The lowest photon flux density of photosynthetically active radiation at which O2-evolving marine photolithotrophs appear to be able to grow is some 10 nmol photon m−2 s−1, while marine non-O2-evolvers can grow at 4 nmol photon m−2 s−1, in both cases with the photon flux density averaged over the 24 hour L:D cycle. Constraints on the ability to grow at very low fluxes of photosynthetically active radiation fall into three categories. Category one includes essential processes whose efficiency is independent of the rate of energy input, but whose catalysts show phylogenetic variation leading to different energy costs for a given process in different taxa, e.g. light-harvesting complexes, RUBISCO and probably in the sensitivity of PsII to photodamage. The second category comprises essential processes whose efficiency decreases with decreasing energy input rate as a result of back-reactions independent of the energy input rate, e.g. charge recombination following charge separation by PsII and short-circuit H+ fluxes across the thylakoid membrane which decrease the fraction of pumped H+ which can be used in adenosine diphosphate phosphorylation. Category two also includes that component of protein turnover which cannot be related to replacement of polypeptides which were incorrectly assembled following uncorrected errors of transcription or translation, or which were damaged by processes whose rate increases with increasing energy input rate such as photodamage to PsII. The third category includes only O2-dependent damage to the D1 protein of PsII whose rate increases with a decreasing incident flux of photosynthetically active radiation. Processes in categories two and three are most likely to impose the lower limit on the photon flux density which can support photolithotrophic growth. The available literature, mainly on organisms which are not adapted to growth at very low photon flux densities, suggests that three major limitations (charge recombination in PsII, H+ leakage and slippage, and protein turnover) can individually impose lower limits in excess of 20 nmol photon m−2 s−1 on photolithotrophic growth. Furthermore, these three limitations are interactive, so that considering all three processes acting in series leads to an even higher predicted lower photon flux density limit for photolithotrophic growth.

Beamtrawl samples were taken monthly between January 1988 and December 1989 in 14 subtidal stations along the longitudinal axis of the Westerschelde Estuary. The estuary harboured high densities of epibenthic species (total average of 2250 ind 1000 m−2). Only 37 fish species were recorded and three mobile macroinvertebrate species were quantified. Seventeen epibenthic species were common, only eight of which were very abundant. An overall dominance of the brown shrimp Crangon crangon was noted. The near absence of anadromous and freshwater species was correlated with the low oxygen concentrations upstream the Dutch–Belgian border. The epibenthic species could be divided into a polyhaline and a mesohaline community along the main salinity–oxygen–turbidity gradients of the estuary. The mesohaline zone was characterized by higher densities and biomasses for shrimps, gobies and flatfish. The spatial structure in the epibenthic community of the polyhaline zone was more influenced by the watermasses from the sea and inflowing channels, and was correlated with the degree of exposure (current velocities and tides). A classification is proposed, based on the season in which the epibenthic species occur in the estuary, and on their life stages and abundances during that period. The monthly data demonstrate that while the eight abundant epibenthic species were generally present throughout the year (summer or winter resident), the majority tended to appear in the Westerschelde at varying times (summer, winter or bimodal) and often remained in large numbers (nine common species) for only a short time. The fact that mainly juveniles were recorded in the higher density-classes, suggests that the Westerschelde Estuary still acts as a nursery area for many epibenthic species.

Protozooplankton growth was measured by incubation in a walk-in cooling room at 5°C of filtered seawater from six stations on a south–north transect from open water through drift ice and into fast ice in the central Barents Sea (72°30′N–76°32′N). Eight species of naked ciliates, two species of tintinnids, seven species of athecate dinoflagellates and nine species of thecate dinoflagellates grew in the 24 and 48 h bottle incubations. Maximum potential mean specific growth rates of 0.84, 0.59, 0.39 and 0.39 d−1, respectively, indicated a hierarchy in growth rates determined by taxonomic differences where growth of naked ciliates > tintinnids > athecate dinoflagellates > thecate dinoflagellates. The mean±SD in situ temperature (4 to −1.8°C) corrected growth rates (Q10=2.8) for the six stations (0.74±0.31, 0.74±0.16, 0.25±0.16, 0.23±0.27 d−1) also suggested a higher growth for ciliates in comparison to dinoflagellates. Additionally, it revealed that the naked ciliates responded to the increased food availability, whereas this was not the case for all other groups of protozooplankton.

