The tidal streams in the Channel Islands region are rotary anticlockwise. At spring tides anticlockwise Eulerian residual currents of about 20 cm s–1 develop around Guernsey which indicate that frictional effects exceed those due to the Earth's rotation in the generation of Eulerian residual currents in this shallow-water situation. Lagrangian anticlockwise residual currents can exceed 60 cm s–1 at spring tides, indicating that Stokes-induced currents are larger than the Eulerian residual currents around Guernsey. Remote sensing studies show anticlockwise-directed jets which also indicate an anti-clockwise circulation around the island. A tidal circulation pattern for the Channel Islands area is presented based on anticlockwise gyres around all the major topographic features in the region. This pattern off low is consistent with the formation of the well-known front between Guernsey and Jersey and the residual currents derived from a numerical model.

The paper describes the design and use of a tide machine capable of producing near-sinusoidal hydrostatic pressure cycles varying in period from 12 to 999 min and in amplitude from 0·4 to 3·2 m. In conjunction with infra-red detection units and a microprocessor logging system the apparatus can be used to detect and record the response of a variety of organisms to cyclic pressure changes.

In Britain, the cushion star Asterina gibbosa Pennant 1897 (Echinodermata, Asteroidea) is confined to the west coast, where it occurs on rocky shores, often sympatrically with the closely related Asterina phylactica Emson & Crump 1979 (Crump & Emson, 1983; Emson & Crump, 1984). The vertical distribution of A. gibbosa extends from about 100 m depth, into the intertidal; however, littoral cushion stars occupy rock pools and relatively damp habitats such as gulley walls, crevices, overhangs and the underside of boulders, generally on the lower shore (Emson, 1979). On shores with rock pools, cushion stars may extend their upper limits of vertical distribution but not beyond the mean high-water neap-tide level (Crump & Emson, 1978). Absence of A. gibbosa from higher shore levels has been related to intolerance to desiccation and high temperature, inadequate food supply, and complex behavioural responses to gravity and light (Crozier, 1935; Emson, 1979; Crump & Emson, 1983). Prior to the present study, it has not been possible to discuss the influence of respiratory requirements on the vertical distribution of this species.

The common dogfish (Scyliorhinus canicula L.) is caught regularly at Plymouth and is parasitized by two monogeneans, the gill-parasitic polyopisthocotylean Hexabothrium appendiculatum (Kuhn, 1829) Nordmann, 1832 and the skin-parasitic microbothriid Leptocotyle minor (Monticelli, 1888) Gallien, 1937. Unsuccessful attempts have been made to hatch the larvae of both of these parasites, e.g. Euzet (1957) and Wiskin (1970) for H. appendiculatum, and Llewellyn (1963) and Kearn (1965) for L. minor. Euzet (1957) and Kearn (1965) found that larvae developed within the eggs of H. appendiculatum and L. minor respectively but that these larvae failed to hatch.

Previous studies of the anatomy of the oncomiracidia of the hexabothriids Rajonchocotyle emarginata and Hexabothrium appendiculatum have been made on unhatched larvae viewed through the egg shell or on larvae pushed out of the egg by coverslip pressure. A study of freshly hatched, free-swimming oncomiracidia has permitted a more detailed anatomical study especially of the gland cell system, the distribution of locomotory ciliated cells and surface sensilla and the flame cell system. Anatomically, the two larvae are closely similar but the oncomiracidium of R. emarginata possesses spherical refringent droplets in the locomotory ciliated cells and, in the head region, a pair of translucent bodies which may be photoreceptors. The oncomiracidia of both parasites possess posterior body gland cells with ducts entering the haptor. Such gland cells have not been recorded previously in the larvae of hexabothriids or in those of other polyopisthocotyleans and the function of these and other gland cells is discussed.

The gill-parasitic polyopisthocotylean monogenean, Hexabothrium appendiculatum and the skin-parasitic microbothriid monogenean, Leptocotyle minor share the same host, the common dogfish Scyliorhinus canicula. The larvae of these parasites are stimulated to hatch by host skin secretions and the behaviour patterns of these larvae have been found to be remarkably similar. The freshly hatched oncomiracidia of both parasites rarely remain swimming (in the presence of hatching stimulants) for more than 30 min; there is a strong tendency for the larvae to attach themselves temporarily or permanently by either the anterior or posterior ends to glass or Perspex surfaces. Other important features of the behaviour of these oncomiracidia are their erratic mode of swimming and their apparent lack of response to environmental stimuli such as light, shadows, mechanical disturbance or water currents. There is some evidence that the swimming oncomiracidia of both parasites may be negatively geotactic after hatching but this response is weak and of short duration. The erratic swimming pattern, the lack of response to environmental factors and the readiness to attach to available surfaces seem likely to be particularly favourable for the establishment of larvae on the surfaces of dogfishes foraging at the sea bottom and providing the hatching stimulus for drifting eggs.

