A radical change in the abundance of invertebrate megafauna has occurred over a vast area of the Porcupine Abyssal Plain, north-east Atlantic, in recent years. In particular, the holothurian Amperima rosea has increased in abundance by three orders of magnitude. The sudden increase in abundance of A. rosea appears to be the result of environmental forcing rather than localized stochastic population variations. Amperima rosea produces small eggs ([les ]200 μm) indicating (1) planktotrophic larval development or (2) lecithotrophic larval development with an abbreviated larval stage. It also reaches maturity at a very small size. The reproductive biology of A. rosea indicates that it can increase rapidly in population size and can colonize large areas quickly. It has high fecundity, as predicted by gonad indices and observed in histological studies. Fecundity was greater in winter than in summer months, but there was no clear evidence of seasonal or episodic reproductive events. All males, irrespective of sample season or year, were mature with spermatozoa. Most oocytes were of an intermediate size (70 to 120 μm), either at the late previtellogenic (70–90 μm) or early vitellogenic (100–120 μm) stage of development. It is postulated that development of full vitellogenesis, leading to episodic spawning, might be dependent on certain environmental stimuli. The most likely stimulus is food supply. Amperima rosea has been shown to feed preferentially on phytodetritus and to have a requirement for certain sterols in its diet. Qualitative changes in the flux of organic matter to the sea-floor may control vitellogenesis and fecundity, and hence have an effect on the population dynamics of the species.

A new neritiliid gastropod, Neritilialittoralis, lives in a unique, intertidal, subterranean, brackish environment on Amami-ohshima Island, Japan. It lives exclusively on rubble that is embedded deeply in coarse-grained sand whose interstices are filled with a mixture of subsoil water and seawater. Empty shells of this species were also found in tide pools at the foot of limestone terraces on Okinawa Island, where a large volume of karst-related freshwater gushes out. The species is characterized by a very small, white shell and unpigmented skin. Neritilia has previously been found in freshwater streams, rivers, estuaries, and in anchialine and phreatic waters, and the present find expands its range of known habitats and has implications for the history of the invasion of freshwater by neritiliids. The spiral protoconch suggests that the larva of N.littoralis is long-lived, planktotroph and a very effective disperser, and all the individuals collected appear to be part of a panmictic population.

This study tested the hypothesis that regularly-shaped sandstone blocks in intertidal boulder-fields are colonized by mobile macrofauna at a similar rate to colonization of natural boulders. In addition, the sessile component on these plates (three levels of sessile assemblages) and their position in the boulder-field (three different positions relative to other boulders) were varied to test hypotheses about effects of these features on colonization. The epibiota varied among the three sets of plates and the natural boulders at the start of the experiment. The boulders were very rapidly colonized by a suite of mobile animals, particularly chitons, gastropods and echinoderms. Colonization was sparse and patchy to start with, causing great variability among replicates. Nevertheless, it did not differ among any of the treatments, indicating that even at this early stage, colonization did not differ between natural boulders and blocks, nor according to the sessile assemblage, or the proximity of other boulders. By six months, there was little variability among replicates and the assemblages had converged. This indicates that sandstone plates/blocks can form a standardized unit of habitat which can be used to test models about spatial variation in this relatively specialized fauna.

The functional reproductive system of three Mediterranean species of Coralliophilidae (Gastropoda: Prosobranchia), Coralliophila brevis, Coralliophila meyendorffii and Babelomurex cariniferus, was compared with that of Coralliophila squamosa and three Leptoconchus species. Differences chiefly in the pallial section of the female reproductive tract separate the Indo-Pacific genus Leptoconchus from the Mediterranean species, and subdivide the latter into three different anatomical groups. Polyphyly of the genus Coralliophila is suggested. Comparison of the reproductive system of coralliophilids with that of the related Muricidae allows identifying characters of Coralliophila brevis, Coralliophila meyendorffii and Babelomurex cariniferus that are unknown in Muricidae. The comparison also reveals a closer similarity of Coralliophila squamosa with Ocenebrinae, suggesting that this species might represent a less derived evolutionary line within Coralliophilidae. The reproductive system of some individuals of Coralliophila meyendorffii and Babelomurex cariniferus undergoing penis reduction in the laboratory is also studied. It sheds some light in the ontogeny of the female pallial reproductive tract, and provides direct evidence for the existence of protandry in these species.

Sulphur-isotopic composition of soft tissues from Bathymodiolusmarisindicus collected from hydrothermal vents in the Indian Ocean was reported. The δ34S values of the soft tissues (+3∼+5‰ vs Cañyon Diablo troilite) were nearly identical to those from the associated hydrothermal fluid and chimney sulphides (+5 to +8‰), but were significantly different from that of the common seawater sulphate (+21‰), which suggested that the endosymbiotic bacteria used sulphide in the fluid as an energy source. Transmission electron microscopic observation of the endosymbionts also suggested that the symbiont is a thioautotroph. Bathymodiolus species, which depend on either sulphide or methane oxidation, or both, have a worldwide distribution. Bathymodiolus marisindicus from the Indian Ocean has a close relationship with congeners in the Pacific Ocean as evidenced by form of symbiosis. Biogeography and migration of the genus Bathymodiolus based on the relevant data are briefly discussed.