Diversity and biomass of ciliates and heterotrophic dinoflagellates were analysed at six stations on a south–north transect (mimicking a time span of months in the biological succession during the Arctic spring–summer) from open water through drift ice and into fast ice (72°30′N 76°32′N) during spring 1993 in the open Barents Sea. A pycnocline was observed beneath the sea ice at 40–50 m. A diatom spring bloom beneath the ice with chlorophyll-a maximum >10 μg l−1 and a diverse protozoan community with a peak biomass of 34 μg C l−1 was associated with this bloom. Maximum biomass of tintinnids (1 μg C l−1), athecate dinoflagellates (8 μg C l−1) and thecate dinoflagellates (26 μg C l−1) were found associated with the chlorophyll-a maximum in the upper 10 m of the water column beneath the sea ice at the northern stations. In contrast, the protozooplankton community was dominated by naked ciliates at the southern open water stations. Here chlorophyll-a was low (<1 μg l−1) and the maximum biomass of protozooplankton was 10 μg C l−1 of which naked ciliates accounted for >50%.

Cell sizes and estimated carbon content of cells >11 μm, as well as depth by depth biomass of 12 species/types of naked ciliates, 12 tintinnids, 12 athecate dinoflagellates and 24 thecate dinoflagellates, are presented. The community of naked ciliates was dominated by Strombidium spp. and Strobilidium spp., the tintinnids were dominated by Parafavella spp., Ptychocylis, Leprotintinnus, Acanthostomella and Tintinnopsis. The very small gyro-/gymnodinoid cells and Gyrodinium cf. spirale dominated the athecate dinoflagellates and the thecate dinoflagellates by the heterotroph Protoperidinium spp. generally accounted for the major part of the protozooplankton biomass along the transect. The Margalef diversity index revealed lowest diversity of ciliates and heterotrophic dinoflagellates in the open water and higher at ice-associated stations. The overall diversity was coupled with prey availability in terms of food concentration, but already saturated at 0.1 μg chlorophyll-a l−1.

The polychaete family Polynoidae (scale-worms) is well-represented at deep sea hydrothermal vents. Most species are free-living in a wide range of habitats: from high-temperature hydrothermal `chimney' walls to diffuse venting areas. Conversely, species of the genus Branchipolynoe live inside the mantle cavity of vent and seep mytilids. Specimens, morphologically close to Branchipolynoe seepensis, have been reported from all the known vent areas on the Mid-Atlantic Ridge (MAR), with varying infestation rates (0–6 individuals per host). Reproductive tract, gametogenesis and population structures were examined for specimens from the Lucky Strike vent field (MAR) in order to test whether this species displays dwarf males, protandric hermaphroditism or differential mortality between males and females. Observations of histological sections reveal the presence of fully developed ovaries in females which originate ventrally in segments 7–9 and of an unusual genital tract in which both sperm and mature oocytes are stored. Oogenesis is intraovarian and quasi-continuous. The vitellogenic oocytes are only free in the coelom at their terminal growing stage and are then transferred into an ovisac through spermathecae. The species displays an external sexual dimorphism in the number of genital papillae and the shape of the pygidial appendages. Sex ratios showed significant deviations from a 1:1 expected ratio, in favour of females. The modal decompositions of size–frequency histograms show the occurrence of three modes in females and only two modes in males, indicating discrete breeding periods. The two first modes were not significantly different between males and females. These results indicate that B. seepensis forms heterosexual pairs and uses internal fertilization to reproduce during discrete spawning periods. Differential mortality between males and females is likely to shape size-histograms as observed by preventing males from reaching the female proportions. Such an observation could be a result of either cannibalism on larger males, small sizes facilitating the male escape, or natural predation when males move from one bivalve to another to breed.

Samples of four species of algae were collected from three mid-shore pools on each of three shores on the north-east coast of England in order to describe colour polymorphism in the common intertidal ostracod Paradoxostoma variabile. Eight different colour morphs were found within the populations. On all shores, male P. variabile occurred in significantly higher densities than did the females, and males exhibited a significantly higher colour morph diversity and colour morph richness than females. On two out of three shores, males showed a significant association in colour morph frequency with algal species (but the pattern was not consistent between shores), but no such association was found in the female populations. In either sex, colour morph diversity did not vary between algal species but samples of male ostracods from the shore at Holbeck contained a significantly higher diversity of colour morphs than samples from the other two shores. In the laboratory, neither sex demonstrated a specific association with algal species suggesting that habitat selection is not an important factor in maintaining colour morph frequencies in this species.

