Rainbow trout were exposed to five different concentrations of a unialgal culture of Gyrodinium aureolum in laboratory tanks. All the concentrations used proved lethal within 24 h. The gills of the dead fish showed no mechanical occlusion by the algae but all displayed marked histological changes characterized by necrotic degeneration and disintegration of the lamellar epithelium.

Reproductive cycles are described for subtidal and intertidal populations of the, starfish Asterias rubens L. and for a subtidal population of the starfish Marthasterias glacialis L. on the south-west coast of Britain. Intertidal A. rubens had a clearly defined reproductive cycle with spring-early summer spawning. Pyloric caecum indices were inversely related to gonad indices. Subtidal A. rubens had lower gonad indices and less seasonal variation in the pyloric caecum indices. Gonad indices of M. glacialis suggest few animals in the population studied were breeding, but it is likely that this species also spawns in summer.

Plankton samples and larval rearing studies suggest a planktotrophic pelagic life of approximately 90 days for A. rubens. Field observations and laboratory experiments show larvae settle on a wide range of substrata. Recruitment to an intertidal population of A. rubens at Hollicombe Reef occurred in July 1980 and September 1981. Growth of juvenile starfish was followed for 17 months. Juvenile starfish feed carnivorously at the completion of metamorphosis. Early growth is rapid; however, there is a reduction in the growth rate during winter months. Feeding and growth of juvenile A. rubens is compared with published data on juvenile starfish of other species.

During a routine North Sea demersal fish survey, very low fish catches were recorded at two primary stations off the Danish coast in September 1981. The catch of benthos at thesestations was much greater than the previous year, and underwater photographs from a headline camera revealed that this was a result of most infaunal species having emerged from beneath the sand. The phenomenon was assumed to be caused by low oxygen concentrations in bottom water following the collapse of a bloom of the dinoflagellate Ceratium furca.

Nucella lapillus and Littorina littorea afford examples of turbinately coiled shells with no space between the columella and the inner face of the whorls. Three constants are sufficient to determine the form of such shells: λ, the ratio between diameters of successive whorls; β, the semi-apical angle and ρ, the ratio of aperture length and breadth in the apertural plane passing through the axis. The variation of these three constants with size was examined and shown to be relatively small and insignificant in Nucella, but in Littorina it was significant.

For Nucella and Littorina these shell characteristics were used to relate for the nth whorl, the length along the shell spiral (ln) to the shell height (Hn), the latter being the measure usually employed in growth studies. This relation was derived mathematically and confirmed empirically as

where α is the angle of the logarithmic spiral given by α = tan−1 2π sin β/loge λ. The increased resolution of the micro-growth band increments, which are measured along the shell spiral was directly related to the ln:Hn ratios.

Since the formula for the ln/Hn ratio (= shell conversion factor) includes λ, β and ρ, the three constants necessary to determine shell form in turbinately coiled shells of the type described, the shell conversion factor may be a better index of shell shape than indices based on a single constant. In species where the shell grows isometrically this ratio will remain constant, whereas changes in shell shape with size will influence this ratio. Such changes in shell shape during growth can be quantified in terms of the shell constants and when included in calculating the shell conversion factor, will show the relative magnitude of shell shape changes brought about by growth. The shell conversion factor may also be used to study the effects of ecological variations on the geometry of the shell.

The conical shell of the limpet, Patella vulgata, is geometrically a much simpler system in which direct shell measurements were used to relate length along the direction of maximum growth to the antero-posterior diameter of aperture.

The spread of the immigrant brown alga Sargassum muticum ( Yendo) Fensholt, within European waters is chronicled from 1973–1981. New populations of the attached alga are listed together with maps indicating the annual addition of sites. No populations of the alga were known beyond the bounds of the Solent region, southern Britain, until after 1975.

The age of the original Sargassum population found at Bembridge in 1973, and the discovery of drifting S. muticum in 1971, seems to date the initial introduction of the alga in the Channel as possibly the late 1960s.

