Samples of the squid Loligo forbesi Steenstrup 1856 were obtained from commercial catches and research cruises in the Irish and Celtic Seas from August 1991 until October 1993. Age and growth of L. forbesi were estimated from putative daily statolith growth increment counts and from length-frequency data. Indirect evidence of the daily deposition of growth increments was obtained by counting increments on statoliths from immature female squid from successive monthly modes, during a four-month period when length-frequency growth estimates were high. Female growth estimates from length-frequency analysis (15–30 mm per month) were slightly lower than statolith-based estimates (30 mm per month). Statolith data indicated that both sexes had a life-span of approximately one year and that males grew faster and attained a larger size than females. In both sexes growth was found to be logarithmic over the size range sampled (28–505 mm mantle length). Mean estimated age of mature males and females was 317 and 312 days respectively, with the minimum age at maturity found to be 236 and 241 days. Back-calculations of hatching dates showed an extended spawning season from November to May. Squid hatched in the spring grew faster than those hatched in the autumn and winter. In post-recruit L. forbesi, growth of head, mantle and viscera were approximately isometric with body mass. The digestive gland showed slight positive allometry, whilst reproductive organs showed strong positive allometry.

An extensive study of an intertidal population of Nephtys caeca Fabricius (Annelida: Polychaeta) was conducted from 1986 to 1988 in I'Anse-à-l'Orignal on the southern shore of the lower St Lawrence Estuary. The sampling, carried out at three levels in the intertidal zone, was designed to study spatio-temporal variations in oocyte diameter (1988), age (1986), density (1986–1987) and individual body weight (1986–1987). The highest oocyte diameters were found in early May when breeding occurred. A relatively long period (from 20 June to 23 August), when oocytes were not visible with a binocular microscope, was also observed. Oocyte maturation began in late summer / early autumn. Settlement did not seem to take place in the intertidal zone, suggesting sublittoral larval recruitment. Peak densities occurred at the intermediate tidal level only in June. Nephtys caeca density varied significantly according to tidal levels, but only in 1987. The number of larger individuals (>320 mg in partial weight) increased markedly with decreasing level on the shore. At the lower tidal level a significant temporal variation in body weight was observed, while mean weight reached its maximum value in July or August 1986. Body weight later decreased progressively (July-November). In June and July 1986 arrivals of juveniles were seen to be greater at every level than during 1987. Six growth-rings were found in the pharyngeal jaws of the individuals in this intertidal population (November 1986). The decomposition of the polymodal weight-frequency distributions of individuals >75 or >85 mg in partial weight isolated four or five size-groups (MacDonald & Pitcher, 1979).

Densities and growth rates of Ensis directus (Bivalvia: Solenidae), a recent invader of the Wadden Sea, were monitored at 15 stations (12 transects and 3 squares) covering a wide range of intertidal levels and sediment types on Balgzand, a tidal-flat area in the western-most part of the Wadden Sea, during 1982–1994. In this period, recruitment was weak in all but one year (1991). Settlement took place in summer over a wide range of intertidal levels, but high survival of recruits was limited to stations below the level of mean low tides. Growth rates were also maximal at these low intertidal levels. In such areas they reached a mean length of about 6 cm in the first winter, about 12 cm in the second, and about 14 cm in the third winter. These growth rates were high compared with published records from other intertidal and shallow subtidal areas.

Relatively exposed parts of the lower intertidal zone, characterized by clean sands and infrequent emersion, are a poorly occupied habitat of the Wadden Sea and offer an available niche to a new species that is well adapted to such harsh environmental conditions. In such areas, E. directus has become a dominant member of the benthos and in 1992 and 1993 reached high biomass and production values of >10 g AFDW m−2.

