Spray-dried Nannochloris sp. and Tetraselmis suecica were fed to larvae of the Manila clam (Tapes philippinarum).

These dried diets supported growth equal to, or greater than, their live algal counter-parts, but less than a control diet, a mixture of two algae species of known high nutritional value (Chaetocems calcitrans and T-ISO).

Larvae were grown through to metamorphosis on the dried Nannochloris sp. diet in 21 days, compared with 8–11 days with the control diet. Using dried Nannochloris, it was shown that T. philippinarum larvae do not have an essential requirement for long-chain (20 and 22C) polyunsaturated fatty acids, but are able to synthesize them from shorter chain (18C) fatty acids present in the diet. The higher total carbohydrate content of the dried algae was reflected in the larvae feeding on this diet.

Advantages and disadvantages of methods used to estimate area of individual secondary lamellae are discussed. Particular attention is given to explain the method which regards filaments as triangles and lamellae as rectangles. Dangers of some injection methods assuming that the whole lamellar microcirculation is equally involved in gas exchange are also emphasized. It is concluded that there is a need for comparisons of results when different methods are applied to the same material.

The anatomy and behaviour of the oncomiracidia of Kuhnia scombri, K. sprostonae and Grubea cochlear, related mazocraeid monogeneans from the gill chamber of the mackerel, Scomber scombrus, caught off Plymouth are compared. K. sprostonae and G. cochlear are new records at Plymouth. The most important anatomical difference between these larvae is that those of Kuhnia spp. possess a pair of pigment-shielded eyes which are lacking in G. cochlear. The freshly hatched larvae of Kuhnia spp. are strongly photopositive but this response wanes after about 1 h in K. scombri and 1–5 h in K. sprostonae. No response to light was detected in larvae of G. cochlear. Most older larvae of Kuhnia spp. and of G. cochlear swim continuously upwards and downwards, even in ‘darkness’, indicating an alternation between positive and negative geotropism. The larvae of Kuhnia spp. possess angular cells (?) of unknown function close to the pharynx. The larvae of all three species contain prominent anterior glands and lipid droplets; the latter are depleted during their long free-swimming lives (up to 36 h in Kuhnia spp. at 13–14°C).

Unlike other sea turtles, the leatherback Dermochelys coriacea forages widely in temperate waters during summer and dives to abyssal depths (>1000 m) where temperatures are low. There is strong anatomical plus limited physiological evidence in favour of at least facultative endothermy. The lipids of leatherbacks exhibit features which are consistent with maintenance of a core temperature above ambient levels when in cool waters. The lipid of flipper adipose tissue freezes at a lower temperature than lipids extracted from the blubber lining carapace and plastron. Lipid freezing points in leatherbacks are lower than for tropical caimans or terrestrial sheep, but higher than for lipids taken from the blubber of a grey seal. Leatherback adipose tissues show levels of unsaturation in neutral lipid fractions intermediate between those of seals and sheep.

Gigantocypris is a good swimmer, capable of moving fast enough to overtake a variety of zooplanktonic Crustacea and chaetognaths. It swims smoothly without violent accelerations and decelerations. Previous reports of unstable weak swimming in this species stem from the study of overheated animals; Gigantocypris is stenothermal, adversely affected at temperatures above about 15°C. Gigantocypris is nearly neutrally buoyant (sinking speed 0·2 mm s−1) and is capable of hovering for long periods with the aid of slight movements of the propulsive antennae. When swimming quickly Gigantocypris achieves an average speed of 164 mm s−1 (9·6 mm body length; 391 antennal beats min−1) at 12·5°C. It is unlikely that Gigantocypris performs significant diurnal vertical migrations. The heart of Gigantocypris is large and beats at ca 100 beats min−1. Macrocypridina is a faster swimmer (<52·3 mm s−1 (8·3 mm body length) at 12·5°C with an antennal frequency of 583 beats s−1), but each beat is accompanied by great accelerations and decelerations. Macrocypridina is dense, sinking at 40 mm s−1. Macrocypridina is eurythermal, its swimming speed increasing steadily between 11·5 and 20°C.

