Long-term variations in shell growth of the mollusc Arctica islandica (Mollusca, Bivalvia) from the northern North Sea have been assessed retrospectively using the annually deposited internal growth lines. Relatively young specimens yielded a detailed year-to-year chronology while the growth record of specimens older than 30 y yielded a time series with a length exceeding 100 years. The long-term growth trends demonstrated a marked alternating sequence of periods in which growth was below and above expectation. A 33-y long cycle could be discerned. Since the 1960s the growth patterns in Arctica from two nearby locations were opposite, while they resembled each other in the period before 1960.

The cirral activity of the penduculate barnacle, Conchoderma auritum, was studied in a flow tank. The barnacles were exposed to different experimental water velocities and the response of the barnacles was recorded using a video system. In still and slow-moving water the barnacles show rhythmic cirral activity, the cirri extend and then withdraw into the mantle cavity. When water flow is accelerated the barnacles switch from rhythmic cirral activity to prolonged cirral extension, in which the cirri are extended in the water flow, facing the current. The water velocity at which barnacles switch from rhythmic activity to cirral extension depends on the size of the animal. During the rhythmic activity of Conchoderma water is pumped into the mantle through the ears. The prosoma serves as a piston which inhales the water into the capitulum and then ejects it at the apical end of the capitulum opening. This finding contradicts the generally accepted notion that the function of the ears of C. auritum is water ejection.

The present study confirms the findings that in the two ocypodid crabs Ocypode saratan and O. ryderi haemocyanin oxygen affinity is increased in ‘replaced’ or dialysed blood compared to whole haemolymph and that this difference can be attributed to a plasma factor. After the replacement of the plasma, the haemocyanin of both species showed up to a 39% increase in oxygen affinity. The change in oxygen affinity was proportional to the logarithm of the amount of native plasma present. Further investigations have shown that this difference is not due to changes in plasma urate or bicarbonate concentrations. Using plasma exchange experiments it could be shown that the factor acts specifically on the haemocyanin of Ocypode spp. and not on Carcinus maenas haemocyanin. Fast protein liquid chromatography (FPLC) techniques indicate that the molecular weight of the factor is <5000 daltons and a specific peak could be isolated. This isolated peak is linearly correlated with changes in haemocyanin oxygen affinity. The results are discussed in the light of the overall modulation of haemocyanin oxygen affinity and the need for negative effectors.

Mirocaris keldyshi gen. nov., sp. nov. is described from the Mid-Atlantic Ridge, TAG Location (26°09′N 44°50′W). The family Mirocarididae is proposed to include the new genus. The taxonomic position and distinguishing characters (presence of hook-bearing thoracic epipods and rudimentary appendix interna on pleopods 2–4) of the new family as compared to the other families of the superfamily Bresilioidea (Bresiliidae, Disciadidae, and Alvinocarididae) are discussed, and revised diagnoses for these families are provided.

Seasonal variation of clearance, absorption and respiration rates of mussels Mytilus edulis (Mollusca: Bivalvia) and cockles Cerastoderma edule (Mollusca: Bivalvia) of various size classes have been measured under ambient temperature and sea-water conditions. Food availability was kept almost constant during the measurements.

Allometric body weight coefficients were bcl=0.5 for clearance and about br=0.7 for respiration rate of both species. Stepwise multiple regression suggested no relation for clearance rate of mussels with temperature and reproductive condition throughout the year. Respiration rates of mussels were highest during the reproductive period. Excretion rate was measured for mussels only and showed an allometric coefficient of bex=0.7 and an increase with temperature in spring. For cockles a significant relation of clearance rate, body weight and temperature was observed; at low temperature, clearance rates of small animals were more reduced than for larger animals. Respiration rates of cockles showed a significant relationship with temperature and reproductive condition.

Trypsin-like enzyme activity of the larvae of two planktonic predatory crustaceans, Homarus gammarus and Nephrops norvegicus (Decapoda: Nephropidae) and the omnivorous larvae of Carcinus maenas (Decapoda: Brachyura) were investigated at each larval stage until metamorphosis. Two copepods, herbivorous or omnivorous grazers, Centropages typicus and Temora longicornis (Copepoda: Calanoidae) were also investigated for this enzyme. A comparison of trypsin-like activity in these and other decapod larvae shows a pattern with high levels in herbivores, low levels in carnivores and intermediate levels in omnivores. Herbivorous planktonic crustaceans appear to rely on high digestive enzyme activities to extract nutrients from less digestible algae or particulates, whereas carnivorous larvae have limited enzymatic capacity as they feed at higher trophic levels upon large and easily digestible prey. Omnivorous Carcinus maenas larvae have intermediate levels of digestive enzymes and are able to transfer between herbivorous and omnivorous feeding.