A subtidal population of the anomuran crab, Pisidia longicornis was sampled quantitatively throughout 1997. Divers, using SCUBA equipment, conducted suction sampling each month, with concentrated effort directed towards the settlement season. Pisidia occurred in very high densities, constituting the major component of decapod community abundance. Gravid females were detected between March and September. Newly settled megalopae were present in benthic samples from June until late September. Six distinct settlement events were detected during this period, with pulses coinciding with low spring tides. Body size at settlement decreased as temperature during larval development increased. The rapid growth of each distinct settlement group was followed over time through each subsequent crab stage up to maximum adult size. Growth was suspended between December and April. Survival within each distinct settlement group was density-independent during the first summer's growth. Mortality increased between June and July settlement events, with the rate of decline remaining a linear function.

The ovary structure of the hermit crab Diogenes pugilator (Crustacea: Decapoda), is described in the different phases using electron microscopy. Sexual maturity was reached at a very small size; females from 0.74 mm shield length (SL) could be found in vitellogenesis stage and even 0.6 mm SL ovigerous females exist. The biometric study of the ovigerous females by independent size-class (non-accumulative) shows that 1.3 mm SL is the size at which 50% of females are ovigerous; this value is increased a little (1.7–1.8 mm) if the population of females, or ovigerous females, is analysed from an accumulative point of view. In addition, an optimal reproductive size (between 2.1 and 2.3 mm SL) and a reproductive decrease in the maximum size-classes have been detected. The relation between brood size (measured through egg number) and the hermit crab size follows a potential function. The number of eggs by brood varies in a wide range (9–2838), with a mean diameter of 0.35±0.03 mm. No relationship between egg size and shield length has been found.

The diet of the spider crab, Maja squinado, was studied in the rocky subtidal areas of the Ría de Arousa (Galicia, north-west Spain), by analysing the gut contents of crabs caught in the summer and winter of 1992. The highly diverse diet was made up primarily of macroalgae and benthic invertebrates that were either sessile or had little mobility. The most important prey were the seaweeds Laminariaceae (43% of the frequency of occurrence and 15% of the food dry weight), Corallina spp. (38% and 3%), molluscs [the chiton Acanthochitona crinitus (15% and 1%), the gastropods Bittium sp. (30% and 2%), Trochiidae and others and the bivalve Mytilus sp. (32% and 12%)], echinoderms [the holothurian Aslia lefevrei (32% and 18%) and the echinoid Paracentrotus lividus (16% and 7%)] and solitary ascidians (18% and 6%). The variability in diet composition was determined by the season (Laminariaceae, Corallina spp., P. lividus, Mytilus sp., gastropods and chitons appeared in greater frequency in winter, while the solitary ascidians and A. lefevrei were consumed to a greater extent in summer) in addition to sexual maturity (prey such as Bittium sp. or Trochiidae were more common in juveniles). Moreover, the changes in the food consumption rate were linked primarily to the moult stage. Feeding activity plummeted during the phases immediately preceding and following ecdysis (stages D0–D3–4 and A), and the diet was less diverse during these phases. No feeding differences were found that could be linked to sex. The composition of the diet of Maja squinado appears to be determined by the seasonal abundance of the different prey in subtidal rocky areas and by their availability (depending on their behavioural and anatomical characteristics, mainly mobility and the presence of hard external structures). Moreover, life history factors have little importance in the variability of the diet composition and only the moult cycle has a considerable effect on feeding rate.

Comparative morphology of the cement delivery apparatus of three lepadomorph barnacles indicates that the lepadid Lepas anatifera is unable to relocate voluntarily, whereas the two scalpellids Pollicipes pollicipes and Capitulum mitella can. Mean relocation speeds of up to 50 μm d−1 were measured for both scalpellids, which are probably underestimates of maximal rates given the absence of a directed stimulus. In the laboratory neither gravity nor unidirectional flow proved effective stimuli in directing scalpellid relocation. The two scalpellid species use quite different mechanisms to effect relocation at a leading edge of the base, although both slough basal material at the trailing edge. It is suggested that basal growth effectively accounts for the mobility of P. pollicipes but C. mitella is likely to employ muscular activity.

