Veliger larvae of the nudibranch mollusc Adalaria proxima are triggered to metamorphose to the benthic form by the adult prey bryozoan, Electro pilosa. Ion substitution and supplementation experiments with artificial sea water (ASW) have, however, shown that metamorphosis can be induced by elevation of the potassium ion concentration alone. Approximately 19 mM K+ASW (10 mM ‘excess’) was found to elicit maximal metamorphic responses: 29 and 39 mM K+ASW had no inductive effect. Choline chloride was also found to induce metamorphosis in a dose-dependent manner, with lO M ineffective, 10 M approximately threshold, and 5×10 M to 10 M optimal. Concentrations of choline >10 M were sub-lethally toxic. That the absence of larval metamorphosis on exposure to 29 and 39 mM K ASW was due to inhibition is inferred from interaction experiments with choline: at these concentrations of K, metamorphosis in response to choline could be abolished. Timed-exposure experiments indicated that artificial induction elicited by elevated K and choline involve either separate mechanisms, or different parts of the same pathway. Thus, whilst larvae required to be continuously exposed to 19 mM K ASW in order to complete metamorphosis, those exposed to 10 M choline would subsequently complete development in normal ASW following only 1–2 h exposure to the inducer. Preliminary experiments failed to specify further the nature of the natural inducer, beyond the confirmation that live intact colonies of the bryozoan Electro pilosa will trigger larvae to metamorphose.

The dynamics of clearance, segregation and elimination of a marine bacterium, Moraxella sp., by the shore crab, Carcinus maenas (L.) has been studied utilizing fluorescent and radiolabelling techniques. In addition to the gills, the hepatopancreas was a major site of bacterial accumulation with sequestration occurring within haemocyte clumps and groups of stationary cells in this organ. The heart, excretory organ and subcuticular tissues also incorporated bacteria, but to a lesser extent. By the first day post-injection, many of the segregated micro-organisms had been removed from the organs. This latter process was not due to the exodus of laden haemocytes or of intact cell clumps from the host but seemed to result from lytic action by the host blood cells. Little material arising from such bacterial/haemocytic interaction was, however, immediately excreted, and much was relocated in the general body tissues as well as the gill nephrocytes.

Seasonal changes in the assemblage structure of dominant epipelic diatoms were studied along a transect crossing a salt marsh, sandflat, and mudflat of an estuarine intertidal shore at Berrow Flats, Somerset, UK. Seasonal changes in cell numbers displayed different patterns in the salt marsh and sandflat/mudflat. At salt marsh sites highest numbers of individuals were recorded in summer followed by a smaller autumn growth, while in the sandflat lower numbers showed no seasonal pattern. Repeated annual patterns in the succession of taxa were not observed as environmental conditions changed at the study site with time. Measurements of salinity, pH, interstitial water content, air and soil temperature were taken together with the diatom samples. A canonical correspondence analysis was employed to relate seasonal changes in assemblage structure to measured environmental variables. Total percentage variation in the first four axes of the species/site-environmental biplots ranged between 54 and 66°. In winter, sites and species separated most significantly along gradients of salinity and levels of organic matter. In spring and autumn, interstitial water content became a more significant environmental variable. By summer steep gradients in pH, levels of organic matter, and hypersaline conditions separated sites and assemblages into more discrete groups when compared to the more even spread of points in the other seasons. The results indicate that different combinations of environmental variables influence diatom assemblage structure seasonally.

The exposure of two species of talitrid amphipods (Orchestia gammarellus and Orchestia mediterranea) to a range of zinc and copper concentrations in solution has enabled the categorization of the mode of metal accumulation adopted by these supralittoral amphipods. Both species showed net accumulation of dissolved zinc and copper at all experimental exposures between 20 and 1000 μig Zng 1 and 13 and 1000 μg Cu 1 in artificial sea-water. Studies using Zn have shown that the zinc uptake rates of both species (0·430 μg Zn g d, SE 0·032 and 0·408 µg Zn g d, SE 0·073 for O. gammarellus and O. mediterranea respectively at 10°C in 31·6 μg Zn 1) are not significantly different, and are low in comparison with other crustaceans. Laboratory results are related to field conditions, and it is concluded that Firth of Clyde O. gammarellus are more dependent upon a food source in order to meet both their copper and zinc requirements than are O. mediterranea which are able to obtain sufficient metabolic copper from solution. The use of talitrid amphipods in zinc and copper biomonitoring programmes is also discussed.