The annual reproductive and somatic cycles of the brittlestar Acrocnida brachiata are described using gonad and gut indices for intertidal and subtidal populations in the Bay of Douarnenez, France. Oocyte size frequency diagrams complement the gonad study in the subtidal population. Clearly marked reproductive cycles are defined in both populations. Accelerated gonad growth takes place in spring and the gonads reach the peak of development in May-June each year. Spawning is completed by the end of August. Oocytes reach a mean diameter of 150 μm and a new generation of oocytes appaears in the ovaries during the spawning period. The gut indices show a clear inverse relationship with the gonad indices in the intertidal population, but this relation is not well revealed in the subtidal population.

Haliotis tuberculata L. densities and population distributions were assessed for 13 sublittoral sites around the coasts of Jersey, Channel Isles using SCUBA techniques. Twenty 1 m2 quadrats were assessed at each site at 5 m below lowest spring tide level (LSTL). Mean densities at each site ranged from 0·05 animals m−2 to 2·35 animals m−2, while the overall mean for the whole island was 0·79 animals m−2 (s.e.=0·24). Population density (D) declined with increasing mean animal length (LTH). The slope of the equation relating loge D to loge LTH was -6·92. Data collected at 2 m, 5 m, 8 m and 10 m below LSTL at two sites showed no trend in mean animal length with depth at one of the sites, but it did increase slightly with depth (1·3 mm nr−1) at the other.

Chlorophyll analysis and methods of direct observation of rock surfaces under the SEM were used to estimate composition and abundance of epilithic microbial taxa. Effectiveness of different chlorophyll extraction techniques was assessed. Extraction from ground and intact rock was compared using both hot methanol and acetone extraction methods. Hot methanol extraction from intact rock provided the most accurate and precise estimates of chlorophyll content. SEM preparation methods were compared. Microbial taxa were counted under the SEM from cryostage, critically point dried and air-dried material. It was concluded that air drying was the most appropriate preparation method for SEM observation. Air drying provides reasonable estimates of microbial composition and abundance and was less time consuming so allowing an adequate number of samples to be analysed. Cumulative species number with sampling effort curves were used to establish minimal sample sizes with respect to estimates of species number. Sequential estimates of mean abundance with increasing sample size were used to determine the effects of increasing sample size on estimates of abundance of the dominant taxa. These estimates were compared at different times of the year and for two different locations. Microbial communities were found to be extremely patchy in distribution. However, sample sizes required to give good estimates of taxa number and abundance were established. These estimates were found to be similar for the main taxa at different times of the year and at different locations.

The population structure of the common shrimp Crangon crangon (L.) in British waters is investigated. Samples were collected from 31 sites along the coasts of England, Wales, Holland, Belgium and France. Using a morphometric analysis it is concluded that English and Welsh waters hold six distinct populations. Animals belonging to the same population are found on the opposing English and continental coasts in the southern North Sea and English Channel which indicates that the avoidance of offshore waters is not isolating the shrimps. The boundaries between the populations are found to correspond with the boundaries between major plankton assemblages. It is suggested that the populations are isolated by the reduced dispersal of the planktonic larvae across fronts where bodies of water with different physical properties meet but incompletely mix.

Differences in average body size among allopatric and sympatric populations of hydrobiid mudsnails have been interpreted as the consequence of interspecific competitive interactions. Recently, however, doubts have been expressed concerning the certainty with which size differences can be ascribed simply to character displacement. Other environmental factors are known to influence body size in hydrobiids. In the present study one of these, sediment type, was investigated.

Average body weight of Hydrobia ulvae (Pennant) living on fine mud was consistently higher than that of members of the same species living on adjacent muddy sand. Snails were transplanted from one sediment type to the other, confined within cages, and their growth rates compared with those of control animals caged on their native sediment. The results of this experiment suggested that substrate type is one factor controlling body size, but the inconclusive nature of the results indicate that others are also involved.