Eicosanoids are oxygenated derivatives of C20 polyunsaturated fatty acids known to play key roles in many physiological events in both invertebrates and vertebrates. The eicosanoid generating capacity of cypris larvae of the barnacle, Balanus amphitrite, was examined using enzyme immunoassay and high-performance liquid chromatography. These larvae generated the lipoxygenase products, 12-hydroxyeicosapentaenoic acid (HEPE), 8-HEPE and 8,15-diHEPE, together with the cyclooxygenase products, prostaglandin (PG) E, PGF and thromboxane (TX) B. Indomethacin, a selective cyclooxygenase inhibitor, caused a dose-dependent inhibition of PGE generation by B. amphitrite larvae, while esculetin and nordihydroguaiaretic acid (lipoxygenase inhibitors) also strongly inhibited the generation of 8-HEPE, 12-HEPE and 8,15-diHEPE. PGE2, PGE3 and 16,16-dimethyl PGE2 caused a dose-dependent inhibition of settlement of B. amphitrite larvae while indomethacin (25–100 μM) stimulated this process. Lipoxygenase products (8-HEPE, 12-HEPE and 8,15-diHEPE) as well as esculetin and nordihydroguaiaretic acid (10–100 μM) had no effect on the attachment of larvae.

Temporal evolution of the ingestion and absorption rates of organic matter and biochemical components in the filter-feeding bivalve Cerastoderma edule (Mollusca: Bivalvia) fed for 12 d on the same ration (1.5 mm3 l−1) of the microalgae Tetraselmis suecica (Chlorophyta: Prasinophiceae) having different biochemical composition, were measured. Cockles in group E were fed algal cells harvested at the exponential growth phase (55.5% of protein, 16.8% of carbohydrate and 27.6% of lipids) whereas cockles in group S were fed cells harvested at the stationary growth phase (45.3% of protein, 35.2% of carbohydrate and 20.0% of lipids). After the feeding period cockles were submitted to starvation and biochemical analysis of faeces produced during final steps of gut evacuation (after 24–96 h of starvation) was performed to estimate biochemical composition of metabolic faecal losses (endogenous matter lost during the process of digestion).

Ingestion rate of organic matter was found to gradually increase during the feeding period in both groups. Absorption efficiency of organic matter decreased but reached an asymptotic minimum with rising ingestion rate. This relationship resulted in a gradual enhancement of absorption rate of organic matter over the time. Lipid fraction of food was found to be absorbed with significantly lower efficiency (even negative values were recorded in group S) than proteins and carbohydrates irrespective of the diet. Endogenous faecal losses presented high proportion of lipids (up to 66%) and lower proportions of proteins (∼25%) and carbohydrates (∼9%). On the other hand, increasing carbohydrate abundance in the diet brought about no apparent enhancement of carbohydrates absorption efficiency. Results are discussed in relation to the time-course of digestive enzyme activities.

The distribution and relative abundance of macroepibenthic echinoderms in the eastern English Channel and Irish Sea is described from beam trawl catches. Echinoderms accounted for approximately 29% (by biomass) of fauna captured. A total of 24 species were recorded, including 12 species of starfish. The most frequently encountered species were Asterias rubens and Psammechinus miliaris, which were recorded at 85.5% and 56.0% of stations respectively. Asterias rubens and Ophiothrix fragilis accounted for 63.7% and 25.5% (by biomass) respectively of the echinoderms sampled. Mean echinoderm catches ranged from 0.8-kg h−1 in the north-eastern English Channel to 329-kg h−1 in the south-eastern Irish Sea. The echinoderm fauna was more diverse in the St George's Channel and western Irish Sea (6.7–7.0 species haul−1) than in the north-eastern English Channel (1.9 species haul−1).

The dominant lipids of seven species of abyssal holothurians (Oneirophanta mutabilis, Pseudostichopus villosus, Psychropotes longicauda, Deima validium, Parariza prouhoi, Amperima rosea and Molpadia blakei) have been examined in detail. Fatty acid compositions are qualitatively similar to those of shallow-water holothurians, but relatively higher amounts of unsaturated compounds in the deep sea animals are ascribed to an adaptation of the latter to maintain membrane fluidity at high pressure and low temperature. The sterol distributions of abyssal holothurians are complex, with mixtures of C26–C30 sterols being present in all of the animals. These are most likely to be dietary in origin; the holothurians substitute Δ5 with Δ7 unsaturation, via Δ5,7 or Δ0 intermediates. 14α-methylcholest-9(11)-enol, which is a common product of de novo biosynthesis in shallow-water holothurians is absent in all of the deep-water species. Furthermore, cholest-7-enol, the dominant product of de novo biosynthesis in shallow water animals, is a relatively minor component in all of the species, except A. rosea. This holothurian is also the only one that appears to assimilate 4α-methylsterols directly and contains high amounts of steryl sulphates. There are significant interspecies differences in the free sterol distributions which may reflect their different feeding strategies or niches.