The population biology of the crab Liocarcinus depurator was studied for one year in the mussel raft culture areas of the Ria de Arousa. The density and biomass of this species is much higher in the raft areas, especially in the outer part of the ria, than in the central channel area. Maximum abundance occurred during the winter months (up to 8-80 g wet weight m and 0-44 individuals m.

Maturity size in females was set at 28-30 mm carapace width, (based on ovigerous females) and is attained in the first year of life. The ovigerous females were most abundant in January (approximately 70% of the mature females), but another less important maximum value was observed in May, attributable to a second spawning. Modifications in the sex ratio from 1:1 affected individuals larger than the maturity size during the season when there was a greater number of ovigerous females present. Data on sex ratio and breeding cycle indicate that ovigerous females move towards the raft areas located in the outer part of the ria. Trawl recruitment took place in the stations located in the outer Ria, and mainly in August-September, although it continued to a lesser extent in autumn.

The Von Bertalanffy growth function was fitted to both sexes in the two outer stations. Growth rate was higher in males than in females, while variability between stations was less important. However the growth rate and reproductive output of L. depurator in the Ria de Arousa was higher than in populations from other geographical areas, possibly because of the availability of food from the rafts and or the oceanographic conditions in the ria.

Strombidinopsis species were collected from theGulf of Alaska, Gulf of Mexico, Caribbean Sea, Gulf of Maine, and Barents Sea. Six strains were conservatively placed in six species: Strombidinopsis chilorhax sp. nov.; Strombidinopsis batos sp. nov.; Strombidinopsis sphaira sp. nov.;Strombidinopsis cercionis sp. nov.;Strombidinopsis acuminatum Fauré-Fremiet, 1924; and Strombidinopsis spiniferum (Leegaard, 1915) comb. nov. Based on the characters of these species, the diagnosis of the genus Strombidinopsis was revised.

Relationships between wet body weight, dry body weight and ash-free dry body weight (AFDW) were established for the aspidochirote sea cucumber Holothuria forskali (Echinodermata: Holothuroidea); a wetdry weight ratio of 6–38:1 was found. Length-weight relations were also determined. Low oxygen tensions and mechanical trauma induced H. forskali to eviscerate (70% of individuals tested). Respiratory measurements of intact and eviscerated sea cucumbers were determined at 17°C. For intact animals, oxygen consumption (ul h1) was directly related to AFDW (the slope of the regression line, b=0–60), whereas weight-specific oxygen consumption (Vo2; ul g1AFDW h) was inversely related to AFDW (b=0–54). Oxygen consumption of eviscerated sea cucumbers was independent of AFDW (b=0-\5), but Vo 2 was inversely related to AFDW (t–0–85). There were no significant differences between the respiratory rates of intact and eviscerated individuals, indicating that H. forskali is not so dependent upon respiratory trees for oxygen uptake as previously assumed.

The American oyster drill, Urosalpinx cinerea introduced to UK waters around the turn of the century, flourished in the Essex oyster grounds until the 1970s. Recent observations, 1987–1990, made in Goldhanger Creek, River Blackwater, indicate that the population level has been reduced to the point of scarcity and that those individuals remaining are old. All females examined exhibited imposex. In most, this masculinizing syndrome was developed to an advanced state that involved oviducal malformation; copulation and egg capsule formation are thought to have been inhibited and hence such affected females were sterile. Other, probably very old, females appeared infertile because of senility. No viable spawn was observed during the four summers of 1987 – 1990.

Two new Appendicularians: Inopinata inflata gen. nov., sp. nov. and Mesopelagicn caudaornata gen. nov., sp. nov., from the family Oikopleuridae (Lohmann 1915), subfamily Oikopleurinae (Lohmann 1896a), are described from specimens collected at mesopelagic depths (660–840 m) in Bahamian waters by the ‘Johnson-Sea-Link’ manned submersibles.

A meeting on Plant-Animal Interactions in the Marine Benthos was held in Liverpool in September 1990, organized by the Sy sterna tics Association in their Symposium Series, and supported by the Marine Biological Association. The following six papers were first presented at this meeting:

The occurrence of a population of Ophelia bicornis has been recorded at a site which may be the most northerly for the species, and the only one within the United Kingdom. The irregular and patchy distribution of the population is described and reviewed in relation to other recorded occurrences of the polychaete.

