The vertical distributions and diurnal migrations are analysed for nineteen species of calanoid copepods in the families Lucicutiidae up to and including the Candaciidae. The relative abundance, both vertical and horizontal, is given for each species.

With few exceptions most of these species show little or no vertical migration. There is some suggestion of a reversed (downward) migration for Paracandacia bispinosa andP. simplex but since there are difficulties in analysing the surface samples the evidence is inconclusive. The species which are abundant in the family Heterorhabdidae all have little or no vertical migration and are at least partially vertically segregated by both day and night. Phyllopus impar and P. helgae are clearly vertically segregated and Haloptilus acutifrons and, to a lesser extent, H. ornatus each have two vertically separated populations by both day and night. Two size groups are present in each sex of Lucicutia flavicornis.

The vertical distributions and numbers throughout the water column are analysed for 203 and 176 species in the day and night series respectively; it is concluded that while many species are relatively abundant at one or more particular depth most of them are numerically relatively insignificant in the water column as a whole. Only two species (day) and four species (night) formed more than 5 % of the total numbers caught in their respective series.

The relative abundance, both vertical and horizontal, of the commonest genera are analysed. In the whole water column the relative abundance of most of the genera is constant by both day and night, and, as with the individual species, most of them are relatively scarce.

The deep sea protobranch bivalve species Ledella pustulosa recently has been described as comprised of four subspecies, differentiated on subtle and qualitative differences in shell morphology. Two of these, L. p. pustulosa and L. p. marshalli, possess overlapping geographic distributions, L. p. pustulosa occurring on the continental slope, and L. p. marshalli occurring on the continental rise and at upper abyssal depths. Principal components analysis was applied to six samples of Ledella pustulosa from the Rockall Trough in order to explore patterns of variation in shell shape and to test whether the variability follows a depth-related cline which might be under environmental control. Two of these samples had previously been identified as L. p. pustulosa and L. p. marshalli, respectively. The distributions of shapes at every depth overlapped broadly with the distributions from other depths and none of the depths had uniformly distinct shells. However, the mean shapes of the six samples divided into two clusters: a shallow cluster characterized by a lower dorsal profile (smaller ‘shoulders’) and a deep cluster with larger ‘shoulders’. No bathymetric cline in shape was found within these clusters. A discriminant function based on training samples of L. p. pustulosa and L. p. marshalli correctly identified 84% of the shells in the training samples and was applicable over a wide range in shell size. It showed that the subspecies differed primarily in the dorsal profile. The discriminant function was applied to 598 shells from depths of 1632–2900 m in the Rockall Trough in order to test the hypothesis of depth-related segregation of the subspecies. Although individual variability was high, the results indicated a gradual transition from L. p. pustulosa dominance at ∼2000 m to L. p. marshalli dominance at 3000 m depth, but not marked segregation. A sample from 1632 m depth with large proportions of both subspecies disrupted the bathymetric trend and suggested a latitudinal gradient in distribution. Possible environmental factors, including bottom currents, acting on a common genotype to cause the observed pattern of differentiation, are also discussed.

The short-term variability of intertidal microphytobenthic biomass was characterized by analysing a 30-day time series encompassing two spring–neap tide cycles. Chlorophyll-a concentration was measured every day at the beginning and at the end of every diurnal exposure periods. Microalgal biomass exhibited predictible net increases during diurnal exposures due to a positive production-loss balance. In addition, our data series shows that after an environmental disturbance, even though biomass decreased strongly, it converged quickly back to its initial steady-state oscillation pattern. This study supports some fundamental properties of the dynamics of microphytobenthic biomass, as previously predicted in our mathematical model of primary production.

Using acoustic telemetry techniques, the movements and habitat utilization of anadromous Arctic charr (Salvelinus alpinus) were determined when they entered the Freshwater Creek Estuary (Cambridge Bay, Northwest Territories, Canada) in the spring. The study was carried out during the transition from full ice cover to open water.

Between 23 June and 1 July 1996, nine adult Arctic charr were tagged with external acoustic transmitters. These fish were tracked until 6 July using two radio-linked acoustic array systems and a portable manual receiver with a directional hydrophone. Two transmitters measured temperature and location, one measured depth and location and the remaining six, location only.

All of the tagged charr remained in Cambridge Bay Estuary until the sea-ice had melted and the mouth of the bay was ice-free. Primarily, they remained in the warmer brackish surface layer which was ∼2 m thick and rarely moved into the colder underlying marine waters. As well, the tagged charr remained either near the shore or over offshore shoals, following the ice-edge as it melted down the estuary. Residence time in the estuary was greater than ten days for some fish. Therefore, in spite of evidence from controlled laboratory studies that have shown that Arctic charr are preadapted to the marine environment and are capable of migrating directly into seawater, this study shows that, in the wild, they prefer to remain in warmer brackish water until the sea-ice has melted and that the transition stage is longer than previously suggested.