The swimbladder is recognized as responsible for a major part of the acoustic backscattering from fish. In most fishes it has the function of a buoyancy regulator but in others its main function is rather unclear. Based on methods for exact mapping of the swimbladder shape, observations of deviations from normal appearance and shape are discussed in relation to possible effects on target strength. Evidence for both periodic variations, as from uncompensated vertical migrations, and seasonal variations, caused by the fat cycle and gonad development, are presented.

Hermit crabs use gastropod shells to protect their bodies and developing eggs; an inadequate supply of shells of the appropriate size will, therefore, adversely affect their growth, fecundity and longevity. Since the supply of shells is commonly limited, mechanisms that help to reduce these adverse effects will be selectively advantageous. In Pagurus bernhardus it is suggested that two mechanisms have evolved in this respect: larval settlement is encouraged in the littoral zone where gastropod species are diverse and numerous and where the youngest hermits will find growth potentially unrestricted; and females breed within their first year of life and at a size substantially below that which could be attained in the shells commonly available to them. This ‘precocious’ breeding is suggested to be an adaptation enabling hermits to overcome the problems of shell-limitation, since it frees females of the need to attain a specific age or size before reproducing - a situation which would be perilous when large shells are scarce. Males of a similar age are freed from competition for the larger shells as a result of this strategy, since the growth of the females is suppressed while they are ovigerous.

The swimming behaviour of Corophium volutator from Wales and East Anglia was investigated to establish whether differences apparent from two previous studies are real or artefacts of the different techniques used. Swimming C. volutator were caught in a Welsh estuary in the summer, but only rarely in the autumn and winter, and in both daylight and darkness. In simulated tidal conditions in the laboratory C. volutator from two sites in East Anglia never swam, while those from Wales swam whenever the substratum was immersed, in daylight and darkness, mostly on the ebb tide and in winter. The unnatural swimming in winter may have been stimulated by laboratory conditions, but the East Anglian amphipods were not so affected. The tidal swimming rhythm is different to east coast C. volutator which only swim at night. This difference may be related to the time of spring tides, when most swimming occurs. In Wales high water of spring tides may occur only in daylight in summer and nocturnal swimming may not be possible. The ebb tide swimming by C. volutator in Wales contrasts with the flood and ebb swimming of east coast amphipods and may reflect differences in their habitats. The former were collected close to the sea while the latter were 15 km up a narrow estuary and may represent a sub-population of amphipods with a disposition to swim early (on the flood tide) enabling them to colonise upstream habitats.

Adult plaice (Pleuronectes platessa L.) in the southern North Sea use selective tidal stream transport to migrate between their summer feeding grounds and winter spawning grounds. The fish come up into midwater when the tidal stream is flowing in one direction, but remain on the bottom when it is flowing in the opposite direction. This behaviour can theoretically save energy, which can be used for growth or reproduction. Alternatively, it may provide a transport system by means of which fish that have no ability to navigate over long distances can be conveyed reliably between their feeding grounds and spawning grounds.

This ultrastructural investigation of gametogenesis in a deep-sea anemone of the Bay of Biscay trawled around 2000 m depth, contributes to the knowledge of biology and strategy of reproduction of deep-sea benthos.

This sea anemone is dioecious. The sperm appears very similar to those of shallow water sea anemones of the genus, Calliactis. The ultrastructural investigation of oogenesis allows the characteristics of the stages of previtellogenesis and vitellogenesis to be defined. The latter begins with a period of lipogenesis correlated with the formation of a trophonema. Mature oocytes measure up to 180 (im in diameter. Study of spermatogenesis and oogenesis reveals that spawning occurs in April/May. In males, the main area of testicular cysts, full of sperm, reaches maximal development from March to May and, in females, the percentage of mature oocytes decreases from 33% in April to 1% in May.

Spawning may be induced by the advent in the deep-sea of the products of the spring phytoplankton bloom. This period of spawning, during the increased deposition of organic matter to the deep-sea floor, may be an advantageous strategy for early development of Paracalliactis.

