Geographic variation of allele frequencies at four loci in Chlamys opercularis was investigated using electrophoresis on polyacrylamide gels. Large differences were observed between populations at a protein locus, while some small but significant variations occurred at the phosphoglucomutase-2 and octopine dehydrogenase loci. The leucine aminopeptidase locus appeared monomorphic. On the basis of mean genetic identities derived from three loci in nine populations and hydrographic data on coastal current systems, it is proposed that there are at least four relatively genetically isolated populations of this scallop around the British Isles, namely (1) North and West Scottish coast, (2) the Irish Sea, (3) the Celtic Sea (Brittany coast) and (4) the English Channel. It is argued that both random genetic drift and selection may play a significant part in the establishment and retention of large allele frequency differences between isolated populations of this species.

Mature eggs were stripped from ripe adult specimens of Arctica islandica and exposed to a dilute solution of ammonium hydroxide for various lengths of time before addition of stripped sperm. Larval and early post-larval stages were cultured under experimental laboratory conditions using standard bivalve rearing techniques. Larval cultures were maintained at various controlled temperatures ranging from 8·5 to 14·5 °C. Minimum time to settlement was 32 days at a temperature of approximately 13 °C; at temperatures between 8·5 and 10·0 °C, settlement was not observed until approximately 55 days after fertilization. Larval growth rates were significantly faster at temperatures between 11·0 and 145 °C than at temperatures between 8°C. Morphometry of the larval shell and morphology of the larval hinge apparatus were independent of larval growth rates and experimental culture conditions.

Dunal (1837) originally described the taxon now known as Dunaliella salina (Dunal) Teodoresco, 1905, as consisting of spherical or elliptical cells, red-orange to rust coloured. Teodoresco, in his definition of the species (1905) stated that the zoospores had a green chromatophore but in aged zoospores the entire body, including chromatophore, was red. Thus, by definition, any isolate of Dunaliella which is not capable of turning redorange to rust coloured should not be considered D. salina. Several strains have been reported in the literature under the name D. salina but do not meet the aforementioned criteria. These include UTEX 200 (= Cambridge 19/3), Mil'ko's strain (Mil'ko, 1963 a, b) and Strain No. 6 used by Mironyuk (Drokova, 1970; Drokova, Popova & Tupik, 1964; Drokova & Popova, 1973, 1974; Mironyuk 1969a, b; Mironyuk & Einor, 1968).

INTRODUCTION

The family Palmariaceae Guiry (Palmariales: Rhodophyta) at present includes the genera Palmaria Stackhouse (the holotype genus: see Guiry, 1974, p. 523), Halosacdon Kiitzing, Leptosarca A. & E. S. Gepp and Neohalosacdocolax I. K. Lee & Kurogi. Halosacdon and Leptosarca were included in the original description of the family (Guiry, 1974) and Neohalosacdocolax was recently described by Lee & Kurogi (1978) for a small parasite on Halosacdon minjaii I. K. Lee from the Aleutian Islands. The structure and reproduction of Neohalosacdocolax make it quite clear that its affinities lie with the Palmariaceae (Lee & Kurogi, 1978). The Palmariaceae of the island of Hokkaido (northern Japan) have been the subject of a recent study (Lee, 1978) and the details of structure and reproduction given for the northwestern Pacific species of Palmaria and Halosacdon confirm that the unusual structure and mode of reproduction described by Guiry (1974, 1975, 1978) for Atlantic and northeastern Pacific representatives of these genera are also found in the northwestern Pacific representatives (see also Lee, 1977a).

Determining the duration and timing of spermatogenesis in Mytilus californianus Conrad became key questions in our study of carcinogen-mutagen indices in the marine environment. We had postulated that the murine sperm deformation assay of Bruce, Furrer & Wyrobek (1974) should have marine analogues, and we assayed a number of marine invertebrates sampled near potentially carcinogenic waste flows, and by γ-ray dose-response experiments. Our field results demonstrated some deformation but only at a very low level (less than 5 % in Mytilus edulis L.). Development of a γ-ray doseresponse (90–900 rads) procedure for M. californianus by radium needle inserted through a drilled hole closed with a plastic plug, and subsequent biopsy of gonadal tissue at measured distances from the site of irradiation, did not show deformations from a pilot test in June 1979. If a viable dose-response procedure was to be developed it was necessary to establish seasonal reproductive timing so that specimens could be collected or cultured to maximize spermatogenesis and hence response potential, and also to establish the duration of spermatogenesis so that response measures via a gonadal tissue extraction could be appropriately timed.