The orientation of tail-flip escape swimming in a range of adult decapod and mysid crustaceans is reviewed. In mechanical terms, tail-flip swimming constitutes unsteady locomotion in which a single ‘appendage’, the abdomen, produces thrust by a combination of a rowing action and a final ‘squeeze’ force when the abdomen presses against the cephalothorax. In small crustaceans, a symmetrical ‘jack-knife’ tail-flip is more typical. Tail-flip flexion is controlled by two giant-fibre pathways, and also by a non-giant-neuronal network. The direction of thrust in the sagittal plane, and hence the elevation, translation and rotation of the tail-flip are dependent upon the point of stimulation and on the giant-fibre pathway activated. The laterality of the stimulus also affects the orientation of swimming, which is directed away from the point of stimulation. In large decapods such as the lobsters Nephrops norvegicus and Jasus lalandii steering is produced by asym-metrical movements of various abdominal appendages, and by rotation of the abdomen about the cephalothorax. In slipper lobsters the flattened antennae provide steering surfaces. In smaller decapods, such as the brown shrimp Crangon crangon, and in mysids, such as Praunus flexuosus, steering is effected by a rapid rotation of the whole body about its longitudinal axis during the initial stages of tail-flip flexion. The effectiveness of tail-flip swimming is considered in the context of predator-prey interactions under natural conditions and in relation to artificial threats from fishing gear.

The reproductive strategies of male and female Loligo forbesi Steenstrup, 1856 were investigated from samples obtained from commercial catches and research cruises in Irish waters. In females maturity increased with size, but in males two modes in the size at maturity were identified, with approximately 40% mature at small size (180–200 mm mantle length), and the remainder mature at >250 mm mantle length. The difference in estimated age of the two modes of mature males was small, so size differences were probably due to different growth rates. Growth and maturation proceeded together in both sexes over much of the life-cycle. The effect of maturation on relative growth of somatic tissues was examined using analysis of covariance and multivariate regressions. In males there was a significant decline in total mass, and in mass of mantle, head and viscera, relative to mantle length with maturation. In females total mass was not significantly affected by maturation, but relative masses of head, mantle and viscera declined with maturation, indicating that energy was diverted from somatic growth to gonad production. Potential fecundity estimates were obtained by counting eggs and ova in the oviduct and ovary of mature females and were in the range 2500 to 10,500 (mean 5800). Fecundity was positively related to mantle length. The ovaries of mature females contained a range of egg sizes and developmental stages, indicating that spawning probably occurs intermittently.

Morphological and genetic evidence is presented which supports the existence of periostracal adventitious hairs on spat of the mussel Mytilus edulis. This character appears not to have been reported previously for Mytilus, and was thought to be restricted to a closely-related genus, Modiolus. The species identity of hairy mussel spat was confirmed by PCR (polymerase chain reaction) amplification of a diagnostic portion of the nuclear ribosomal DNA repeat unit (i.e. the ITS-2 region). Size-frequency analysis of spat, sampled in mid-September 1993, from rock pools and from the byssus of a nearby adult mussel bed, showed that hairy spat (mean shell length 1.87 mm, SE 0.17) were significantly (t=7.74; P<0·001) smaller than smooth-shelled spat (mean shell length 2.77 mm, SE 0.28), although not all small-sized individuals displayed this character. These findings suggest that there is a gradual loss of hairs (through abrasion or by ‘programmed’ loss) as the animal grows. We suggest that this character has some adaptive significance since it probably reduces predation by boring gastropods (e.g. juvenile Nucella lapillus) and may inhibit fouling, particularly by conspecifics, during the primary settlement phase.

The digestive gland of the tropical sepioid Idiosepius pygmaeus (Steenstrup) (Cephalopoda: Idiosepiidae) is characterized by a single cell type which secretes proteinaceous spherical bodies, the secretory spheres. Changes in the structure of the gland with feeding were investigated through a field sampling programme and a laboratory feeding experiment. Specimens were collected in the field on three consecutive days. There was a significant increase in the number of spheres during the day. A laboratory-based night trial showed that numbers of secretory spheres remained high during the night. After feeding there was a rapid and marked increase in the number of secretory spheres, suggesting that upon registering a stimulus the digestive gland secretes large amounts of enzymes. The process is rapid with an increase in the number of spheres occurred one hour after feeding. A second peak occurred 16 hours after feeding, suggesting that there may be two phases to the digestive cycle. This study examined natural and experimental patterns in the digestive gland and estimated the time involved in the digestive activity of I. pygmaeus.