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.

Considerable obscurity surrounds the mechanism of calcification in all biological material. The coralline algae, which lay down quantities of calcium salts in their tissues, are no exception. These forms are common in the littoral and sublittoral in exposed situations in northern waters and make up a large part of many of the reefs in tropical seas. This paper describes observations and experiments relating to growth and calcification in two northern corallines, Clathromorphum circumscriptum Foslie and Corallina officinalis Linn. Calcification is related to the production of an alkaline reaction by the cells when exposed to sunlight. The source of the base concerned will be considered in a following paper.

Glass sponge reefs on the continental shelf of western Canada and south-east Alaska are considered stable deep-sea habitats that do not change significantly over time. Research cruises using a remotely operated vehicle equipped with accurate GPS positioning have allowed us to observe the same sponges at two reefs in the Strait of Georgia, British Columbia to document recruitment, growth and response to damage over time. Spermatocysts and putative embryos found in winter suggest annual, asynchronous reproduction. Juvenile sponges (2–10 cm in osculum diameter) in densities up to 1 m−2 were more concentrated near live sponges and sponge skeletons than away (Spearman rank correlations, P < 0.0001 for live cover and for skeletons), suggesting that recruitment occurs in particular regions using sponge skeletons as substrate. Most sponges showed no change in shape or size over 2–3 years, but some had died while others showed growth of 1–9 cm year−1. Deposition rates of reef-cementing sediments were 97 mm year−1 at Galiano Reef and 137 mm year−1 at Fraser Reef, but sediments eroded so that there was no net gain or loss over time. Sponges recovered within 1 year from small-scale damage that mimicked bites by fish or nudibranchs; however sponges did not recover from crushing of a large area (1.5 × 2 m2) even 3 years later. These observations and experiments show that while recruitment and growth of sponge reefs is more dynamic than previously thought, the reefs are not resilient in the face of larger-scale disturbances such as might be inflicted by trawling.

Reproductive phenology among temperate hermit crabs, reproductive seasons of nine sympatric species and some reproductive characteristics of four Pagurus species were investigated in Tosa Bay, southern Shikoku, Japan. Females of P. filholi, P. maculosus, P. minutus and P. nigrivittatus had clutches mainly in winter and were found to breed multiple clutches within each reproductive season while four Diogenidae species and P. japonicus mainly reproduced in summer, suggesting that interspecific variation in reproductive phenology of temperate hermit crabs might be determined by allopatric adaptation with phylogenic constraints. There was interspecific variation in the length of reproductive seasons among the four Pagurus species and the variation was considered to reflect the interspecific difference in the number of clutches per reproductive season, not in the ovigerous period per clutch. The length of reproductive seasons among the four species seemed to relate to maturity size and/or interspecific differences in thermal adaptation.

The diet of Sepia officinalis was studied by examining the stomach contents of 522 specimens caught off the coast of the Algarve, Portugal. A total of 49 different prey items, belonging to six taxa (Polychaeta, Cephalopoda, Teleostei, Bivalvia, Crustacea and Gastropoda) was found, indicating opportunistic feeding behaviour. The diet was examined in relation to season, sex and size. The diet of males and females were similar. For small S. officinalis, crustaceans were more important in weight, whereas for larger specimens, fish were dominant. Seasonal differences in the diet were apparent but were shown to be possibly influenced by the cuttlefish size.

The life history of Sacculina carcini parasitic on Carcinus maenas in the Clyde sea area is discussed and the breeding period and the time of the emergence of the young externa are indicated. The time and duration of the breeding season are compared both with what has been found at Plymouth and Roscoff for the same species of parasite on the same host crab, and also with what was found by Day (1935) who worked in the Mersey area on Sacculina carcini but parasitizing Portunus holsatus.

The length of life of the Sacculina externa and their ultimate fate are discussed. It is shown that in male crabs which act as hosts the liability of the secondary sexual characters to modification is correlated with size.