The digestive system of the thalassinidean mud-shrimp Upogebia stellata was investigated using scanning electron microscopy (SEM). Within the lumen of the midgut both filamentous and rod-shaped bacteria were observed. The hindgut microbial populations were dominated by dense mats of epimural rod-shaped bacteria. The gut contents were often dominated by diatoms but also contained bacteria, dinoflagellates, plant and algal fragments. Direct bacterial counts by epifluorescence microscopy along the length of the gut revealed a slight decrease in numbers within the midgut moving from the anterior to the posterior regions, and then a dramatic rise in numbers within the hindgut. Numbers decreased again in the posterior regions of the hindgut. Common in the transient / resident samples (bacterial population when gut contents were present) were enterobacteria and an unidentified fermenter conforming to an isolate named X-ferm. However, nearly 30% of the bacterial isolates remained unidentified. The resident-only bacterial isolates from the gut (determined when the gut was empty) were dominated by the X-ferm bacteria and to a lesser extent by the genera Vibrio and Aeromonas. With respect to the enzyme capabilities of the gut bacteria, the resident-only collection of bacterial isolates showed much higher levels of amylase, cellulase, chitinase, protease and lipase activity than the transient/resident bacterial isolate collections, suggesting that the indigenous bacteria are likely to play a significant role in the digestion of the gut contents. Thalassinidean shrimps are likely to play an important role in the breakdown of plant and detrital material, and the recycling of nutrients in marine benthic systems.

Two aspects of the physiology of the burrowing shrimp Caliianassa tyrrhena (Decapoda: Thalassinidea) were studied in order to investigate the effects of the general pollution load: total (TRR) and weight-specific respiration rate (SRR) as well as the digestive enzyme activity of the digestive gland.

Caliianassa tyrrhena exhibited a very low respiration rate (mean TRR=64-29 μl 02 animal−1h−1, N=60; mean SRR=0·18 μl 02mg DW−1h−1, N=61).

The slope of the TRR-DW logarithmic regression (b=0·64) showed that respiration in C. tyrrhena is proportional to body surface. Size is the dominant factor (among size, sex, season and locality) determining the variation in respiration rate. Comparison between the two sites with the different pollution load showed that there were no significant differences in the respiration rates of the same size class and season, except for the youngest animals in summer which showed a significant decrease in their respiration rate at the polluted site.

A similar ‘inhibitory’ effect of pollution has been observed in the activity of the majority of the 19 digestive enzymes tested. Only three e.g., trypsin, β-galactosidase and α-glucosidase showed an increase in polluted waters.

One could suggest, therefore, that C. tyrrhena can be considered to be preadapted to the low oxygen conditions encountered in the sediments, because of its burrowing mode of living.

The bresiliid shrimp Alvinocaris markensis is a predator that inhabits the base of sulphide mounds built by the black smoker chimneys of active hydrothermal vents at the Snake Pit site on the Mid-Atlantic Ridge. Casual examination of animals collected with theDSV ‘Alvin’ suggests that, like other biesiliid shrimp from hydrothermal vents, the eyes of this species are adapted for vision in very dim light. However, examination of the structure and ultrastructure of eyes of animals collected and immediately fixed shows that the expected massive array of photoreceptors is partially or completely missing. The eye is enlarged, its dioptric apparatus has disappeared, its screening pigment is essentially gone, and its reflecting pigment cells have formed an enlarged mass of white diffusing cells behind the expected layer of photoreceptors. In half of the animals examined, there were no recognizable photoreceptors in the retina, and in the remaining animals there were only scattered photoreceptors with poorly organized microvillar arrays of photosensitive membrane. We conclude that this species is blind despite some retinal adaptations for vision in very dim light. Apparently, the ambient light of this animal's environment is below the quit point (the minimum level that can be exploited) so that the retina has begun to degenerate by losing its photoreceptors.