Seasonal changes in the diet composition and trophic niche overlap were examined for the dominant members of the fish assemblage of the turbid low-salinity zone of the Scheldt estuary (Belgium). Samples of fish were taken in the cooling water of a power plant. Juveniles of eight species dominated the fish assemblage: two goby species, herring, sprat, bass, flounder, eel and pikeperch. Together, they had preyed upon 31 different prey taxa. Calanoid copepods and hyperbenthic mysids were the most important prey items with macrobenthic invertebrates being largely ignored. Pair-wise comparisons of trophic niche overlap showed that, in general, niche overlap between individuals of the same species was significantly higher than overlap between individuals from different species, suggesting that the available food resources were partitioned. The total annual prey consumption by the dominant fish species was estimated at 610 mg ash-free dry weight m−3.

The presence of angiotensin I-converting enzyme-like activity (ACELA) was investigated in whole body homogenates of Branchiostoma lanceolatum using a highly sensitive fluorimetric assay. The measured enzyme activity was inhibited by the two angiotensin converting enzyme inhibitors, captopril and enalapril, suggesting a biochemical pathway that could generate the angiotensins observed in the central nervous system of amphioxus.

Ilyanassa obsoleta (Mollusca: Gastropoda) is an abundant inhabitant of salt marshes and tidal flats on the east coast of North America. Populations of this snail may be heavily infected by larval trematodes. Three species were observed in this work, Himasthla quissetensis, Lepocreadium setiferoides, and Zoogonus rubellus. Mostly as single-species infections, all occupy snail tissues as parthenitae that produce cercariae, which are released from the snail to infect the next host. By periodically testing snails for cercarial emission, single-species infections are here shown to persist over six summers and double-species infections are also noted to be long-lived. Among the 32 snails followed, 25 released the same (or no) cercariae throughout observation periods averaging three years. The other seven indicated infection changes, but only two of these are judged to reflect actual changes. The probability that a snail changed infection status in this study is thus 2.1% y−1. Ilyanassa obsoleta individuals, and apparently their trematode infections, can persist for decades. Because species colonize and get evicted infrequently, sets of trematode species infecting I. obsoleta individuals (infracommunities) are concluded to be isolationist in character.

The chromosome number and karyotype of amphioxus Branchiostoma belcheri tsingtauense were studied using embryonic cells. The diploid chromosome number (2n) of B. belcheri tsingtauense is 36, and its karyotype 2n=36, 2st+34t, FN=36. This is the first report on the karyotype of the cephalochordate. Evidence suggesting the possible presence of a pair of sex-chromosomes in the amphioxus has been provided.

The composition of meiobenthic and macrobenthic communities between different intertidal reef-flat pools on Rocas Atoll (South Atlantic) was compared, and related to properties of the carbonate sediments and patterns of reef growth. Both univariate and multivariate statistical analyses showed that the reef height and size influenced the properties of the reef-derived sediments and were correlated with the composition and abundance of the benthic fauna in the intertidal pools. The temperature and the salinity between Rocas tidal flat reef pools did not vary significantly, despite the differences in size, exposure degree and elevation, suggesting that percolation through the porous lime body of the reef and/or the connection between the tidal pools and seawater by blowholes have a significant effect on the tidal pools. The major asymmetry in the reef topography of Rocas Atoll was observed between the leeward and windward reefs, which paralleled the largest changes in sediment properties and faunal structure inside intertidal reef pools. Sediments from the tidal pools located in the windward side of the atoll were significantly finer, the organic content higher and the benthic fauna more abundant and diverse. The results of this study suggest that significant changes in the sediment properties and benthic community structure between the intertidal reef-flat pools of Rocas Atoll may be primarily conditioned by different patterns in reef growth.