INTRODUCTION

The problems of observing the behaviour of mid-water animals are considerable. The depths involved are generally too great to allow free diving, and because the population density is low, useful observations from submersibles and remote cameras are rare. Animals brought to the surface are often in too poor a condition to behave at all normally. The hyperiid amphipods are one of the best groups to work with in trying to overcome these difficulties. They are relatively common and frequently observed from submersibles, where they congregate round the lights. They are tough, survive capture and behave well in aquaria at the surface (Land, 1992a). Compared with other groups, a reasonable amount is known about their habits, especially their associations with gelatinous animals on which they prey or have commensal relationships (Harbison et al., 1977; Madin & Harbison, 1977; Diebel, 1988). It is also known that they sometimes form swarms (Lobel & Randall, 1986).

This investigation of the diet of 801 corkwing wrasse (Crenilabrus melops: Teleostei; Labridae) from Galway Bay and a sample of 51 corkwings from Dinard has shown that this species is primarily a carnivorous feeder, taking a varied diet with molluscs and crustaceans predominating. A gradual, size-related dietary shift was apparent, crustacean food being favoured by the younger, smaller fish and molluscan food by older, larger fish. A decrease in niche breadth indicated an increase in dietary specialization with increasing length. Little seasonal variation was observed in the consumption of the major food categories. Feeding intensity, however, was influenced by the sea-water temperature. Non-feeding fish were recorded only between November and March in Galway Bay, and approximately two-thirds of the population examined in February had empty guts. Feeding intensity of males was significantly lower than that of females during the breeding season.

INTRODUCTION

The genus Illex is likely to constitute a large portion of the annual world ommastrephid squid catches (Roper et al, 1984), even though specific official statistics are difficult to obtain. The broad-tail short-fin squid Illex coindetii is a widespread species ranging from the western to the eastern Atlantic (Roper et al., 1984) and east through the whole Mediterranean Sea (Mangold & Boletzky, 1987). Usually a by-catch of important fisheries, it is caught mainly by trawlers. Although its economic value is lower than that of other squid species (i.e. Loligo spp.), in the Sicilian Channel Illex coindetii may represent a valuable resource due to its abundance.

In Italian waters, the available statistics (Cingolani et al., 1986) report that 2680 tonnes of ommastrephid squid were landed in 1982 (0.5% of the total landed catch). The main component of these was landed in Sicily (2183 tonnes), a consistently large part of which was no doubt Illex coindetii (Ragonese & Jereb, 1992). The catches came mainly from southern Sicilian waters (Sicilian Channel) where one of the major Mediterranean landing places is in Mazara del Vallo. Large trawlers (up to 200 gross tonnage) usually carry out long fishing trips (15–20 d), and Illex coindetii is caught mainly by those targeting Parapenaeus longirostris and Merluccius merluccius (Jereb & Ragonese, 1991).

This brief review describes the sense organs involved in orientation by cephalopods with a view to providing a basis for understanding the mechanisms involved. As in many other animals, vision is probably the most important sense involved in orientation. Cephalopods have paired eyes, sometimes providing binocular vision, and generally similar to those of many vertebrates in terms of their gross structure and performance. The main feature apparently lacking in most cephalopods is colour vision, although many have polarized vision. The second most important sense in cephalopods is the sense of balance provided by the statocysts. These paired organs, are functionally similar to the vertebrate vestibular system, and detect both linear and angular accelerations, giving the animal information on its spatial orientation and rotational movements. The statocysts may also be involved in hearing, for there is no doubt that they can detect some vibrations carried in the water and ground. The recently discovered cephalopod lateral line system also detects water-borne vibrations, but this is more probably used for locating other animals in low light conditions. Behavioural experiments have shown that olfaction is also important in cephalopod orientation, but, although there is good morphological data on the structures involved in olfaction, there are little supporting physiological data. Of the remaining senses used in orientation, touch is important for bottom living species, but less so for the free swimming animals. There is no evidence, so far, for electroreception or magnetic sensitivity in cephalopods.