The process of larval release in field collected ovigerous Carcinus maenas was monitored in the laboratory using a time-lapse video recorder. Under constant light (L:L) and simulated natural light/dark cycles (L:D), larval release normally occurred in two or more main events at about daily and/or tidal intervals. Since larval release in the crab was expressed with circadian and circatidal periodicity in continuous light and in the absence of tidal cues, it suggests involvement of endogenous timing. Crabs showing daily larval release rhythms released larvae at various times of the day in L:L. In contrast, under simulated L:D cycles, 37 out of 38 crabs released larvae during the dark phase, suggesting nocturnal release of larvae in the crab under natural conditions. Larval release from freshly collected females which shed larvae within two days of collection occurred predominantly around the times of expected nocturnal high tide. When both local semidiurnal high tides occurred in daylight during long summer days, larval release appeared to start 2–3 h earlier than the expected morning high tide, before the onset of daylight. Larval release at the time around high tide, linked to a previously described larval tidal migration rhythm of ebb-phased upward swimming, is likely to have been selected for by enhancing the larval offshore dispersal process. Nocturnal larval release is probably adaptive in the avoidance of visual predators by ovigerous females as they release larvae.

Five species of crabs were recorded in the Forth Estuary, of which Liocarcinus depurator and Cancer pagurus were confined to the lowest reaches where salinities are 24–35%‰. Carcinus maenas, Liocarcinus holsatus and Hyas araneus also occurred in the middle estuary where salinities are 22–31%‰ in summer but often fall to ~12%‰ in winter. A very few L. depurator and Cancer pagurus were confined to the lower estuary and mostly occurred in low tide trawls in summer. Carcinus maenas alone was recorded much further up the estuary where salinities rarely exceed 0–5·7%‰. Carcinus maenas predominated numerically throughout with an overall mean density of 0·0075 m−2 in the middle and lower estuary. Carcinus maenas in the estuary channel measured 16·6–82·9 mm carapace width (CW) with a modal size–class of 50–60 mm. Males were outnumbered by females (0·68:1 overall), and more markedly in summer than winter. Yet males were significantly bigger on average than females. Egg-masses were borne by 7·5% of all trawled females, but by 31·1% in April–May. On adjacent shores, by contrast, the much higher numbers of C. maenas were nearly all <20 mm CW. Low water trawls yielded significantly more C. maenas, but significantly lower proportions of males, than high water trawls. Liocarcinus holsatus was most abundant within the mid-lower estuary basin, with numbers decreasing both upstream and at the estuary mouth. Males outnumbered females by 2·26:1 overall, and most markedly at the extremities of the range. Males were significantly bigger than females, although sizes of both generally increased towards the mouth of the estuary. Only three of the 101 females bore eggs. Low water trawls yielded slightly more L. holsatus than high water trawls. Numbers of H. araneus increased markedly from mid-estuary to the estuary mouth where counts averaged 0·0021 m−2. Males outnumbered females by 2·17:1, and more so among those >40 mm CW. No female bore eggs. Records of the presence of C. maenas, Liocarcinus sp. and Hyas sp. all increased in the estuary from 1985 to 1995 reflecting increases in intertidal faunal diversity and changes in industrial practices since the early 1980s.

Ontogenetic changes in the body morphology, morphometrics, age, growth, maturation, fecundity, feeding spectrum and parasites were studied in 218 specimens of the oceanic nektonic squid Onychoteuthis banksi and in two specimens of the rare planktonic squid Chaunoteuthis mollis (Onychoteuthidae) caught in the tropical waters between 1977 and 1990. Similarities between the two species in major taxonomic features and in several morphometrical indices suggest that C. mollis is in fact a mature female of O. banksi with degenerated mantle and fin muscles and lost tentacles. Thus, C. mollis will be considered as a lesser synonym of O. banksi. Statolith microstructure analysis reveals that O. banksi is a slow-growing squid with low maturation rates, spending the first 240–260 d of life in the epipelagic zone. The main features of the reproductive strategy include earlier maturation of the males, small eggs (0.2–0.5 mm in diameter by the end of protoplasmic growth), synchronous development of oocytes and high potential fecundity (51,000–205,000 eggs). Onychoteuthis banksi is an opportunistic predator, shifting to a fish and squid diet much earlier and at smaller sizes (20–40 mm ML) than ommastrephid squid. The feeding activity of small and medium O. banksi (20–80 mm ML) is a little higher and that of large O. banksi (80–148 mm ML) is lower than in ommastrephids of the same size. The helminth fauna of O. banksi is impoverished and consists of ‘food parasites’: larval Didymozoidea and Scolex spp. The level of infection is low, only reaching -52 specimens per host in large squid. The nature of the life cycle of O. banksi and possible evolutionary trends in the development of the ‘Chaunoteuthis’ stage for maturation and spawning of females in the deep water are discussed.