The general biology of Erythrops serrata (G. O. Sars) and E. elegans (G. O. Sars) is described. There are two main generations of E. serrata, a spring and a summer one, produced during the year although continuous breeding at lower intensities is present in the population between the most productive periods; females carry 14–18 young per brood in the spring and summer but these numbers decrease to 4–8 in winter broods. The marsupium of E. serrata is often lost after the brood emerges. The few data available for E. elegans suggest that its breeding behaviour is similar to that of E. serrata but fewer young per brood appear to be produced by this species. Both species feed on the surface layers of the bottom and the material in suspension, but E. serrata had, on occasion, remains of crustaceans among its stomach contents, indicating a carnivorous diet.

The nematocysts of five species of Anthomedusae, six species of Leptomedusae, and one Trachymedusa are described.

In view of the additional support supplied by characters of its nematocysts it is suggested that the genus Chromatonema should be placed with Tiaranna in a new family, the Tiarannidae, in the Anthomedusae.

Evidence on the possible evolution of microbasic euryteles from stenoteles is afforded by the nematocysts of Aglantha.

Pelonaia corrugata in the Firth of Clyde breeds for only 2–4 weeks in January or February. The species is oviparous. Early cleavage is similar to that of other ascidians, but after gastrulation the embryo passes through a two-hemisphere stage. One of these hemispheres is endodermal. From the other hemisphere, which slowly envelops the endoderm, two ampullae grow and fix the embryo to the substratum. The young ascidian develops directly from this attached embryo, and the development is therefore anural. Elimination of the pelagic larval stage is regarded as an adaptation to the sand-dwelling habit of the adult, as it prevents dispersal to unsuitable habitats.

To determine whether modern theories predict snail growth responses to trematode infestation a field growth study of Onoba aculeus, Littorina saxatilis and L. obtusata infected with two closely related Microphallidae trematodes was conducted in the White Sea. In each of the three host–parasite combinations studied trematode infection causes inhibition of snail reproduction. However, contrary to the classical interpretation of the gigantic growth of infected snails as a side effect of parasitic castration, the presented study failed to demonstrate that Microphallus piriformes causes gigantism in Littorina. The infection tended to stunt growth in L. obtusata and had no significant effect on growth rate of L. saxatilis. In contrast, gigantic growth was observed in O. aculeus infected with M. pseudopygmaeus. Considering that both trematode species are very similar biologically, the discrepancy is attributed to differences in the life history of the snail's hosts. Onoba aculeus is a relatively short-lived snail (2.5–3 y). The lifespan of L. saxatilis and L. obtusata is much longer (up to 9–11 y). These findings agree with a previously reported ‘energetic’ hypothesis that predicts growth alterations in accordance with life history variations of the snail species.

In 1998, in coincidence with high sea surface temperatures, Maldivian reef corals were severely affected by mass mortality following bleaching. Tabular Acropora corals, formerly abundant in shallow water, were nearly exterminated. Recovery started soon, and in 2004 Maldivian reefs appeared rich in tabular Acropora colonies again, especially at some sites. This study aimed at determining the degree of spatial variability of tabular Acropora abundance and size among reef typologies (ocean versus lagoon reefs) and depth zones (4–6, 10–12 and 16–18 m) 6 years after the mass mortality event. A total of 192 tabular Acropora colonies (Ø > 16 cm) were counted and measured in six sites. Their abundance differed between reef typologies and according to depth zones, with the highest values in deep lagoon reefs. Colony mean size differed only among depth zones, the largest colonies (up to 105 cm) being found in shallow reefs. Assuming a radial extension rate of 10 cm · yr−1, colonies larger than 65 cm can be interpreted as the survivors of the mass mortality of 1998; conversely, they may represent the result of enhanced growth rates in uncrowded situations as those characterizing the coral reefs of the Maldives in 2004.

Intertidal individuals of Mytilus galloprovincialis were exposed to anaerobiosis in laboratory at 22°C and a set of biochemical metabolites and survival potential determined. Differences in survival potential between individuals emersed or kept in oxygen-free seawater were residual according to ST50 values (survival time, P[asymp ]0.05) but emersed individuals survived significantly longer when considering ST90–100 values (P<0.05). Anaerobiosis was similarly activated under both emersion and incubation in anoxic seawater after 6 h according to a seven-fold increase in succinate. Longer exposure of individuals (up to 48 h) caused succinate (and propionate) to increase but in a higher magnitude under incubation with anoxic seawater. Propionate appeared in soft tissues after 24 h of incubation in anoxic seawater and after 48 h when individuals were emersed. Glycogen was not utilized after 6 h in any case, but was progressively used with longer exposure times and in a higher magnitude under incubation in anoxic seawater (48 h). Adenylate energy charge (AEC) was highly affected by both exposure time (P<0.001) and anaerobic treatment (P<0.01). Rapid breakdown of ATP and phospho-L-arginine (PLA) did occur during the first 24 h of anaerobiosis, the latter ATP drop was accompanied by slight increase of ADP but strong increase of AMP that accumulated in a higher magnitude under incubation in anoxic seawater. Biochemical results of the present study suggested a certain degree of aerobiosis for emersed M. galloprovincialis that in turn is linked to a slight but significant longer survival performance. Most significant biochemical changes occurred during the first 24 h of oxygen deprivation, but significant differences between treatments were observed after 24–48 h. These lag differences in biochemical metabolites together with more accurate survival analyses have to be considered when investigating the energy metabolism linked to the anaerobic performance of M. galloprovincialis.