This paper presents the establishment of Sargassum muticum as a permanent addition to the European marine flora. It is hoped that its future spread will continue to be documented, providing useful information upon the invasion strategy of an ‘aggressive’ introduced marine species.

The shape of such morphological characters as leaves and air vesicles of the introduced brown alga Sargassum muticum (Yendo) Fensholt were found to vary seasonally. A range of observations is presented together with a general description of European material.

Seasonal variations in the range of air vesicle and leaf shape upon the brown alga Sargassum muticum (Yendo) Fensholt provide some discrepancies with descriptions of material from the alga's indigenous Japanese and introduced British Columbian habitats.

Experimental observations indicate that mucronate air vesicles are most common at low (i.e. 10 °C) and high (i.e. 25 °C) temperatures, with those of 30 °C being injurious to plant growth. Air vesicles with spiked proliferations are also seen to increase in occurrence with an increasing light intensity at 20 °C. Excised ‘winter’ form leaves collected in February were able to regenerate ‘summer’ form leaves from their damaged bases, under culture conditions.

Field and laboratory investigations show that leaf and air vesicle shape tend to vary seasonally and may be experimentally changed by both temperature and light intensity. Such plasticity observed in the morphology of these characters in S. muticum raises doubts as to the taxonomic status of many species ascribed to the large genus Sargassum.

The endogenous activity rhythm of the estuarine amphipod Corophium volutator has been studied by direct observation and with the use of time lapse photography. The rhythm persists under constant conditions having a free running period of between 12 and 13 h, and with activity maxima occurring during the early ebb. Freshly collected animals show a rhythm which is modulated on a semi-lunar basis, the activity maxima being attenuated during the neap tide periods, and the rhythm has also been found to vary in definition throughout the year. The activity pattern is most clearly denned in early summer and autumn, the population becoming arrhythmic during the winter months. The rhythm is relatively unaffected by the ambient light intensity and temperature of the recording conditions, and is evident in all post-natal stages of development. The possibility of mutual entrainment is discussed.

The endogenous rhythm of swimming activity shown by Corophium is reset by pulses of sub-zero temperature, the activity maxima being rephased to the time of rewarming at the end of the cold period. Chilling is not equally effective at all stages of the tide, pulses applied during the flood tide causing a phase delay, while those applied during the ebb advance the rhythm. Chilling at the time of low water induces arrhythmic swimming and it is suggested that the rhythm enters a state of equivocation at this time when an advance and a delay in phase are both equally probable. This results in the loss of synchronization between individuals and the disappearance of the overt rhythm from the sample population.

The tidal rhythm of swimming activity shown by the estuarine amphipod Corophium volutator can be entrained to cycles of temperature and immersion in the laboratory. The rhythm is phased to the period of increasing temperature, or to the time at which the animals are wetted by the artificial tide, and the activity maxima follow the Zeitgeber with a phase delay of about 5–6 h in each case. Entrainment to these variables alone is inadequate to account for ebb tide swimming in the natural state, and it is likely that the rhythm is normally entrained by a number of factors of variable significance.

The movements, abundance, age composition and growth of bass, Dicentrarchus labrax (L.), in the Severn Estuary and inner Bristol Channel have been described from regular samples offish taken from power-station intake screens between 1972 and 1977. Bass began to move into the estuary during late August or September and reached peak abundance between September and early November. The tendency for fish to move seawards in the late autumn and winter may be related to declining water temperatures in the estuary. Likewise, differences in abundance between years appear to be related to annual differences in temperature. Although the populations were dominated by the 0 + age class, successively decreasing numbers of the next four age classes and occasional 5 + fish were also present. Respective mean standard lengths of bass in the estuary at the end of their first to fifth years of life were approximately 65 mm (≡ 4·5 g), 130 mm (≡ 37·9 g), 190 mm (≡ 121·1 g), 250 mm (≡ 280·4 g) and 290 mm (≡ 441.5 g). Growth occurred predominantly between May and September, with the mean standard length of 1 + fish increasing from approximately 65 mm (≡ 4·5 g) to 130 mm (≡ 37·9 g).