Red tides of the naked dinoflagellate Gyrodinium aureolum Hulburt occurred in sealochs in the north of the Firth of Clyde, Scotland, during late September 1980. Greatestconcentrations of the organism were found in the top 1 m layer of the water column, which was stabilized, and probably also enriched with nutrients, by freshwater input fromland drainage. In addition vertical and horizontal concentration must be postulated toexplain Gyrodinium cell densities of 2 x to7 cells I"1 and chlorophyll concentrations of 2228 mg m“”3 near the shore at Otter Ferry, Loch Fyne.

On 28 September 1980, water containing the red tide at Otter Ferry was unintentionally pumped into fish ponds at a shore-based salmon farm and resulted in the death, in one pond, of 3000 salmon each weighing about 1 kg and of 200–300 smolts in another when water was transferred to it from the affected pond. Pathological investigation of affected salmon showed that death was likely to have resulted from asphyxiation and osmotic shock as a result of extensive cellular damage to gills and guts. Results of mouse bioassays, using acidic and ether extracts of flesh and guts from affected salmon, suggest that necrotizing toxin(s) was associated with the cells of Gyrodinium aureolum during the bloom. The clinical signs exhibited by mice injected with toxin extracts were, however, unlike those caused by paralytic shellfish poison or toxins of the Gymnodinium breve type.

Jet propulsion in the small siphonophores Chelophyes and Abylopsis was investigated by measuring chamber pressures and thrust exerted in tethered nectophores, and by cinephotography of free swimming colonies. Although of similar design, the two siphon-ophores swim at different speeds, and with very different chamber pressures in the locomotor nectophores. Estimates of drag incurred during swimming, and of the cost of the process in the two forms are discussed.

INTRODUCTION

In 1976 the Fisheries Laboratory, Lowestoft, carried out 13 plankton sampling cruises off the north-east coast of England. They spanned the months February-November. From these cruises Harding et al. (1978) described the distributions of surface chlorophyll and nutrients and the production offish eggs and larvae. Reynolds (1978) described in more detail the distributions of chlorophyll and phaeopigments throughout the year, and Horwood (1982) detailed the distribution of zooplankton biomass. This study presents the species composition of the algae from a small region of the survey area illustrated in Fig. 1.

In the Southern Bight of the North Sea, off the Belgian coast, exists a series of parallel sublittoral sandbanks, the Flemish Banks, situated in a southwest-northeastern direction, 15–25 km long and 3–6 km wide. They are separated by channels, 4–6 km wide, and rise about 25 m above the surrounding sea-floor (Fig. 1). These sandbanks resulted from the accumulation of sandy deposits of glacial origin sedimented by the giant stream draining the waters from the present Rhine, Meuse, Scheldt and Thames before the Flandrian marine transgression about 12000 years ago. When from boreal times onwards the North Sea became slowly inundated, a connexion existed with the small English Channel which gradually enlarged, resulting in the very strong tidal currents which are responsible for the present geomorphology of the region.

The population of Streptosyllis websteri at Newton, Northumberland shows epigamous reproduction and has an extended spawning season from April to July, during which there are two main peaks of spawning activity. Most individuals spawn twice in the breeding season at the beginning of their third year of life, although some individuals may contribute to the second spawning peak of the breeding season at the beginning of their second year. Growth rates are remarkably uniform, and year classes are usually clearly distinguishable using setiger number frequency distributions. Observations on growth and mortality suggest that there is competition for resources amongst the new recruitment class over the first few months of life, but that overall survival through the first year is density independent and likely to be determined by external factors. Larval development is largely benthic, and it is unlikely that there is any prolonged truly pelagic larval phase.