Activity patterns of the first maxillae of Calanus helgolandicus and Temora longicornis, restrained in a flow-through system, were investigated using a micro-impedance electrode technique. Copepods were exposed to four dinoflagellate species of similar cell size with filtered sea water and the diatom Thalassiosira weissfloggi as controls. In short-term transition experiments the beat frequency of the maxilla changed rapidly with the introduction and removal of cells from the surrounding medium. Similarly the introduction of cell-free algal homogenate, filtered through a 0·2 µm membrane, produced elevated beat frequencies, evidence consistent with chemosensory food detection. During 24 h exposure experiments frequencies for Calanus on all dinoflagellate diets were lower than for the diatom, and in the case of Scrippsiella trochoidea did not differ significantly from the seawater controls. In Temora, frequencies when feeding on dinoflagellates, except Prorocentrum micans, were lower than on the diatom. With Scrippsiella trochoidea and Gonyaulax tamarensis beat frequencies were the same as those for the sea-water controls. Significant depression of frequency below that observed in filtered sea water was shown for both copepods when presented with the bloom-forming, Gyrodinium aureolum. Differences in beat frequency in response to dinoflagellate diets are mirrored by other aspects of feeding activity, gut contents, egg production and mortality.

Within the hepatopancreas of the shrimp Penaeus semisulcatus the functional develop ment and subsequent decay of M-‘midget’ cells is described and linked with the moult cycle. During the feeding stages the frequency of M-cells increases and they each form a large dense vacuole which contains proteinaceous material. Precursors for this material are probably derived from the haemolymph as the cells have no direct contact with the lumen of the gland. During the non-feeding stages before and after ecdysis the contents of the vacuole are progressively removed, probably to the haemolymph. Finally the cells die before the animals recommence feeding.

Stage-2 nauplii larvae were taken in near-surface inshore tow-nets on the Northumberland coast in January and February of 1986, confirming isolated reports of similar observations in 1979–80. These occurrences are much earlier than expected from the normally described progression of naupliar release in British waters. It is suggested that premature larval release may be occasioned by damage to, or predation on, parent colonies.

Gross activity recordings from the recurrent facial nerve were made in unrestrained specimens of Gaidropsarus and Ciliata by means of implanted silver-wire electrodes. Responses to tactile stimuli could be evoked almost anywhere on the skin. Application of the contents of the urinary bladders of other rocklings, water in which other rocklings were kept, and (diluted) human saliva to the anterior dorsal fin evoked strong responses. Responses to more elementary chemical stimuli like amino acids, salts, aldehydes, and acids, were much weaker or absent. The results favour a special chemoreceptive function of the vibratile anterior dorsal fin.

A 5-year study of the population biology of the common shrimp Crangon crangon (L.) in the Bristol Channel is reported. Samples were collected from three commercial fishermen and from the filter screens of five power stations taking water from the estuary.

The Severn Estuary and Bristol Channel were found to contain a single shrimp population which undertook regular seasonal migrations in order to avoid low salinities and to reproduce. Previous studies had assumed that the regions held separate populations which migrated to avoid low winter temperatures.

Comparisons of the behaviour of herring (Clupea harengus L.) were made in the light and dark by means of an infra-red sensitive TV system and video recording. Herring which were schooling in the light became less active in the dark, their swimming speed decreased, they tended to disperse and the proportion of gliding compared with swimming fish increased. Herring which were not schooling in the light increased their swimming speed in the dark.

When subjected to transient sound stimuli herring made fast-startle responses. The proportion of fish responding was lower in the dark. The directionality of the response (the proportion turning away from the sound source) was the same in the light and dark suggesting there was no visual component in the response.

The proportion of swimming and gliding fish affected both response rate and directionality. Gliding fish tended to have a higher response rate and better directionality than swimming fish, although this depended on the conditions of the experiment. The configuration of the body of swimming fish at the onset of a transient sound stimulus was important. Of the swimming fish, over 80% of the responders turned away from the direction in which the tip of the caudal fin was pointing at the onset of the stimulus. Gliding fish are in a better ‘neutral’ posture to initiate a startle response and to turn away from the sound source.

Comparisons of awareness (sensory thresholds) in the light and dark using startle responses are complicated by differences in the numbers of gliding and swimming fish.