Killary Harbour is a fjord or sea loch on the west coast of Ireland. With the growth of aquaculture the harbour has become the site of both raft mussel cultivation and more recently, salmon farming. The successful management of these resources requires a detailed knowledge of the harbour's hydrography and ecology. In 1980/1 an extensive survey of the harbour was made. Papers dealing with primary productivity (McMahon & Patching, 1984) zooplankton (Ryan et al. 1986) and the biology of mussels (Rodhouse et al. 1984 a, b, 1985) have already been published. In this paper, we describe the phytoplankton of the harbour and factors which influence distribution and growth.

An increasing interest has been generated in the potential use of oral vaccines in the prevention of diseases of farmed fish (Ellis, 1985; Manning & Tatner, 1985). As part of an investigation of the fate of ingested antigenic material in fish we have in previous studies (Hart, Wrathmell & Harris, 1986 a, b) examined the ontogeny and morphology of GALT in the common dogfish at the light-microscopic level. GALT was shown to occupy three niches throughout the gut: as accumulations of leucocytes in the lamina propria and as individual cells in the lamina propria and epithelium.

The clupeid fishes Clupea harengus and Sprattus sprattus have small cellular tags projecting from the surface of the epidermis of the head and the margins of the scales. The tags are innervated and assumed to be tactile sensory organs. The fine structure has been investigated by scanning and transmission electron microscopy. The protruding part consists of a core of four columns of cells joined by numerous desmosomes, less firmly attached to a single layer of superficial cells. Fine, varicose, nerve fibres run under the superficial cells and end freely. Beneath the tag is a group of prominent basal layer cells and a dermal intrusion with a small nerve. No Merkel cells have been detected in the organs.

A 5-year study of the population biology of the common shrimp Crangon crangon (L.) in the Bristol Channel is reported. Samples were collected from three commercial fishermen and from the filter screens of five power stations taking water from the estuary.

The Severn Estuary and Bristol Channel were found to contain a single shrimp population which undertook regular seasonal migrations in order to avoid low salinities and to reproduce. Previous studies had assumed that the regions held separate populations which migrated to avoid low winter temperatures.

The geographical distributions and seasonal cycles of pelagic larvae and post-larval stages of decapod Crustacea in the north-eastern Atlantic and the North Sea during 1981–3 are described from samples taken with the Continuous Plankton Recorder (CPR). Analyses of the distributions of 36 common taxa identified groupings which could be related to depth and temperature. The seasonal occurrences of planktonic larvae of benthic taxa were found to be correlated with sea-bottom temperature in the winter as well as parameters of the sea-surface temperature. Possible interpretations of these data are discussed.

Comparisons of the behaviour of herring (Clupea harengus L.) were made in the light and dark by means of an infra-red sensitive TV system and video recording. Herring which were schooling in the light became less active in the dark, their swimming speed decreased, they tended to disperse and the proportion of gliding compared with swimming fish increased. Herring which were not schooling in the light increased their swimming speed in the dark.

When subjected to transient sound stimuli herring made fast-startle responses. The proportion of fish responding was lower in the dark. The directionality of the response (the proportion turning away from the sound source) was the same in the light and dark suggesting there was no visual component in the response.

The proportion of swimming and gliding fish affected both response rate and directionality. Gliding fish tended to have a higher response rate and better directionality than swimming fish, although this depended on the conditions of the experiment. The configuration of the body of swimming fish at the onset of a transient sound stimulus was important. Of the swimming fish, over 80% of the responders turned away from the direction in which the tip of the caudal fin was pointing at the onset of the stimulus. Gliding fish are in a better ‘neutral’ posture to initiate a startle response and to turn away from the sound source.

Comparisons of awareness (sensory thresholds) in the light and dark using startle responses are complicated by differences in the numbers of gliding and swimming fish.