Behaviour during homing movements and downstream migration of yellow- and silver-phase American eels (Anguilla rostrata) was observed using continuous ultrasonic telemetry in a tidal estuary. Homing subadult (yellow-phase) eels, non-displaced yellow-phase eels and adult (silver-phase) eels all used tidal currents as a transport mechanism (‘selective tidal stream transport’) and possibly as a means of orienting and moving in an appropriate direction. Yellow-phase eels displaced up the estuary and migrating silver-phase eels moved mostly at night and during ebbing tides. Yellow-phase eels displaced down the estuary moved mainly during flooding tides both day and night. Non-displaced eels used selective tidal stream transport to make long, round trip excursions and to move about their home range. Eels were at or near the surface during most of their movements, but were also vertically active, diving transiently to mid-water or to the bottom. During movements, the eels tended to drift with the current, or to swim slowly in the direction of the current. Although they used the tidal currents effectively as a transport mechanism, they were not precise in timing their movements to maximize transport on each tide. This study demonstrates that both yellow- and silver-phase eels use selective tidal stream transport during movements in tidal habitats and excludes some cues previously proposed to regulate the behaviour.

The diversity and distribution of the Bivalvia fauna is examined in the various seas of Greek territorial waters. There is a statistically significant correlation between the bibliographical sources and the recorded variety of Bivalvia at any given area, with the deeper areas containing fewer species. Attention is given to some species ‘introduced’ into the area.

Cluster analysis, based on the species present at 30 regions which represent distinct geographical and ecological units, do not show any differentiation that corresponds to a geographical pattern. However, a distinct group is associated with the deeper open areas, which suggests that ecological parameters, such as depth and degree of enclosure, play an important role in the distribution of species.

Columbus crabs, Planes minutus (Crustacea: Brachyura) live in the open ocean attached to floating substrata including Sargassum, flotsam, and sea turtles. Eighty-two percent of 128 loggerhead turtles (Caretta caretta) checked, harboured a total of 172 crabs. Crabs inhabiting flotsam occurred in mixed sex groups of adults and juveniles, with a mean group size of 8.2 ±;11.8 (N=17). In contrast, crabs living on sea turtles around Madeira occur in smaller groups 1.6 ±0.5 (N=105) which are typically adult heterosexual pairs (61 out of 105). Crabs on turtles were bigger than on flotsam and a higher proportion of female crabs were brooding eggs. Columbus crabs exhibit different life history strategies depending on the substratum they inhabit.

Recent attention to members of the sepiolid squid genus Euprymna and symbiotic associations with luminescent bacteria (Vibrio fischeri strains) has prompted a review of this poorly-resolved group of squids. Twelve nominal species have been placed in this genus of which the majority are ill-defined, known only from their original descriptions and separated on the basis of inadequate characters. As a first step in resolving this group, a temperate Australian species, the Southern dumpling squid, Euprymna tasmanica, is here redescribed in detail. As the genus Euprymna currently stands, most members are only distinguished on the number and position of enlarged suckers in mature males. No diagnostic characters are available to identify females. All nominal species placed in this genus are reviewed and a key to proposed valid species is presented. Six species are considered here to be valid: Euprymna berryi, E. hoylei, E. morsei, E. scolopes, E. tasmanica and an undescribed species treated here as Euprymna sp. 1. Euprymna similis is a synonym of E. morsei of Japan. Due to inadequate original descriptions, and lost or poor type material, two species are considered here to be nomen dubia (E. schneehageni and E. pusilla), while the taxonomic status of four additional species remain unresolved (E. albatrossae, E. bursa, E. phenax and E. stenodactyla).

