Aspects of the digestive cycle of Carcinus maenas have been studied by transmission and scanning electron microscopy, X-ray microanalysis and light microscopy. Movements of ingested material have been followed by feeding the crabs with Mytilus edulis (L.) labelled with colloidal particles of gold or thorium oxide.

Of nine northern European species of the Gadidae examined in the aquarium, or in cages in the sea, four produced sounds. The vocal species were the haddock, Melanogrammus aeglefinus (L.); the cod, Gadus morhua L.; the lythe, Pollachius pollachius (L.); and the tadpole-fish, Raniceps raninns (L.). The main differences between the calls of the vocal species lay in their temporal structure, all the calls being divisible into brief pulses of low frequency sound, repeated at different rates and in different groupings. Calls with this structure yielded spectra with a series of spaced harmonics, the frequency spacing depending upon the pulse repetition rate.

Sixteen additional species were dissected, and seven of these showed well developed muscles attached to the swimbladder, similar to those found in the four vocal species. The remaining nine species, together with the five non-vocal species examined in the aquarium, lacked the muscles.

The behavioural significance of the calls and the operation of the sound producing mechanism are discussed.

Proximate aspects of diel vertical migration in the freshwater and marine environment are compared using data from the literature. Examples of migrations in both environments are presented, from which it is concluded that relative changes in light intensity before sunrise and after sunset are primary causes of migrations. Experiments have shown that photoreactive behaviour is enhanced in the presence of predators but inhibited by shortage of food. These factors are called secondary causal factors. A hierarchy of causal factors is proposed. In lakes fish exudates suffice but in marine biotopes like bays, it is possible that fish have to be actually present for enhancement to take effect. To what extent the presented stimulus-response mechanism holds for mesopelagic animals in oceans is discussed on the basis of vertical distributions of euphausiids.

A survey has been made of the bottom fauna in ca. 10–50 m along the south coast of England, using a modified anchor-dredge. Particular attention has been paid to the molluscs (both living and dead) and to the echinoderms, only larger or more conspicuous members of other groups being identified.

Within the Channel there are considerable variations in temperature and other hydrographic conditions, and these are discussed in relation to their possible role as limiting factors in distribution. The fauna and bottom deposits of the different areas covered in the survey are briefly described.

Distribution trends are classified as:

(1) Species generally distributed in the Channel. This is the largest group, and includes three species reaching their northern limits in British waters.

(2) Species confined to the western parts of the Channel.

(a) Western species. Four or five species common at Plymouth in the 1920's, but now absent or very rare. Small numbers are found today only off the south Cornish coast, and those which occur in the North Sea are restricted to the north-western areas. Apart from one species, these forms are not at their geographical limits in the English Channel, and their occurrence may be partly related to the presence of ‘western’, but not necessarily Sagitta elegans, water.

(b) Cornubian species. These are near the northern end of their range, and occur quite commonly off the south Cornish coast, becoming progressively less common farther up-Channel. It is suggested that their distribution is related to an intolerance of the lower winter temperatures in the more eastern part of the Channel.

During recent years attention has been focused on the morphology of the bivalve digestive gland (Sumner, 1966a, b; Owen, 1970; Pal, 1971,1972) but there is little information concerning its role in the storage of energy reserves. Reid (1969) has suggested that in the horse clam, Tresus capax, digestive gland lipid may serve as an energy store which is depleted when food is scarce. Sastry (1966) and Sastry and Blake (1971) have shown that material stored in the digestive tissue of Aequipecten irradians is transferred to the gonad during gametogenesis and Vassallo (1973) has confirmed the transfer of lipid in Chlamys hericia. The digestive gland of My tilus edulis may also have a storage function and may therefore be involved in the utilisation of reserves during starvation. The present paper deals with seasonal changes in the biochemical composition of the digestive gland of M. edulis, and with changes induced by starvation and temperature stress.

The analysis of 35 bottom trawls taken on the slope in the Catalan Sea (western Mediterranean) has shown the existence of two different demersal fish assemblages occurring on the upper (350–650 m) and middle (1150–1300 m) slope. The middle slope assemblage is characterized by much higher values in some ecological parameters such biomass and mean fish weight, resulting from the dominance of middle to large size species (e.g. Alepocephalus rostratus, Trachyrhynchus trachyrhynchus, Mora mom). On the upper slope two different stations were considered, one inside and the other outside a submarine canyon. Only slight differences were found in species composition, and hence sample and species were not clearly separated by a correspondence analysis. However, some interesting ecological differences exist between these two stations. Much higher values in abundance and biomass inside the canyon were indicative of higher food availability there. Moreover, a drop in mean fish weight was also noted inside the canyon. The analysis of size distributions in the commonest species along the upper slope showed that the submarine canyon acts as a recruiting ground for some of them.

