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.

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.

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.

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.

Immersed shannies (Blennius pholis) showed peak locomotory activity coincident with daylight high tides. Emersion caused cessation of breathing and bradycardia though Q02 was little affected. Q02 fell, however, when the abdomen was enclosed in an impermeable sheath to block cutaneous respiration. Gulping of air into the extensively vascular oesophagus probably also acts as a means of aerial respiration. Reimmersion of fish caused a transient bradycardia followed by a tachycardia and a fall in Q02 followed subsequently by a rise. The results are discussed in relation to the behavioural, circulatory, respiratory and morphological adaptations of the shanny to the intertidal habitat.

A cytochrome P-450-dependent benzo[a]pyrene mono-oxygenase enzyme system (BPM) has been identified and partially characterized in males of the shore crab Carcinus maenas (L.). Apparent Km values obtained at 30 °C using microsomal preparations from the antennary glands of animals collected during summer were in the range 1.61–2.11 µM. The cytochrome P-450 content was 0·022 nmol/mg microsomal protein when BPM activity in the same preparation was 0·085 nmol/mg protein/min.

Laboratory experiments to determine the stage durations of Pseudocalanus elongatus (Boeck) and Calanus sp. have been described. The duration of all the nauplius and copepodid stages at temperatures ranging from 4° to 15 CC is given for both species. The effect of temperature on the development rate of copepod eggs has also been determined at these temperatures. The effects of food supply and temperature on the distribution, abundance and development rate of different species of copepods are discussed.

Measurements of pH, oxygen content, O2-combining capacity, and haemoglobin concentration were made for the vascular blood of the burrowing polychaete Neoamphitrite figulus in order to assess the role of its two respiratory pigments in respiration. The oxygen equilibrium curve of the erythrocruorin (extracellular haemoglobin) in the vessels was sigmoidal, having an n50 value of 1·5 and a low affinity for oxygen as determined by the P50 which was 26 mmHg at pH 7·31 and 18 °C. O2-binding by the erythrocruorin is sensitive to changes in pH (Δ log P50/Δ log pH = –0·24 to –0·29). The coelomic cell haemoglobin has a hyperbolic equilibrium curve (n50 = 1·0) and a high affinity for oxygen (P50 = 4·5 mmHg) independent of pH, suggesting an oxygen transfer system from the erythrocruorin to the coelomic cells.

Fertilizations of Magelona filiformis, M. alleni, and M. mirabilis were made in the laboratory and the resulting larvae reared through the earliest stages. Later stages of all three species were obtained from the plankton and induced to metamorphose in the laboratory. The long larval tentacles derive from the prototroch and associated tissues. Adult tentacles appear during later pelagic life as thickenings at the bases of the larval tentacles; the latter, together with the long provisional bristles, are discarded at metamorphosis. The early larvae of M. alleni are considerably larger than equivalent stages of the other two species. The early larvae of M. mirabilis are peculiar in that at first the larval tentacle of the left side is a mere stump while that of the right side is relatively large; in the other two species both tentacles are of equal length. Larvae of the three species are readily identifiable by characters described in the text.

Chemostats were used to construct nutrient (vitamin B12) and energy budgets for the flagellate Monochrysis (Pavlova lutheri (Droop) Green) under varying conditions of nutrient and light limitation and luxury, the aim being to describe light limitation and luxury in terms analogous to those of the Cell Quota nutrient model. Measurements were made of steady-state dilution rate, biomass, cell quota, cell chlorophyll a, cell energy content, dark respiration and photosynthetic efficiency, under low irradiance (<13 W per m2).

Cell energy content was 0·54 joules per million cells and was not influenced by growth rate or nutrient/light status. Cell chlorophyll a was 25% less in the nutrient-limited cultures and did not show a clear trend with growth rate except in cultures receiving less than 4·3 W per m2. The effective specific extinction coefficient was 0·12 cm2 per μg chlorophyll. The photosynthesis/irradiance relation was linear. The mean slope (= efficiency) in samples from the light-limited chemostats was 0·225 and was independent of dilution rate. Samples from nutrient-limited chemostats showed a much lower slope, which decreased with decreasing dilution rate. These findings were confirmed by the chemostat kinetic data. Dark respiration varied with dilution rate in a hyperbolic manner and was greater in the nutrient- than the light-limited chemostat.