Patterns of distribution of a Mediterranean fish assemblage, with special attention to juvenile labrids, were studied at different depths on the basis of their relationships with environmental and benthic habitat features on a rocky coast at Marseille, south-eastern France. Fish species were distributed according to depth, with juveniles and small individuals being found in shallow waters, whereas larger individuals were found in deeper waters. However, depth by itself was not a significant factor in explaining fish species pattern, whereas sandy bottom habitat was significant. The most significant factors explaining fish species distribution were small and large blocks, and rock cover. Juvenile labrids, such as the most abundant ones Coris julis and Symphodus ocellatus, were only rarely observed deeper than 10 m, and the distribution of these juveniles was mainly correlated with a cover of macroalgae, rubble and small blocks. Fish density and fish biomass were higher in shallow than in deeper waters, although some species displayed an opposite pattern, such as the adult of C. julis and Diplodus sargus. The most significant factors explaining the fish density pattern found were the presence of macroalgae, Posidonia oceanica sea grass and sand cover. Among environmental factors assessed in this study, exposure to dominant winds was never significant, either for the whole fish assemblage or for juvenile labrids, or for the communities at any of the depth strata investigated. Depth was a significant factor influencing the distribution of juvenile labrids, whereas its significance in explaining fish density was lower. Bottom slope was generally more significant than depth, and thus constituted the most significant environmental factor. Benthic habitat characteristics were all significant, except for rubble cover, in explaining both fish species and fish density distributions. However, the amplitude of the relationships between substrate variables and fish assemblages was dependent on the descriptor studied (i.e. species distribution, including considerations of fish sizes, and fish density), suggesting that extrapolation of a particular relationship to other components of a fish assemblage would most likely be unfounded. Our results as a whole indicate that benthic habitat use by fish on Mediterranean rocky infralittoral coast is clearly non-random, and suggest that differences in habitat and/or environmental characteristics have significant effects at a small spatial scale on these fish assemblages.

Portuguese sole, Synaptura lusitanica, were collected from the Portuguese coast, between April 2001 and March 2002, to examine feeding habits, age and growth, and sexual cycle. Synaptura lusitanica fed on few prey items, its diet mainly composed of polychaeta, bivalvia and cephalochordata. Significant differences were found between the proportion of prey items according to season, length class of fish and coastal area. The main differences related to fish size were the higher ingestion of bivalvia by larger fish, in the west coast area, and the increase in the important cephalochordata for fish larger than 300 mm total length, in the south coastal areas. Polychaeta presented a lower importance in the spring–summer period while bivalvia increased its values in the autumn–winter period. Cephalochordata were more important in the autumn–winter period, but only for fish larger than 300 mm total length and in the south coastal areas. Vacuity was extremely high (mean value of 52%). Ages of S. lusitanica were determined from sagittae otoliths. The length of fish analysed varied from 157 mm to 480 mm, and the oldest fish was age 8. The von Bertalanffy growth equation parameters differed little between sexes, being the asymptotic length obtained for females higher compared to males. The highest values of the gonadosomatic index were obtained in summer, which was the period when the highest percentage of individuals in the spawning stage were recorded. Therefore, the spawning season seems to be from mid-spring (May) until the end of summer (September).

This paper describes the responses of a squid (Alloteuthis subulata) and a fish (Trachurus trachurus) to changes in the angular distribution of light.  An apparatus was made that simulated the angular distribution of daylight in the sea. The apparatus enabled the direction of the brightest light to be changed and the positions of the animals in response to these changes were observed. Squid viewed head-on were observed to roll by a maximum of 20° when the incident light source was at angles between 20° and 90° (where 0° is vertically downwards). When viewed laterally, i.e. in the pitch plane, the squid were observed to position themselves more closely with respect to the angle of the light source, they swam in a near vertical plane when the incident light source was at an angle of 90°. Swimming movements in the roll and pitch plane became more horizontal with positions of the light source between 90 and 180°. Horse mackerel, in contrast, inclined their dorsal surfaces to almost perfectly match the angle of the incident light source, even swimming upside-down when light came from below. These experiments also revealed that squid display a counter-shading chromatophore pattern (‘Flexible Countershading’) in response to light coming from the sides, which involves darkening the side of the body facing the brightest light. The use of chromatophores in this way may explain why the dorsal light reflex in squid is so weak compared to that of fish.

This study investigates the catch components of a commercially used demersal trawl cod end in Izmir Bay, and reveals some of the morphological characteristics of nine commercial fish species; red mullet (Mullus barbatus), hake (Merluccius merluccius), whiting (Merlangius merlangus euxinus), poor cod (Trisopterus minutus capelanus), tub gurnard (Trigla lucerna), common pandora (Pagellus erythrinus), axillary sea bream (Pagellus acarne), picarel (Spicara smaris) and annular sea bream (Diplodus annularis) in relation to mesh size and shapes. Furthermore selectivity of 40-mm polyethylene netting cod end for red mullet, hake, common pandora, axillary sea bream, picarel and annular sea bream is presented. The results are discussed in a way to understand the probable effects of fish body shape on mesh selectivity.

The morphology and growth pattern of male and female blue mussels (Mytilus edulis) from the north Norfolk coast, UK, were studied. In allometric terms, the external shell parameters of females grew faster relative to shell length than those of males. In absolute terms, females also grew more quickly than males for all external shell parameters and for most internal body parts. At a given age, females are therefore larger than males. Females had a higher shell to tissue weight ratio and a relatively heavier foot than males. A discriminant function incorporating age, weight and shell length, width, and height correctly sexed 81% of individuals in the sample from which it was derived. Both natural and sexual selection may be involved in the evolution of sexual dimorphism in blue mussels.