Trace metals are accumulated by marine invertebrates to body concentrations higher, in many cases orders of magnitude higher, than the concentrations in an equivalent weight of the surrounding sea-water (Eisler, 1981; Rainbow, 1990; Phillips & Rainbow, 1993). Specific details of trace metal accumulation processes vary within the same invertebrate species between metals, and for the same trace metal between invertebrates, often between closely related species (Rainbow, 1990, 1993). This short review attempts to highlight some of the comparative aspects of the processes involved that are expected and explicable in terms of the chemistry of the respective elements, and those where the physiology of the species involved intervenes to offset predictions from purely chemical principles. Although an appreciation of trace metal chemistry is crucial to an understanding of trace metal accumulation, idiosyncrasies in the biology of the invertebrate (at any taxon level) may intervene to bring about significant and unexpected comparative differences in metal accumulation patterns.

Two bacteria-bearing mussels, Bathymodiolus brevior and B. elongatus, collected at five deep-sea hydrothermal sites from Lau and Fiji back arc basins (south-west Pacific), were analysed for polar and neutral lipids using gas-liquid chromatography mass spectroscopy (GLC-MS). The respective fatty acid distributions found in gills and mantles were compared to data from a Mediterranean littoral filter-feeding mussel, Mytilus galloprovincialis. The main characteristic common to the gills of the two vent mussels was the high level of (n-7) monounsaturated phospholipid fatty acids, which are supposed to originate from sulphur-oxidizing symbionts. Using palmitoleic, 16:1 (n-7), and vaccenic, 18:1 (n-7), phospholipid fatty acids as bacterial markers, endobacterial biomass was estimated to account for 2–10% of the vent mussel gill volume. Vent mussel tissues were poor in plant-derived polyunsaturated fatty acids, indicating the limited importance of the photosynthesis based material in the metabolism of these hydrothermal vent bivalves. It is suggested that some compounds, such as nonmethylene-interrupted dienoic fatty acids and specific trienoic fatty acids originating from elongation and desaturation of oleic and palmitoleic acids, respectively, were synthesized in order to substitute exogenous plant-derived polyunsaturated fatty acids considered as essential in marine invertebrates. The high level of neutral lipids in vent mussel gills suggests that these compounds are used as a major energy storage material. The neutral lipid/phospholipid ratio in gills emphasized the preponderance of the endosymbionts in vent mussel nutrition. Using this ratio as an index of the physiological state, the symbiosis patterns in different hydrothermal fields were compared.

Allozyme electrophoresis was used to estimate the genetic divergence between three species of South African Helcion and the north-east Atlantic H. pellucidum (Patellidae). At a finer level the genetic relationships among South African Helcion were explored. Twenty-one loci were resolved for all the species. High values of expected heterozygosities (0·202–0·341) were found for the genus. Phenetic analysis (UPGMA (unweighted pair-group method with artihmetic averaging) and Distance Wagner Procedure) and cladistic parsimony methods (alleles as binary characters and loci as multistate unordered characters) agreed in showing the same topology for the tree which represents the genetic relationships among Helcion species. The north-east Atlantic H. pellucidum was the most divergent species showing high values of Nei's genetic distances (1·423–1·654) with its South African congeners. In the literature such values of genetic divergence have been associated with non-congeneric species. The degree of genetic divergence (0·351–0·615) found within the South African branch was characteristic for congeneric species. The results of this study supported the monophyletic condition of this branch, and showed H. pectunculus and H. pruinosus to be more closely related to each other than to H. dunkeri. Nevertheless, the monophyly of the genus Helcion is uncertain and therefore its taxonomic status was questioned. A possible independent origin for northern and southern hemisphere species of Helcion is considered.

Underwater behavioural observations were conducted to evaluate the relative importance of cleaning behaviour in three species of common north-eastern Atlantic wrasse (Teleostei: Labridae). At the study site, the only cleaner was Centrolabrus exoletus. A total of 12 species was cleaned, with the wrasse, Symphodus melops and Labrus bergylta being the species most frequently cleaned. Neither S. melops nor Ctenolabrus rupestris, known to be cleaners in other sites or in captivity, could be observed cleaning other fishes. Centrolabrus exoletus was found to be a facultative cleaner fish with cleaning acts representing only 7% of the observed feeding acts. In focal observations of host fishes, the incidence of cleaning acts reached a level (11 h-1 per host) similar to that reported for tropical reef fishes and probably reflects the high numbers of cleaners available. Some factors that may affect the origin of the cleaning interactions are discussed.