea) in a tidally mixed estuary was found to be concentrated in mid-estuary with animals extending, primarily in summer, further up and down estuary. Within this range there were distinct intra-specific differences in distribution, with males occurring more commonly down-estuary and ovigerous females and juveniles up-estuary. Examination of tidal abundances in mid-channel showed males to be more abundant on the ebb tide, corresponding with their more downstream distribution, and all other individuals to be present mainly on flood tides, which would maintain the species within the estuary. Endogenous circa-tidal swimming activity in this species was found to be phased after the time of expected high tide, which would suggest ebb tide swimming in the estuary. More detailed examination of the distribution of Neomysis across the width of the estuary showed greatest concentrations of animals in slow-flowing water at the edge of the channel during the ebb tide. The endogenous swimming rhythm may therefore act to prevent stranding of animals intertidally during the ebb tide, while maintenance of position along the estuary appears to be by flood tide swimming under exogenous control.

When observed from a submersible, the mesopelagic paralepidid Notolepis rissoi (Pisces: Paralepididae) will hover head up with the body at about 45°. The fish's swimming motion is restricted to the extreme caudal region with most of the body rigid. The trunk lateral-line canal ends at about the position that caudal motion becomes noticeable and there is a great decrease in neuromast size near the posterior end of the canal. The size of the neuromasts is also inversely related to the percentage of red muscle at the same body level. The eyes have an aphakic space oriented dorso-anteriorly at about 45° to the body axis so that during hovering the aphakic space is oriented vertically. Retinal anatomy indicates that photoreceptors opposite the aphakic space appear to enhance resolution at the cost of sensitivity, whilst lateral photoreceptors enhance sensitivity at the expense of resolution. We interpret the swimming attitude and mechanics as adaptations to minimize self-induced oscillations which would be deleterious to visual and lateral-line function.

Samples of branched and unbranched forms of the marine thecate hydroid Aglaophenia pluma (L.) (Hydrozoa, Plumulariidae) were collected from the western and eastern sides respectively of Carmarthen Bay (South Wales). Tissue from various colonies of each type was cleaned of epifauna and homogenized for horizontal starch gel electrophoresis. Useful results were obtained for 14 enzyme loci coding for a total of 11 different enzymes. Eleven of the 14 loci showed no common allele between the branched and unbranched forms. Nei's genetic identity was estimated as 0·18 and genetic distance as 1·7. Such a high level of genetic differentiation between morphotypes provides strong evidence that the populations are reproductively isolated and should be regarded as distinct species. It is suggested that the branched form may be Aglaophenia parvula Bale, a species until recently better known from the southern hemisphere. Morphological distinctions between the two species are discussed.

The status of the prayine siphonophore genus Prayoides, monotypic for the species Prayoides intermedia Leloup, 1934, is reviewed in the light of recent collections made by the submersibles ‘Johnson-Sea-Link’ I and II. It is concluded that the genus is not valid, and that the species name should be reduced to that of a junior synonym of a Praya species. The bracts of the two Praya species, P. dubia (Quoy & Gaimard (1833) 1834) and P. reticulata (Bigelow, 1911) are re-described, as in the past there has been much confusion as to their true identity.

A new species, Oikopleura villafrancae, from the family Oikopleuridae (Lohmann 1915), subfamily Oikopleurinae (Lohmann 1896), genus Oikopleura (Mertens 1830), is described from numerous specimens collected at mesopelagic depth (360–880 m) during two different cruises: Migragel II (May 1988) and Medapp (May 1990) in the Ligurian Sea (northwest Mediterranean) between Villefranche-sur-Mer (French Riviera) and Corsica, respectively by the ‘Cyana’ and ‘Johnson-Sea-Link’ manned submersibles.

Relationships between size, wet weight, dry weight, carbon and nitrogen content were determined in Ophiothrix fragilis (Echinodermata: Ophiuroidea). Such relationships appeared very useful when studying dynamic processes such as nutrition, growth, excretion or reproduction, considered as fluxes of carbon and nitrogen in the ecosystem.

Relationships between size, wet weight, dry weight, ash free dry weight, carbon and nitrogen content of organisms are of fundamental interest in ecological studies of ecosystems. They allow us to understand and quantify the role of a species as it stores, consumes or produces organic matter during its life cycle. Determination of conversion factors are time-consuming but very useful for estimating flows in the ecosystem (Brey et al., 1988). Some compilations of conversion factors have been published (Båmstedt, 1981; Rumohr et al., 1987).

Ophiothrix fragilis (Abildgaard) is the dominant species of the ‘pebbles with sessile epifaunal community’ (Davoult, 1990), located in the Dover Strait (eastern Channel), where tidal currents are very strong. It is considered as an efficient suspension feeder (Roushdy & Hansen, 1960; Warner, 1971) and lives in dense populations (1000–2000 individuals m-2; Davoult, 1989) which are assumed to have a significant effect on the fluxes of organic matter from the pelagic to the benthic system and on the fluxes of ammonium to the water column (Davoult et al., 1991).

Individuals were sampled in May and June 1991 off the Cape Gris-Nez (50°55′N 1°35′E). Two-hundred individuals were measured (diameter ±01 mm, after Guille, 1964), dried at 60°C for 48 h, weighed (±0·1 mg), burnt at 520°C for 6 h (Anonymous, 1986), and the ash weighed (±0·1 mg). Total organic carbon and nitrogen content were determined with a CHN element analyser (Carlo Erba 1106): after a flash combustion in a helium stream temporarily enriched with pure oxygen, quantitative combustion was achieved by passing gases over Cr2O3 after a transfer through a reduction reactor to eliminate the excess of oxygen; components were separated in a chromato-graphic column, eluted, then measured by a thermal conductivity detector. Thirty-eight dried ophiuroids were ground with a micro-grinder, then two sub-samples (except for individuals <2 mm) were weighed at ±1 μg (76 measurements).

An earlier time-series of the annual mean latitude of the north wall of the Gulf Stream is updated to give a series of values from 1966 to 1990. The trend is similar to those seen in plankton from the Continuous Plankton Recorder Survey around the British Isles. This connection may reflect the displacement of storm tracks across the North Atlantic.