INTRODUCTION

Amoebae of the genus Paramoeba Schaudinn, 1896, are among the Gymnamoebia most frequently isolated from marine habitats, and individual species have a wide distribution throughout the world. Unlike many genera of Gymnamoebia, Paramoeba is exclusively marine. The type species, P. eilhardi Schaudinn, 1896, was originally described from a marine aquarium in Berlin with no further information on origin (Schaudinn, 1896); it has been found in the Mediterranean off France (Chatton, 1953; Grell, 1961) and Italy (Grell & Benwitz, 1970) and the Indian Ocean off Madagascar (Grell & Benwitz, 1970). P. schaudinni de Faria, da Cunha & Pinto, 1922, originally described from a sea-water aquarium at Rio de Janeiro, has recently been reported from the Gulf of Mexico (Sawyer, 1980). P. pemaquidensis Page, 1970, has been found on the coasts of Maine, U.S.A. (Page, 1970), Norfolk (Page, 1973), and Essex (Page, unpublished); in open waters off the eastern coast of the U.S.A. (Davis, Caron & Sieburth, 1978); in marine sediments of the western North Atlantic, the Bight of New York, and the Gulf of Mexico (Sawyer, 1980); and in the present study on the shores of North Wales and western Scotland. Paramoeba aestuarina Page, 1970, though not found as often as P. pemaquidensis, is also widely distributed (Page, 1970; Davis et al. 1978; Sawyer, 1980). The first European finding of P. aestuarina is reported in the present paper, but the exact origin of the strain is uncertain. P. perniciosa Sprague, Beckett & Sawyer, 1969, which appears to be an obligate parasite, has thus far been reported only from crustaceans off the eastern coast of the U.S.A. (Sprague, Beckett & Sawyer, 1969; Sawyer, 1976).

The growth of the octopus Eledone cirrhosa has been studied in a population from the North Sea off Aberdeen. Data are presented for the growth of individuals isolated in aquarium conditions; the growth of size classes in thefieldpopulation; and preliminary information on the growth relationships of gonad, somatic, cardiac and brain components of the body.

At 15 °C Eledone cirrhosa is capable of growing from 10 to 1000 g in 270 days. From octopuses which feed readily in captivity, weight specific growth rates of up to about 3–5 % day-1 for animals of 100 g body weight are recorded, falling to a maximum of about 1–5 % day-1 at body sizes above 500 g. Females stop growing when sexually mature, but in the sample captured they were consistently larger than males, a feature which may account for the 7:1 bias towards the incidence of females. On a wet-weight basis, the mean food incorporation into growth is 37 % of the food ingested, which is 49% of the gross weight of crabs killed. Field data for 1978/79 suggest that animals recruited to the population at the beginning of the year grew steadily until December, overwintered without growing, then grew rapidly for several months in the subsequent year before disappearing from the samples. The estimated average age of those animals and by implication, the life span, is 20 months.

During a series of North Sea demersal fish surveys, a headline camera was used to photograph the sea-bed at intervals of 1 min, throughout the duration of 60 min trawls. A successful series of underwater photographs were obtained at 119 stations throughout the North Sea. In addition, the benthos caught at 317 stations was recorded.

A total of ca. 30 species could be identified on the underwater photographs, and of these ten species were sufficiently common or locally abundant for estimates of local population densities to be made. Distributions throughout the North Sea based on specimens trawled and specimens photographed were compared.

Five hundred and twenty-eight specimens of Loligo forbesi Steenstrup, from landings in Horta, Faial, Azores, during the year 1 March 1980 to 28 February 1981, were tudied; 59·3 % were males, 40·7 % females. Of the males 80·2 % were sexually mature, of the females 91·6 %, both sexes showing the highest degree of maturity in spring and he lowest in autumn. The mean dorsal mantle length of the mature males was 56·5 cm, or females 33·5 cm. A weight-length relationship was calculated. he stomachs of 622 specimens were sampled, of which 306 contained food.