Polar benthic communities are subject to a range of disturbance levels from a variety of sources, principal amongst which is ice. This occurs in four main forms: the ice-foot, ice scour, anchor ice and fast ice, each of which influences benthos in a very different temporal and spatial manner. The four described forms of ice disturbance are all seasonal, but combined, influence communities throughout the year. The magnitude of ice mediated disturbance is often catastrophic and as a result both dominates benthic community structure and makes recolonization and development rates critical. This disturbance extremity results in high temporal and spatial heterogeneity, very low intertidal zone diversity and in places low mid–sublittoral diversity. It may also, however, be important in generating and maintaining the typically high sublittoral zone diversity observed at many polar localities. Intermediate frequencies or magnitudes of disturbance have been controversially discussed as important in maintaining diversity by prevention of space monopolization by overgrowth dominants in such environments as the deep sea. The shelf areas examined to date certainly suggest intermediate disturbance is important in maintaining polar sublittoral zone diversity. The combination of slow colonization and development with high frequencies of disturbance means most polar nearshore environments that have been described are permanently in a state of change or recovery.

The density of 18 species, measured by weighing them in sea water and in air, was found to vary widely. The weights of these fish in sea water ranged from about 7 % to less than 1 % of their air weights.

The Pacific oyster Crassostrea gigas (Mollusca: Bivalvia) was introduced to Ireland in 1965 and is farmed at many sites around the coast. The reproductive biology of 1377 oysters from two sites on the south coast of Ireland was examined from April 1996 until December 1997 for variations in maturation rate and condition indices. Qualitative data were compiled by staging gonadal development using histological sections. Environmental parameters of temperature, dissolved oxygen and chlorophyll-a levels, as well as parasites and pathology were monitored. Unusually high sea temperatures led to oysters in Dungarvan (site 1) spawning in both years of the study. Although sea temperatures were significantly higher, oysters in Cork Harbour (site 2) did not spawn but instead reached ripeness and then started a process of gametic degeneration called resorption. Lack of spawning was not attributed to environmental conditions monitored but was tentatively attributed to levels of pollutants in the water. Oyster condition in Cork Harbour was significantly affected by the presence of blistering due to tributyltin levels in the water and also by Polydora sp. (Polychaete) in the shell. Oyster condition in Dungarvan was not affected by the presence of the exotic species Mytilicola orientalis (Copepoda: Cyclopoida).

Imposex (the development of male sex organs on the female) has been studied in the European sting winkle, Ocenebra erinacea. In common with studies of other gonochoristic stenoglossan gastropods, the evidence gained from surveys of the south-west regions of England and Brittany (France) indicates that the phenomenon is a response to tributyltin (TBT) pollution. Close to sources of TBT, O. erinacea females exhibit structural abnormalities of the oviduct as a result of advanced imposex, including absence of a genital papilla and a normal vulva, a deformed bursa copulatrix and the presence of a longitudinal split. Copulation and capsule formation would appear to be inhibited in the worst-affected females. Such curtailment of breeding activity would result in population decline: direct evidence of the extinction of O. erinacea close to harbours, as is known for N. lapillus, is generally wanting for British shores, but the decline of the species in the Bay of Arcachon in France is attributable to TBT pollution.

Prokaryote organisms have been found in the gills of six species of Thyasiridae, collected in the north-east Atlantic region, from depths of 15 to 1250 m. The fine structure of the gill epithelia and the symbiotic Gram-negative bacteria is described. The bacteria occur extracellularly, between a thin cuticle and the apical membrane of the host cell. This differs from the intracellular position of bacterial symbionts in two lucinid species, Lucinoma borealis and Myrtea spinifera, and many other bivalves already known to harbour symbionts in their gills. Four species of Thyasiridae and Diplodonta rotundata, a member of the closely related family Ungulinidae, were found to lack gill symbionts.

In recent years there have been several accounts of the occurrence of diclidophoroidean trematodes parasitic on the gills of fishes, e.g. Price (1943), Sproston (1946), Dawes (1947), Brinkmann (1952), and Chauhan (1953), and these accounts have included descriptions of the morphology of the parasites. The distribution records have revealed a generally high degree of host specificity and, in some species, a preference even for certain gill arches of the particular hosts, while the morphological descriptions have shown that there is a considerable variation in the form of the parasites, extending to various degrees of deviation from bilateral symmetry (PI. I, figs. 1–11). These morpho-logical variations are present in spite of the fact that the different parasites occupy such broadly similar habitats in the gill chambers of their respective hosts. But, as far as I am aware, this is the first attempt to investigate the distribution and morphology of the parasites in relation to their micro-habitats.