Light level had no effect on the subsistence quota when the nutrient was limiting, whereas under light-limiting conditions the subsistence quotas were enlarged in inverse proportion to the incident irradiance, thus showing a threshold rather than multiplicative interaction between light and the nutrient.

Energy absorption was very little reduced on nutrient limitation, the great reduction in overall efficiency being associated mainly with the reduction in photosynthetic efficiency.

The reciprocal of photosynthetic efficiency was shown to be analogous to a standardized nutrient cell quota, and an analogous coefficient of luxury could be defined as the ratio of the light-limited to nutrient-limited photosynthetic efficiency at the same growth rate. Thus, light limitation and luxury could be described in terms compatible with the nutrient model without having to introduce new concepts, and a practical criterion between light- and nutrient-limitation could be provided.

The planktonic foraminifer Globigerinoides sacculifer (Brady) was cultured under two different light intensities and in continuous darkness. High light intensity (HLI = 400–500 μeinsteins/m2/s) resulted in a longer lifespan, a greater number of chambers formed, and a larger final shell size compared with individuals cultured under low light intensity (LLI = 20–50 μeinsteins/m2/s) or in continuous darkness. Shell growth rates were unaffected by increasing light intensity, but gametogenesis was delayed. Continuous darkness induced a rapid onset of gametogenesis in organisms with shell lengths larger than 250 μm. Feeding frequency had a greater effect on growth and reproduction than light intensity under conditions of LLI and HLI, but continuous darkness had an overriding effect on growth and reproduction owing to the rapid onset of gametogenesis which terminated the life of the mother cell. Our previous data indicated that the longevity of G. sacculifer was dependent on feeding frequency, and that G. sacculifer cultured under LLI had a lifespan of approximately 2–4 weeks. Present results suggest that the lifespan can vary from a minimum of 8 days for organisms fed daily in continuous darkness to a maximum of 54 days for organisms fed once every 7 days and maintained in HLI. It is concluded that individual G. sacculifer attain a shell size greater than 600 μm only if they maintain their position in the euphotic zone. Prolonged existence below the euphotic zone would result in premature death or gametogenesis following stunted shell growth.

The life histories of Gracilaria verrucosa from England and from Vancouver Island, Canada, were completed in culture. Although representatives of the two populations were morphologically and anatomically indistinguishable, their chromosome numbers differed markedly, being n = 32 for British material and n = 24 for western Canadian plants. It is propounded that the Vancouver Island plants are not authentic G. verrucosa and, moreover, that this name may have been applied erroneously in other reports of the species from localities distant from the British Isles (type locality).

Variation in the abundance of Barleeia unifasciata is compared in several red algal species between June 1978 and June 1980 at Cooskeen Cove, Bantry Bay, Ireland. Population abundance in all algae varied seasonally, exhibiting a cycle of late-summer to autumn maxima, with winter to early summer minima. Greatest abundance was recorded in those algae which formed compact turf-like growths suitable for the entrapment of diatoms and detrital material and provided greatest shelter from wave-crash. Length frequency data showed the main recruitment period to be late June-October with a peak in August with juveniles present in all months of the year. Maximum life span was shown to be 2 years or more with only 15 % of the population surviving into the second year. Sexual development and reproductive cycle was determined for 0 + and 1 + animals. Mature males produced sperm continuously throughout the year. Not all 0 + females spawned in their first year. Summer spawning 0 + females exhibited reduced sexual activity in October and spawned again in the following summer. Some 1 + females spawned in winter and spring. Delayed sexual development in some individuals of both sexes was related to late hatching.

Freshly captured Nautilus macromphalus were observed to place new cameral liquid into emptied or partially emptied chambers, both at the surface and at 250 m, in response to sudden buoyancy increase. The sudden addition of buoyancy was accomplished either through removal of cameral liquid from chambers, removal of shell material from the apertural region of the body chamber, or by cementing buoyant corks on the sides of the shell. A maximal refilling rate of 100 μl/h was observed. The osmolality of refilled cameral liquid was observed to match closely the osmolality of the original cameral liquid. The refilling mechanism allows Nautilus to regain neutral buoyancy after sudden buoyancy gain, such as could be expected to occur from shell loss due to predatory attack on the Nautilus, or from shell breakage.

Elminius modestus cyprids settle readily in contact with adult barnacles in the field, and do not discriminate between conspecific and alien adults. This settlement strategy is contrasted with that previously shown to be employed by Balanus balanoides.