In the most recent monograph of the marine planarians Wilhelmi (1909) described only one new species, viz. Procerodes dohrni, which nevertheless was strikingly similar to P. lobata (Schmidt, 1861). More recently Den Hartog (1968) has described inadequately a rather similar species, P. ireneae, and the taxonomic status of these three species is now somewhat confused, making proper identification difficult. For the present paper the available material of these species has been re-examined with the view of elucidating their taxonomic status.

The gross anatomy of the heart-body of the lugworm Arenicola grubii Clap, was described by Gamble & Ashworth (1900) and Ashworth (1904) who noted that it was also well developed in A. ecaudata Johnston (Ashworth, 1904) but was absent in A. claparedii Levinsen and A. cristata Stimpson. These authors noticed that there was no trace of a heart-body in young specimens of A. marina (L.) but that it was recognisable in worms measuring 65 mm or more in length. In such worms the heart-body tissue was described as consisting of two simple layers. In larger worms the layers are invaded by tissue resembling the wall of the heart and are probably invaginations of it. Dissection does suggest that the heart-body which lies only within the ventricle, is indeed formed by invaginations from the wall of the heart.

The Molpadiida is an order of sea cucumbers identified by their stout body, the posterior region narrowing to simulate a tail and the absence of tubefeet. Typically they inhabit muddy environments from shallow water to abyssal depths. In the past the great variability in the taxonomic characters of this order has led to the formation of many genera and species (Heding, 1931, 1935), but more recently it has become apparent that many diagnostic characters change markedly during the life history of these holothurians and as a result fewer species are now recognised (Deichmann, 1940; Pawson, 1977). In a revision of the Atlantic molpadiids Deichmann (1940) recorded just three species from the north-east Atlantic (Molpadia blakei, M. musculus and Hedingia albicans) with a further three species from the Arctic Ocean and Norwegian Sea (M. arctica, M. borealis and Eupyrgus scaber). To these Sibuet (1974) added the new genus and species Cherbonniera utriculus found in the Bay of Biscay.

Within a cohort of young copepods, the individual size or growth rate becomes increasingly diversified during the development. The longer the development, the greater the resulting anatomical or functional diversity, since the differences between fast growing and slow growing individuals increase with time. Different factors may contribute to this variability, such as genetic diversity and metabolic differences in the ability to utilize food resources.

Pelagic eggs and demersal eggs of teleosts both have osmotic concentrations similar to that of the maternal body fluids, less than half that of sea water. Pelagic eggs are buoyant because they contain such large quantities of this dilute aqueous fluid. While the demersal eggs of teleosts usually have a water content of 60–70%, the buoyant pelagic eggs of marine teleosts such as whiting, Norway pout, saithe, cod, haddock, turbot, dab, plaice, witch, long rough dab, halibut and sole typically have a very high water content (ca. 92 %) and a lipid content of 10–17% of egg dry weight. About 90% of the buoyancy of such eggs in sea water is caused by their high aqueous content, only about 10% being caused by lipid. The buoyant eggs of grenadier and ling have large oil globules and higher lipid contents, 27 and 35 % of dry weight respectively. Nevertheless, most of their buoyancy is provided by their high aqueous contents (89 and 81 % water). The high water content of pelagic eggs is brought about by a massive influx of water into the oocytes during meiotic maturation (ripening) after vitellogenesis but before ovulation. In cod and plaice, ripening is accompanied by a four- to five-fold increase in both water content and free amino-acids, and by a large influx of both potassium and sodium. In cod, free amino-acids contribute much more than these inorganic ions to the water influx and to the total osmotic concentration of the mature egg, but in plaice the relative contribution of inorganic ions approaches that of the free amino-acids.

Tagging data for 5959 bass, Dicentrarchus labrax L., released around England and Wales between 1970 and 1984 have been compiled and analysed to show seasonal distribution patterns and implied movements of populations in the southern North Sea, the central English Channel and the south-west and west coasts. Juvenile bass appear to remain near their nursery areas throughout the year, whilst adults show extensive migrations between summer feeding areas and winter pre-spawning areas, which are specific to local populations. Straying occasionally occurs between populations, but only at the ‘adolescent’ phase, and for management purposes local populations may be considered discrete.