A high degree of variation in hydrographic conditions is found in the so-called Iroise Sea, within less than 100 km of the west coast of Brittany. Tidal current maximal velocity, especially, ranges there from about 0·5 knot to more than 8 knots (locally, near the island of Ushant), i.e. practically as wide a range as found over the whole of north-west European shelf seas. Pelagic ecosystems accordingly exhibit a high degree of variety, related not only to classical inshore-offshore gradients, but also to the extent of vertical mixing or stratification. Areas where different physical and biological conditions prevail are generally separated by rather clearcut boundaries. The better-known of these is the Ushant thermal front, which runs in summer across the whole entrance to the English Channel, but also extends into the Iroise. In addition, freshwater runoff results in thermohaline stratification, or at least in the existence of thermohaline vertical gradients, in the two major bays of the west coast of Brittany. The relevant area is limited seawards by a thermohaline front, the Iroise inner front (Grail & Le Fèvre, 1967; Le Fèvre & Grall, 1970), beyond which are found the well-mixed waters inshore of the Ushant front. Fig. 1 sums up these hydrographic patterns in the area taken here into consideration.

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.

Canopy-forming fucoid algae have an important role as ecosystem engineers on rocky intertidal shores, where they increase the abundance of species otherwise limited by exposure during low tide. The facilitative relationship between Ascophyllum nodosum and associated organisms was explored using a frond breakage experiment (100%, 50%, 25%, 0% intact-frond treatments) in southern England, to assess the consequences of disturbance. Understorey substratum temperature was on average 3°C higher in 0% and 25% intact-frond treatments than in plots with 50% and 100% intact fronds. Light (as PAR during low tide) doubled in 0% intact-frond treatments in comparison to other treatments (which had similar light levels). Mobile invertebrate species richness declined by on average 1 species per m2 in the treatments with only 25% and 0% intact fronds, and the abundance of Littorina obtusata declined by 2.4–4.2 individuals per m2 in the treatments with 25 and 0% intact fronds. Sessile taxa, including Osmundea pinnatifida and encrusting coralline algae, declined by half on average in the 0% intact-frond treatment. These results suggest that the ability of Ascophyllum to mediate environmental conditions to the understorey is the mechanism responsible for species distributed in the understorey (autogenic ecosystem engineering). The results of this study imply that a pulse disturbance resulting in a 50% breakage of Ascophyllum fronds significantly increases temperature and decreases the abundance of mobile invertebrates usually associated with Ascophyllum. Sessile taxa associated with Ascophyllum can, however, withstand disturbances down to 25% intact Ascophyllum fronds.

Male and female sharknose cleaning gobies Elacatinus evelynae (Gobiidae) occupying cleaning stations in monogamous pairs differed significantly in cleaning behaviour and diet. Females spent five times longer cleaning, took more bites from clients, engaged in more cleaning events on more client species, and cleaned at a higher rate than males. These behavioural differences tended to be reflected in the diet, with more females ingesting more client-gleaned items than males. These results are consistent with greater energetic requirements for reproduction for females. Male cleaning gobies were frequently absent from cleaning stations, presumably guarding eggs, and their presence at cleaning stations gave rise to foraging conflicts and interactions with females. The cleaning rate of females was significantly lowered by the presence of males, whether cleaning or not, whereas males cleaned for longer and took more bites when females were present. When cleaning the same client, males and females showed priority of first inspection, with females cleaning longer and taking more bites in cleaning events they initiated while males gained similar advantages in client- and male-initiated interactions. Furthermore, females initiated cleaning on larger clients, which may give them a foraging priority on a higher-quality resource since larger clients tend to have more ectoparasites. Finally, from a client's perspective, the cleaning service provided appears better in terms of length of inspection and bites taken when both males and females are at a cleaning station than when a single cleaner is present. However, the foraging differences and interactions between male and female cleaning gobies are of little consequence to clients since the cleaning service provided is simply reapportioned between males and females rather than changed by the interactions between gobies.