Spatial pattern of settlement of cyprids of the barnacleBalanus balanoides (L.) was examined from photographs taken every low tide during the first 20 days of the settlement season. The locations of pits and cracks and the bases of detached adults were mapped in order to measure specificity of settlement in relation to surface contour and chemical cues associated with conspecifics. Cyprids were identified as to their date of settlement. Distances to nearest neighbours were computed for newly settling cyprids relative to each other, for newly settling cyprids relative to previously settled cyprids, and for newly settling cyprids relative to newly metamorphosed spat.

By comparing the two species of Amphiura in controlled, directional bottom current flows, clear differences of behaviour can be demonstrated. These differences have been shown to be associated with two quite distinct feeding methods. Amphiura filiformis holds the arms up into the current flow with a rheotactic response to current direction and feeds by trapping both non-living particulate suspended matter and phytoplankton. Amphiura chiajei does not show this response and feeds exclusively on deposited matter on the sediment surface. Both species have modifications of the podia associated with the different methods of feeding. Estimates of growth rate, longevity and oxygen uptake suggest that Amphiura filiformis is a rapidly growing species with a high metabolic rate and food requirement, whereas Amphiura chiajei is slow growing and long-lived with a low metabolic rate. The environmental requirements of the two species are discussed.

The amplitude and phase of tidal characteristics in the English Channel have been described both using numerical models (Grijalva, 1962; Hyacinthe & Kravtchenko, 1967) and a hydraulic model on a rotating table (Chabert d'Hières & le Provost, 1970). The aim behind the development of the numerical model described here is first to derive an accurate representation of the principal lunar semi-diurnal (M2) tide in the English Channel and then to use the currents generated by the tidal input to determine the tidal circulation patterns and residual flow through the English Channel. A test of the model must be its ability to reproduce the known clockwise eddy in Lyme Bay and the south-ward flow either side of Portland Bill. If these known tidal residuals can be reproduced then the model may help to elucidate residuals in other regions where the flow is unknown. In addition to deriving the mean tidal velocities, horizontal distributions for the mean squared and cubed values are calculated and the importance of these distributions in determining the nature of the bottom and the degree of stratification of the water column in summer is demonstrated.

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).

This is the third and concluding part of an investigation into defensive mechanisms in some British gastropods. The first part (Thompson & Slinn, 1959) dealt with a single species of opisthobranch, Pleurobranchus membranaceus, which proved able to secrete a strong acid if disturbed. The second part (Thompson, 1960 a) recorded further instances of acid secretion. The present paper describes the remainder of my work on opisthobranchs.

A study has been made of the nitrogenous compounds excreted by Calanus helgolandicus (Claus) collected at Plymouth.

Most of the excreted nitrogen is in the form of ammonia which accounts for 60–100% (average 74.3%) of the total, and some of the remainder may be lost as urea. There is no evidence for the excretion of measurable amounts of amino acids.

Whether the animals are starved or fed they are primarily ammonotelic, and the quantity of ammonia produced at 10° C (3.33 μg/g. dry body wt/day) is not significantly changed when the animals are used at an abnormally high experimental density. This latter condition does, however, lead to the production of large quantities of additional nitrogenous substances that give a positive reaction with ninhydrin.

Introduction

The amounts of nitrogen excreted by zooplankton have been measured by several workers. Harris (1959) used the method of Riley (1953) to estimate the copious quantities of ammonia produced by animals (mainly Acartia tonsa and A. clausi) collected from Long Island Sound; Beers (1964), in laboratory experiments with the chaetognath Sagitta hispida, estimated the excreted ammonia by the procedure of Kruse & Mellon (1952); and Corner, Cowey & Marshall (1965) determined the ammonia excreted by Calanus helgolandicus and C. finmarchicus, using a ninhydrin technique described by Moore & Stein (1954). The methods employed by Harris and by Beers are specific for ammonia: that used by Corner et al. estimates nitrogenous substances (e.g. amino acids) in addition to ammonia, but certain tests were made which seemed to exclude the possibility that these substances contributed significantly to the nitrogen excreted by the animals.

Adult barnacles adhere to surfaces by a secretion released on to or forced beneath the bases. This secretion has been called barnacle cement. Carderelli (1968) calculated from crude experiments that the tensile strength of Balanus eburneus exceeded 50,000 p.si., but apart from this work no other data exist on the adhesive properties of barnacle cement. More studies have been undertaken on the biochemical composition of cement (Carderelli, 1968; Saroyan et al., 1970; Cook, 1970), but the results are somewhat contradictory.

A number of studies exist on the seasonal cycles of body weight and tissue biochemistry of several species of bivalve from the Clyde Sea area (Ansell & Trevallion, 1967; Ansell, 1974, et seq), including two members of the Pectinidae, namely Chlamys septemradiata (Müller) (Ansell, 1974) and Pecten maximus L. (Comely, 1974). Some comparative data are available for Chlamys opercularis (L.) from Manx waters (Soemodihardjo, 1974) and for P. maximus from the north Irish Sea (Stanley, 1967).