A species of Eulalia, keying out as E. pusilla Örsted, 1843 in Fauvel (1923) and Hartmann-Schröder (1971), was collected at Plymouth in 1986. This species does not however agree with the original description, nor does it occur in the Danish waters from where E. pusilla was first described. The confusion apparently stems from Quatrefages (1865) and Saint-Joseph (1888) who both incorrectly applied Örsted's name to this more southerly species, the latter author providing the first accurate description.

The highly restricted ranges of many intertidal invertebrates, and the relative importance of physical and biological factors on settlement and subsequent mortality, have attracted much attention from ecologists. Most workers have concentrated on rocky shore communities, where patterns of zonation are often very clear (for reviews, see Stephenson & Stephenson, 1949, 1972; Southward, 1958; Lewis, 1955, 1961, 1964), whilst few have looked for such effects within saltmarshes (for reviews, see Long & Mason, 1983; Foster, In Press). Since most saltmarsh invertebrates are infaunal, patterns of zonation are not immediately obvious, but may be of particular interest; the influence of tidal regimes on invertebrate ranges may be more precise in sheltered saltmarsh habitats than on rocky shores, where exposure to wave action is a major confounding variable.

The analysis of the complex trophic relations characteristic of plankton communities is much simpler in an isolated body of water than in the open sea. In fact, in the open sea physical processes make many biological phenomena difficult to recognize, and advection and turbulence generally make it impossible to sample repetitively the same population of organisms for long periods of time.

Garfish (Beloniformes, Belonidae) are surface-dwelling, predatory fish characterized by elongate bodies and long beak-like jaws. Most are oceanic, but some species occur in estuaries and rivers. There are thirty-two species worldwide (Collette, 1982), of which until recently only one, Belone belone (L.) was known to be present in the waters of northern Europe. However, the existence of a second species, Belone svetovidovi Collette and Parin, was reported by Dorman (1984) from the south coast of Ireland. To date, thirty-one specimens of this fish have been captured in Courtmacsherry Bay, Co. Cork. This paper gives some details of these fish and how they may be distinguished from B. belone.

Haemoglobin is present, often at high concentration, dissolved in the blood of all small Pogonophora so far examined.

The haemoblobin of Siboglinum fiordicum resembles annelid and vestimentiferan haemoglobins in having subunits with molecular weights of 15000–16700 plus traces of 35000–40000 MW material. 5. fiordicum haemoglobin has 1 mol haem per 21500 g protein, and a similar lack of correspondence between subunits and mols of haem is shown by annelid and vestimentiferan haemoglobins. However, S. fiordicum haemoglobin differs considerably from annelid and vestimentiferan haemoglobins in other respects, even though the three groups are closely linked taxonomically. The haemoglobin of S. fiordicum has a lower apparent molecular weight (Mr = 3.5–4.0 x 105) than that of annelid haemoglobins (Mr = 3–4 x 108) when measured under the same conditions. Pogonophore blood examined with the electron microscope does not show the two-tiered hexagonal structure found in annelid and vestimentiferan haemoglobins. S. fiordicum haemoglobin also differs from annelid and vestimentiferan haemoglobins in amino acid composition.

The haemoglobins of the small pogonophores examined have a very high affinity for oxygen. The P 50 ranges from 0.36 Torr in diluted blood of S. fiordicum (15 °C) to 0.5–1.0 Torr in undiluted blood of S. atlanticum (10 °C) and s. fiordicum (15 °C). Only a slight Bohr effect was found. The high oxygen affinity can be related to the wide range of P o2 values experienced in the habitat and the need to transport oxygen to the deeply buried posterior end of the body that contains autotrophic endosymbiotic bacteria.