Examination of the reproductive biology of the abyssal seastar Dytaster grandis taken at different times of the year in the NE Atlantic suggests seasonal reproduction that is related to the seasonal pulse of phytodetritus to the deep-sea floor. Although this seastar is an omnivore, the availability of this labile organic material may fuel vitellogenesis during the summer and autumn months. The egg size suggests planktotrophic larval development. Spawning occurs in the early part of each year to allow the zygote to develop into a feeding larva to coincide with the downward flux of phytodetritus. Thus the flux of detritus may constitute an environmental forcing pressure at least at two points in the life history of D. grandis.

Activity patterns of limpets were studied at two adjacent sites in an Irish sea lough, Lough Hyne, in order to relate timing of activity to physical and biological influences. Activity was suppressed during heavy rainfall, and osmotic stress from dilution appears to have led to increased mortality in transplanted limpets. Activity increased as tides progressed from neaps to springs, and for limpets low on the shore it was enhanced by wave action. It is suggested that lack of activity in calm water may reduce predation pressure from crabs, which caused high mortality in transplanted limpets. Either low relative humidity or dryness of the rock diminished activity of low-water limpets. Differences in feeding activity between low-water limpets and high-water limpets may relate to food supply, since more food was available low on the shore, and the guts of low-water limpets contained more diatoms than those of high-water individuals. Differences between the two sites are at present unexplained but may relate to differences in micro habitats.

In early June 1988, an extensive bloom of Phaeocystis sp. (29xlO6 cells 1−1) was observed in the eastern Irish Sea along the North Wales coast. Chlorophylls, carotenoids, free amino acids, fatty acids, vitamin C, carbon and nitrogen were measured in particles from three size categories (<22 μm, 22–100 μm and 100–200 μm) at a station 13 miles off the coast line. Phaeocystis sp. formed 99% of the total particle stock below 22 μm and was characterized by (1) the presence of chlorophyll c3, (2) the dominance of fucoxanthin over 19'- acyloxyfucoxanthins, (3) the presence of C18:5 fatty acid at trace levels and (4) different proportions of amino acids compared to those measured in particles greater than 22 μm. These larger particles were dominated by diatoms, dinoflagellates and ciliates. The poor nutritional value of Phaeocystis sp. for herbivorous zooplankton was characterised by its low content of polyunsaturated fatty acids and vitamin C. Comparison between the chemical composition of Phaeocystis sp. and copepod faecal pellets showed that the copepods were feeding predominantly on other phytoplankton.

Skeletal growth banding has been studied in the vertebral arm ossicles of the shallowwater brittle stars Ophiothrix fragilis, Amphiura filiformis, A. chiajei, Ophiura ophiura and O.

albida collected from near Oban. Scanning electron microscopy of ossicle microstructure show the bands reflect differences in stereom porosity and surface relief on the surface of the wing-like fossae of the ossicle. The evidence supports the interpretation of the bands as annual growth markers, with coarse-pored stereom laid down during periods of active growth in summer/autumn whilst finer-pored stereom, that often forms ‘breaking wave’- like ridges, is formed during periods of slow or negligible skeletal growth during the rest of the year. Growth curves fitted to growth ring measurements indicate three contrasting growth strategies amongst the species examined. These data generally support recent interpretations of demographic structure reached from studies of size frequencies in samples collected from other areas in the NE Atlantic range of these species.

A laboratory study simulating herbivorous feeding was carried out with the marine crustacean Neomysis integer (Leach) and the dinoflagellate Scrippsiella trochoidea (Stein). Analyses of the total fatty acids, sterols and fatty alcohols in the food and faecal material, and in the animal tissue, have allowed the detailed changes in the dietary lipids during feeding to be characterised.

The results show this feeding leads to a net decrease in total lipid in the material passing through the gut of the animal, particularly due to the bioassimilation of fatty acids. All fatty acid saturation classes are assimilated but the mono-unsaturated and particularly polyunsaturated fatty acids are preferentially assimilated over others. Herbivorous feeding does, however, lead to the quantitative and relative increase in ‘bacterial’-type odd C number branched-chain fatty acids in the faecal material.