Experiments on herring (Clupea harengus L.), sprat (Sprattus sprattus (L.)) and whiting (Merlangius merlangus (L.)) showed that when these fish make rapid swimming movements, such movements are preceded by fast pressure pulses in the surrounding sea water. Thefirst (a) phases of these pulses had durations of from 1–5 to 3–5 ms. The pulses could be excited in free-swimming fish by both visual and auditory stimuli and the latencies to the latter ranged from 5 to 8–5 ms. Identical pulses could be elicited by giving electrical stimuli to anaesthetized fish; these pulses had latencies from 34 to 7 ms.

The pressure fields around the fish were measured on suspended anaesthetized fish stimulated electrically. At any instant the fields of the fast pulses produced by whiting had the same polarity at all positions round the fish and pressure decayed inversely with the 1–5 powerof distance. The a phase of the fast pulse was usually a decompression.

The fields around a stimulated herring were different. The pressures on both sides oppositethe centre of the fish were of one polarity while those around the head and the tail were of the opposite polarity, the pattern of pressure being symmetrical about the long axis of the fish.In our experiments the a phase opposite the centre of the fish was always a compression. The amplitudes of these pulses declined with distance by the power of 2–5. In all species in our experiments the fast pulses were followed by slower pulses associated with swimming movements; these slower pulses had opposite polarities at corresponding points on the two sides of the fish.

The hypobranchial gland ofMorula gramilata (Duclos) has been morphologically and histochemically characterized. The marginal zones of the gland have mucocytes and eosinophil cells while the median region has in addition ciliated cells and gland cells. Neurosensory cells are also present. Two types of mucous cells have been identified. Type I secrete a diastase-resistant, neutral mucopolysaccharide, while type II secrete PAS unreactive, strongly acidic and highly sulphated mucins. Exposure to low temperatures, ultraviolet rays and irritants resulted in the production of a purple dye.

Naturally spawned bass, Dicentrarchus labrax, eggs were incubated from fertilization at 15 temperatures from 6·8–20·6°C, and the developmental process was categorised into seven stages. Times from fertilization to the midpoints of each stage were calculated at each temperature. Knowledge of the developmental stage and incubation temperature was used to derive predictive relationships with which to age eggs. Minimum precision of age prediction was ±18 h. The first developmental stage was divided into six substages, and temperature-stage relationships derived to improve the precision of ageing to a minimum of ±1·75 h during early development. Bass eggs failed to hatch at temperatures below 9·7°C and above 16·8°C; this observation is discussed with reference to the developmental process.

The various steps involved in experimental investigations of the causes of observed ecological patterns are examined. A sequence of different steps (observation, model, hypothesis, null hypothesis, test) is identifiable. The logical necessity for distinguishing and evaluating each of these steps is discussed. The potential usefulness of explicit recognition of the logical relationships between the various parts of the procedure is evaluated by reference to experimental studies to determine the causes of boundaries of vertical distribution of macro-algae in rocky intertidal habitats. Pitfalls of experimental procedures can sometimes be recognized as failures in the logical progress from one part to the next in the sequence of steps necessary in any study. Particularly important is the early recognition of the existence of many, potentially conflicting, but sometimes interactive, models to account for any observed pattern. Greater attention to the relation-ships between the components of the logical structure of an experimental study might aid in reduction of errors in the design, analysis and interpretation of ecological experimental data.

Microbial films represent the site at which grazers exert their influence upon the recruitment of settling macroalgae and animals. The overall purpose of this study of seasonal and spatial variation in abundance and composition of epilithic microbial films was to relate such patterns to macrobenthic community dynamics within the Fucus-bar- nacle mosaic characteristic of moderately exposed rocky shores on the Isle of Man. Additionally selective grazing in Patella vulgata was examined by comparing dietary and epilithic microalgal assemblages and how this varied seasonally and spatially within the mosaic. Chlorophyll analysis was used as an index of microalgal standing crop while SEM allowed in situ estimation of microalgal abundance.

Changes in dietary lipids were investigated in laboratory feeding experiments simulating herbivorous and coprophagous modes of feeding in the bivalve mollusc Scrobicularia plana (da Costa). The dinoflagellate Scrippsiella trochoidea (Stein) was used as the food in herbivory experiments while faeces from the crustaceanNeomysis integer (Leach) feeding on Scrippsiella were used as the food in coprophagy experiments. Changes in dietary total fatty acids, sterols and fatty alcohols were characterised by analyses of the food, faeces andanimal tissues using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS).