Fifteen individuals of four marine fish species (Torpedo marmorata, Raja clavata, Scorpaena porcus and Scorpaena scrofa) caught in the Dardanelles, Turkey, were examined for the leech Pontobdella muricata and Trachelobdella lubrica; 18 P. muricata and 23 T. lubrica were found on gills, at the base of the fins, and abdomen on 14 of the 15 fish.

Retained catches of trawl fleet in Chalkis fishing port-market, Greece, were analysed using generalized linear models (GLMs) in an attempt to identify factors that influence the total landings of the groundfish fisheries. Main effects in the model included a factor for vessel tonnage that determined fishing power, as well as factors for month and fishing area. Covariates examined were all found to have a significant effect on the retained catches, with month and vessel capacity alone explaining 38% and 30% respectively of the total variation of the data. Significant interactions observed indicate that the fluctuations in retained catch differed by fishing area and month as well as by fishing area and vessel category. Within vessel categories, month and fishing area also had significant effects on the retained catches, with fishing area being more important than month for the smallest vessels. Results indicate that the modelling approach of retained catches from trawl fisheries is a promising method for obtaining representative abundance indices.

Mussel seed Mytilus galloprovincialis from two origins (rocky shore and collector ropes) was cultivated on a raft (submerged culture) in the Ría de Arousa (north-west Spain) from approximately 20 mm to 60 mm shell length. Absorption efficiencies (AEs) and absorption rates (ARs) of the individuals were recorded in situ throughout cultivation time from November to July (1995–1996). Absorption efficiencies varied according to a multiple model that highlighted the significant effect of quality of natural seston (f as relative organic content), time of culture and origin of mussel seed. Initial AE values were 42 and 34% of the ingested organic material for collector ropes and rocky shore mussels (P<0.01), respectively. These differences remained significant for the first two months of the culture with higher values for collector ropes mussels. A significant relationship AE vs quality of natural seston (f) was observed according to an asymptotic equation: AE=0.82[1[minus sign]e−5.01(f−0.21)] for both sources of seed (r2=0.90). Absorption rate (mg organic matter g−1 h−1) followed a seasonal pattern with low values in winter and higher values in spring–summer as a consequence of better nutritional quality of food resources. Nevertheless, exceptional peaks of organic material from sedimentary origin in January caused an increase of ingested/absorbed organic material despite its low nutritional quality. Differences in AR values between origins of mussel seed referred to the first month under culture, with higher values for collector ropes individuals. Original habitat of mussel seed usually employed in mussel culture in Galicia is responsible for long-lasting effects through physiological changes that the individuals from the rocky shore habitat presented when placed under raft-submerged culture.

The responses to topical application of neurotransmitters to the mantle and fin muscles of the spear squid, Loligo bleekeri, were examined. In the mantle, the circular fibres contract in response to L-glutamate and the radial and longitudinal fibres contract in response to acetylcholine. 5-hydroxytryptamine (5-HT) did not affect contractions of any of the mantle muscle fibres.  The structure of the fin is similar to that of the mantle, with muscles arranged in three orthogonal planes. Topically applied L-glutamate causes all three muscle types to contract. Acetylcholine does not affect them. Pre-treatment with 5-HT blocks the L-glutamate response of the transverse and dorso-ventral muscles but has no effect on the longitudinal fibres. These results suggest that a secondary innervation pathway exists in musculature responsible for producing complex movements, such as the fin, but not in those with a simpler mode of action, like the mantle.

Polychaete prey were studied in the diet of 16 demersal fish species caught during an evaluation survey of demersal resources in the southern part of the Bay of Biscay during autumn, year 2000. A total of 27 prey taxa belonging to 17 families (21 of them at the species level) were found. Mullus surmuletus appeared as the main polychaete specialist. The consumption of polychaetes in other species, such as Pagrus pagrus, Chelidonichthys obscurus, Raja montagui, Scyliorhinus canicula, Trachyscorpia cristulata equinata and Pagellus acarne, was also important. Four species were analysed in more detail, M. surmuletus that preyed mainly on the families Nephtyidae, Sigalionidae and Goniadidae, P. acarne on Sigalionidae, R. montagui, on Sigalionidae, Arabellidae, Glyceridae and Aphroditidae, and S. canicula on Arenicolidae, Nephtyidae and Arabellidae. The most frequent species found in the stomachs were Nephtys hombergii, Aponuphis bilineata, Labioleanira yhleni, Arabella iricolor and Laetmonice filicornis. The predators had a clear preference for errant and carnivorous polychaete species, probably due to the more active behaviour of these prey, and also as a result of trawl fishing.