Age and growth of the snipefish was studied based on samples collected in the Portuguese continental waters between 1996 and 1998. Analysis was conducted for two species, Macrorhamphosus scolopax and M. gracilis and for both species combined. Total length ranged from 5.5 to 18.2 cm for M. scolopax and from 5.4 to 17.3 cm for M. gracilis. Length–weight relationships were described for M. scolopax (a=0.00401; b=3.127), M. gracilis (a=0.00459; b=3.006) and both combined (a=0.00240; b=3.282). Age estimation, based on otolith observations, resulted in six and five years maximum age attributed to M. scolopax and M. gracilis, respectively. Back-calculation analysis based on a polynomial relation of the otolith radius on total length provided significantly smaller lengths-at-age compared with observed lengths. The von Bertalanffy growth curves fitted to observed lengths-at-age provided parameters of L∞=15.7 cm, K=0.654, t0=−1.066 for M. scolopax; L∞=14.2 cm, K=0.694, t0=−0.954 for M. gracilis and L∞=15.8 cm, K=0.470, t0=−1.408 for both species combined.

The pit organs (free neuromasts) of sharks are part of the lateral line sensory system, but there is still confusion about their exact morphology and function(s). This is partly because of reported physiological differences between the pit organs and the lateral line canal neuromasts, and partly because the morphology of pit organs has not been adequately documented. To compare their morphology, the pit organs and canal neuromasts of the gummy shark Mustelus antarcticus (Chondrichthyes: Triakidae) were examined using transmission and scanning electron microscopy. Both pit organs and canal neuromasts had hair cells with the `staircase' arrangement of sensory hairs (stereovilli) characteristic of vertebrate mechanoreceptors. Stereovilli bundles of different sizes were distributed haphazardly throughout the pit organs and canal neuromasts. The density of hair cells was similar in the pit organs and canal neuromasts, but differences in the overall size and/or shape of the sensory epithelia might account for some of the reported differences in mechanosensitivity.

Fourier spectral analysis was used to highlight a rhythmic dimension of the click repetition pattern of the sperm whale (Physeter macrocephalus). Analysis of numerous series of regular clicks only showed occasionally the previously described codas used for communication. Out of a sample recording of vocalizing sperm whales, an apparent cacophony, belonging to a year-round resident group foraging a few miles off the coast of Gran Canaria, the individual click sequences of four animals have been unravelled by cross-correlating their time wave shapes.

The Fourier spectrum, which yields the harmonic aspects of each isolated click sequence, shows a deterministic structure that appears as a strong modulating frequency. This shows that click production is not a random process and possibly characterizes, in fact, a signature of the animal. Here we introduce a new concept: this rhythmic modulation represents the acoustic signature of each individual sperm whale, which we have called RIME (rhythmic identity measurement). The RIME would allow a whale to distinguish its own echo time pattern from the background of other click trains during echolocation. The RIME appears to represent a new concept in communication strategies and might also be present in other-social-odontocete repertoires.

A new hand-held corer for meiofaunal sampling and vertical profile investigation was developed. Its design and use prevents problems connected with core compression caused by the use of a plunger for core extrusion as generally applied in common coring techniques. This represents an advantage when meiofauna vertical profiles are investigated. A comparison between vertical profiles obtained from the newly developed corer and from commonly used corers shows that non-extrusive techniques significantly reduce sediment core compression.

Trigonioids represent the most plausible marine outgroup for freshwater palaeoheterodonts, yet details of their early ontogeny are scant. We utilized museum specimens and scanning electron microscopy to characterize the prodissoconch structure of the ‘living fossil’ Neotrigonia margaritacea. This species produces a large inflated prejuvenile shell (mean length ±SD=664±16.9 μm, N=8) that lacks both an umbone and a prodissoconch II. It is concluded that N. margaritacea does not rely on planktotrophy to fuel its prejuvenile ontogeny.

The first finding of the brittle star Amphiura securigera (Echinodermata: Ophiuroidea) in the Tyrrhenian Sea is reported. According to literature data, biotopic and edaphic features of the bottom indicate that this species preferentially lives in detritic mud-free biotopes characterized by good water circulation. Present data show that in the Mediterranean Sea A. securigera extends its bathymetric range as far as the circalittoral and upper bathyal floors.