Within the interstitial Cnidaria, the Hydrozoa dominate, with ten mesopsammic genera (living in the interstitial water of sandy bottoms), while the Anthozoa and Scyphozoa are represented by one genus each (Clausen & Salvini-Plawen, 1986; Bouillon & Grohmann, 1990). The only mesopsammic scyphozoans described so far are the small solitary polyps of the genus Stylocoronella, which is represented by two species, S. riedli (Salvini-Plawen, 1966) and S. variabilis (Salvini-Plawen, 1987). Little information is available on reproduction and nothing is known about the life-cycle of these interstitial scyphopolyps. By establishing a culture of the two Stylocoronella species, their development into undescribed stauromedusae could be observed for the first time

This article is a comparison and a synthesis of laboratory and field studies focused on the influence of larval and early juvenile behaviour on the recruitment mechanisms of sole in the northern part of the Bay of Biscay. Laboratory studies concerned the individual behaviour of larvae and juveniles, in particular, changes in swimming activity controlled by endogenous factors and also reactions to light, current, pressure and feeding conditions. Experiments were performed in different types of tanks fitted with special devices to vary light, pressure and current. Specific methods using visual observations and an infra-red converter as well as actographic techniques with infra-red barriers were utilized. The relative contribution of endogenous and external factors on swimming activity and orientation vary during ontogenesis. Field studies concern a time series of fine-scale vertical distribution of larval stages. Endogenous rhythms and light seem to play an important role in the control of diel vertical migration from early larval stages, whereas semi-diurnal and tidal behaviour could develop mainly after metamorphosis. A simulation is used for the study of the interactions between individual behaviour and tidal currents. Based on laboratory and field observations we propose and discuss a hypothesis of transport and migration. In the Bay of Biscay, such a hypothesis involves diffusion processes enhanced by active behaviour.

A cytological study was carried out on the main cells of the optic gland of male and female Sepia officinalis L. during sexual maturation (animals collected in the field). The results were correlated with experimental data on the mitogenic action of optic gland extracts collected during a period of secretory activity.

The main cells of the optic gland show some of the features of protein-secreting cells, although they are not very pronounced. The secretory activity of the cell was found to be correlated with a peak of mitogenic activity occurring in September/October in the case of the males and in November in that of the females. The secretion of gonadotropic mitogenic factor varies throughout the sexual cycle of Sepia officinalis. This activity is correlated with a rapid multiplication of spermatocytes and spermatogonia in the males, whereas in the females it corresponds to previtellogenesis.

Ilyanassa obsoleta (Say) (Mollusca: Neogastropoda) is a conspicuous biotic element of marine / estuarine habitats along the eastern North American coast. Growth among larger individuals (-18–30 mm shell height) has not been assessed. Trematode infections are common in this group and their effect on growth must be considered. Snails were individually marked, measured, and released on the Cape Henlopen sand-flat at the mouth of Delaware Bay. Shell height change (growth) and trematode parasitism were assessed in recaptured snails. Most or all growth occurred in June and July. Mean growth of uninfected snails was 1–2 mm per season. Snails that started out larger grew more slowly, but there was much individual variability. Mean growth of parasitized snails was 0–2 mm per season and independent of initial size. The maximum age of this snail is currently documented at 7 y, which is too low. Size reflects age only approximately. However, the minimum and maximum age of a snail of given size, based on maximal and minimal growth per season, can be estimated. A mid-range estimate for lifespan of unparasitized and parasitized individuals is 30–40 y.

The gut contents of 99 ballan wrasse (Labrus bergylta: Teleostei; Labridae) sampled between April and July in Galway Bay, Ireland and 95 ballan wrasse sampled between April and June in Dinard, Brittany, France were examined. Decapods and bivalves were the major prey categories in both areas, algae and gastropods were also frequently eaten but in much smaller amounts. The volume of the major food categories did not vary significantly with fish length. However, fish longer than 20 cm did consume greater volumes of bivalves than smaller fish. An increase in dietary diversity during the breeding season was observed. Ballan and corkwing (Crenilabrus melops) exploited many of the same food categories but with different emphases. Bivalves, which were major prey of corkwing, were also very important to the ballan captured simultaneously at the same site.