Spinal cords in deep sea fishes of 37 families have been examined for the presence and relative size of Mauthner axons. No correlation has been found between fish size, and the relative diameter of the Mauthner axon in different species. However, counts of primary motoneuron number and myotomal muscle fibre number in each segment suggest that Mauthner axon diameter is related to the numbers of these in each segment. The behavioural role of the Mauthner system is discussed, and it is concluded that in certain elongate-bodied fishes such as halosaurs and macrourids, a C-type startle response is unlikely.

Rapid fixing of skeletal muscle by a ‘freeze-clamp’ technique results in up to a 3-fold lower lactate, a slightly higher pyruvate concentration and a 2- to 4-fold decrease in lactate/pyruvate ratio, to the lowest value yet recorded for fish muscle, when compared with the more usual method of direct immersion in liquid nitrogen. This is attributed to the faster cooling rate of freeze-clamped muscle minimizing ‘sampling anoxia’. Immobilizing fish either by anaesthetic or stunning produces no significant change in metabolite levels. It is concluded that it is relatively easy to handle quiescent flatfish, but light anaesthesia ensures no muscular activity.

Body scales in dinoflagellate species belonging to Heterocapsa developed in vesicles derived from the Golgi apparatus, but did not appear within the stacked Golgi cisternae. The membranes of the scale vesicles functioned as molds for the developing scales. Mature scales within expanded vesicles moved to the flagellar area, the site of release. Body scales were seen within the cytoplasm of Heterocapsa spp. fixed at various times in the light: dark cycle, suggesting that scales are formed and probably released continuously.

Atrispinum labracis (Van Beneden & Hesse) n.comb. syn. Microcotyle labracis Van Beneden & Hesse, 1863, parasitizes the bass Dicentrarchus labrax but almost only in the open sea; the very low prevalence of parasites on juvenile estuarine hosts was not due to intolerance of lower salinities in this habitat. The intensity of infection on open-sea bass was rarely more than 2 per fish but the strict localization of the habitat to the outer hemibranch of the ventral end of the first gill arch is thought to enhance the mating opportunities. The parasite attaches itself asymmetrically to the gill by a permanent morphological inclination of the body with respect to the haptor which is itself symmetrically aligned on a single primary lamella.

Substantial differences between the copulatory apparatus of A. labracis and that of Microcotyle donavini Van Beneden & Hesse, 1863, the type of Microcotyle, have made necessary the transfer of the parasite from Dicentrarchus labrax to Atrispinum Maillard & Noisy, 1979 and a consequent amendment to the diagnosis of the subfamily Atriasterinae Maillard & Noisy, 1979.

The teeth and grasping spines of Sagitta are similar in structure, both having a central pulp cavity surrounded by two electron-dense chitinous layers. The cells of the pulp cavity contain microtubules arranged along the long axis. The two chitinous tubes are separated by a less-dense zone crossed by coarse fibrils linking the two. The teeth and spines insert into less electron-dense chitin (presumably flexible) and are moved by processes of anchor cells which pass into the basal chitinous zone. The inner region of the anchor cells is apposed to the connective tissue layer on to which the muscles of the teeth and spines insert. At the base of the pulp cavity, i.e. at the secretory zone where the teeth and spines are formed, the cells of the pulp cavity contain electron-dense granules in which zinc is found; zinc is also present in the inner and outer dense chitin layers at high concentration (0·5–1·0% of the dry wt).

Both spines and teeth are tipped with fibrous cones containing silicon. It is suggested that the zinc associated with the chitin serves to toughen the teeth and spines and render them less liable to fracture, and that the silicon in the tips confers hardness to this vulnerable region.