There is a net decrease in the total lipid of the digested material during both herbivory and coprophagy. However, while fatty acids are assimilated, sterols are contributed to the faeces, leading to a decrease in the fatty acid:sterol (FAST) ratio of the digested material. Coprophagy decreases the ratio still further, such that faeces have a FAST ratio of <1

Scrobicularia preferentially assimilates dietary polyunsaturated fatty acids (PUFAs). Reworking of sedimentary material (as in coprophagy) will lead to PUFA-deficient sedimentary fatty acid distributions. Both herbivory and coprophagy lead to relative increases in 'bacterial' odd carbon-number normal and branched fatty acids in the digested material, though not the 'bacterial' marker 18:1 Benthic molluscan feeding, particularly coprophagy, contributes partly to the 'bacterial' fatty acid content of the sediments.

Scrobicularia contributes its own sterols to the faeces, especially cholesterol. Such contributions aredependent on the dietary sterols present. With a cholesterol-poor diet (herbivory), A5 4–desmethyl sterols are contributed to the faeces and dietary A8(14) sterols decrease, suggesting a A8(14) U021e2; A5 conversion may occur. With a cholesterol-rich diet (coprophagy), the A5 sterol is taken up from the diet.

Soleid eggs caught in the plankton off Algiers were reared and identified. Thus, the egg and the yolk sac stages of Microchirus ocellatus (L.) and M. azevia (Capello) were described, compared and differentiated from the corresponding stages of M. variegatus (Donovan). For the latter species, a large perivitelline space was often discernible.

In 1889, Cunningham referred some pelagic eggs caught near Eddystone (English Channel) to Solea variegata, owing to their similarity to the mature ovarian eggs of this species. Moreover, he considered the embryonic and larval stages described, illustrated and named ’species no. 1'by Raffaele (1888) as belonging to the same soleid. In further works, Cunningham studied the two-day-old larva (1890) and the newly hatched larva (1896). These papers and some others relating to Microchirus variegatus (Donovan, 1808) (present name of S. variegata) were reviewed by Ehrenbaum (1905), Padoa (1956), Nichols (1976) and Russell (1976).

Such eggs are often collected in the plankton of the Bay of Algiers, but I noted a great variability in their features. According to Quero et al.

A literature review and new data are used to clarify geographical patterns of community response to release from heavy grazing by green sea urchins, Strongylocentrotus droebachiensis (O.F. Müller) within the north-west Atlantic region. Large geographical areas identified where urchin-removal experiments have not been conducted are the Passamaquoddy Bay area of the northern Bay of Fundy, the south and west coasts of Newfoundland, and southern Labrador. Within the north-west Atlantic region, there has been variation in the degree of domination by Laminaria species of post-urchin-removal communities. This is probably due, at least in part, to variation in the availability of Laminaria populations in refugia from urchin grazing. The following hypothesis is developed and given a preliminary test: in eastern Newfoundland, the absence of refugial Laminaria longicruris populations is due to periodic ice-scour. Despite the absence of significant Laminaria populations following short-term (<5 years) urchin-removal experiments in some areas, it is suggested that Laminaria spp. may be the natural, long-term community dominants in the absence of significant urchin grazing throughout the region. In view of the logistic problems involved in conducting long-term (6–15 years) urchin-removal experiments, it is suggested that urchin-removal/Laminaria-seeding experiments should be conducted within this region.

Development, growth, and survival data derived from laboratory experiments are provided for Lepeophtheirus salmonis, a common ectoparasite of wild and sea-farmed salmonids. The mean development time of eggs was 419·1 hours (17·5 days) at 5°C, 207·1 hours (8·6 days) at 10°C, and 130·8 hours (5·5 days) at 15°C. Development from the first nauplius to the infectious copepodid stage took 222·3 hours (9·3 days) at 5°C, 87·4 hours (3·6 days) at 10°C, and 44·8 (1·9 days) hours at 15°C. Development from the egg to the adult male took 40 days, and from the egg to the adult female 52 days at 10°C. No egg development occurred at 10‰ salinity. At 15‰ eggs developed but failed to produce active nauplii. At higher salinities (20–3‰) active nauplii were produced, but copepodids were only obtained at 30‰. Copepodids survived for less than 1 day in waters with a salinity of 10‰ or less. At higher salinities (15–30‰) and temperatures of 5,10, and 15°C average survival times ranged between 2 and 8 days.