During the studies on sole recruitment in the Bay of Biscay, transport process attracted considerable attention and led to important research on migration and dispersal. The last step to complete the study of the spatial component of the life cycle of sole in the northern part of the Bay of Biscay is the offshore migration of young adults towards the spawning grounds. the present study deals with this pre-spawning migration. the main question concerns the kind of linkage between nurseries and spawning grounds. The principal results are based on extensive tagging experiments carried out in autumn 1992 in two distinct nursery grounds, Bay of Vilaine and Pertuis (4620 soles of 2-group and older). One year later (January 1994) catches of tagged individuals reached 18.1% and 11.9% of the initial samples, respectively. From September to February a 50-km net displacement of the centre of the population was observed towards the offshore deeper area. A small trend to move onshore appeared in spring. In parallel with these net movements individuals were dispersed around the centre of gravity of the population. This dispersion was higher in a direction parallel to the coast. Individuals from different nurseries were mixed over the same spawning areas of the Bay of Biscay, and some individuals were also captured in and close to the English Channel. Changes in distribution were in phase with environmental changes and some elements concerning topographic preferences also appeared. Some evidence for orientation was observed but random dispersal seemed more important. No particular link between a given nursery and a spawning ground in the vicinity appeared.

The distribution of 38 nests of loggerhead turtles (Caretta caretta) on beaches on Sanibel and Captiva islands, south-western Florida (26°26'N 82°16'W), and of 70 first digging attempts by green turtles (Chelonia mydas) on Ascension Island (7°57'S 14°22'W), was quantified. For loggerhead turtles on Sanibel and Captiva, nests were clumped close to the border between the open sand and the supra-littoral vegetation that backed the beaches. This spatial pattern of nests was closely reproduced by assuming simply that turtles crawled a random distance above the most recent high water line prior to digging. In contrast, green turtles on Ascension Island clumped their first digging attempts on the uneven beach above the springs high water line, crawling up to 80 m to reach this beach zone.

Nest temperatures for green turtles (Chelonia mydas) nesting on Ascension Island, South Atlantic (7°57'S 14°22'W), were examined. Temperature probes were placed into nests on two beaches, Long Beach (26 nests) and North East Bay (8 nests). Within these beaches there was relatively little thermal variation (SD of nest temperature was 0.32°C for Long Beach and 0.30°C for North East Bay). To examine inter-beach thermal variation temperature probes were buried at 55 cm on 12 beaches. Inter-beach thermal variation was large and was related to the beach albedo with the darkest beach (albedo, 016) being 4.2°C warmer than the lightest coloured beach (albedo, 0.73).

The copepod Lepeophtheirus salmonis Krayer (Copepoda: Caligida), the salmon louse, is a parasite of salmonids. The vertical distribution of the infective stage, the copepodid, was studied in salinity gradients with one step increase of 15‰ (154%e> on top of 304‰), 5‰ (25–4‰ on top of 30–4‰) and 2%> (28–4‰ on top of 304‰) in 1-m perspex columns. Copepodid distribution in a linear gradient, where the salinity increased from 154‰ at 0 cm depth to 304‰ at 87–5 cm, was also recorded. Homogeneous 304‰ salinity columns served as the control. In these, the animals gathered in the top section of the water column in response to 1 h of light from above, and spread downwards in response to 4 h of darkness. In columns with a 15‰ step increase in salinity with depth, copepodids aggregated just underneath the discontinuity irrespective of light conditions. In step salinity gradients of 5‰ and 2‰ S, under both light regimes, animals were significantly more numerous in the step sections compared with the control. In the linear gradient, significant numbers of copepodids accumulated at approximately 20‰ salinity when subjected to 1 h of light. In the dark, there were no significant aggregations. Copepodids were found in 15–17–2‰ salinity in all linear gradient experiments.