The prey omponents were studied qualitatively. The main prey was fish (82·0%), of which 0·5 % were horse mackerel, Trachurus picturatus, this being the most important food rganism. Preliminary results of statolith readings are given.

The background and aims of this study are outlined in the introductory section of the preceding paper (Vanosmael et al. 1982).

INTRODUCTION

Ophiacantha bidentata (Retzius) is a widespread arctic-boreal ophiuroid with a circumpolar distribution in the shallow waters of the Arctic seas and penetrating into the deep sea of the.North Atlantic and North Pacific (Mortensen, 1927, 1933a; D'yakonov, 1954). Early observations of this species were confined to defining zoogeo-graphical and taxonomic criteria including the separation of deep water specimens as the variety fraterna (Farran, 1912; Grieg, 1921; Mortensen, 1933a). Mortensen (1910) and Thorson (1936, pp. 18–26) noted the large eggs (o.8 mm diameter) in specimens from Greenland and Thorson (1936) proposed that this species had ‘big eggs rich in yolk, shed directly into the sea. Much reduced larval stage or direct development’. This evidence is supported by observations of O. bidentata from the White and Barents Seas (Semenova, Mileikovsky & Nesis, 1964; Kaufman, 1974)..

Stage V copepodites of Calarms finmarchicus collected from the Firth of Clyde during April–August 1978 and October 1979–January 1980 moulted to adults in the laboratory. The interval between capture and ecdysis was longer on average and less variable during the months July–November (when overwintering stocks build up in the Firth) than April–June. Overwintering Stage V copepodites moulted earlier in the laboratory than in the sea; this is not associated with differences in environmental factors known to affect developmental rate and may have been induced by stress associated with capture or handling. A similar induction of moulting is not evident in spring and summer generations.

Following primary settlement and metamorphosis in Myiilus edulu (L.), the original larval stem glands (S1 and S2) increase enormously in size in the plantigrade. These glands, packed with mature secretion, discharge into a multi-partitioned posterior ducted system which is transitional in form between that of the larva and the adult. The gross enlargement of the stem glands appears to be an adaptation for frequent and copious production of byssus material during the bysso-pelagic and attachment phases of early post-larval life. This interpretation is supported by the fact that the volume ratio of the stem glands to the foot declines during subsequent growth of the young mussel and that other glands take over the function of byssus stem formation in mature mussels. Enhanced dispersal of post-larvae by bysso-pelagic drifting would account for the widespread and heavy fouling of offshore platforms by the almost exclusively intertidal mussel, particularly where these structures are far distant from coastal stocks.

INTRODUCTION

The reproductive biology of asteroids from a wide variety of ecological niches has been examined (Farmanfarmaian et al. 1958; Cognetti & Delavault, i962;Pearse, 1965; Chia, 1968; Crump, 1971; Jangoux & Vloebergh, 1973; Worley, Franz & Hendler, 1977; Barker, 1979; Shick, Taylor & Lamb, 1981). Most of the species within this class appear to show some degree of seasonal reproductive synchrony with very few species showing aseasonal reproduction (Shick et al. 1981). Although the seasonally reproducing asteroids show a wide variety of reproductive strategies, from planktotrophic larvae to direct development, they all occur in relatively shallow water and are thus subject to the seasonal fluctuations of the physico-chemical environment. Only two shallow-water species, Ctenodiscus crispatus (Shick et al. 1981) and Patiriella exigua (Lawson-Kerr & Anderson, 1978), have aseasonal reproduction in both males and females. However, the deep sea is the only major environment in the world's ocean for which we have no data for the reproductive cycle of asteroids.

In two previous papers (Vanosmael et al. 1982; Willems et al. 1982) the macrofauna and meiofauna of a sublittoral sandbank in the Belgian coastal waters of the North Sea were described. This sandbank, the Kwinte Bank, is one of a series of parallel linear banks, the Flemish Banks, which are 15–25 km long and 3–6 km wide and rise about 25 m above the surrounding sea-floor. They are stressed, high-energy environments, subject to extreme physical disturbance by the very strong tidal currents which run parallel to the long axis of the sandbank and which put the whole upper layer of the sediment in a state of suspension at times.