Results from the Continuous Plankton Recorder survey were used to study long-term changes in the zooplankton of four regularly sampled areas of the North Sea. The trends in α-diversity are described and analysed. Species associated with inflow of oceanic or mixed waters from the Atlantic or shelf to the west and south of Britain have increased in abundance or frequency of occurrence. Meroplankton have also increased but resident holoplankton and those associated with colder oceanic or mixed waters have declined. These changes have resulted in an increase in the species richness in the areas in the north-western North Sea. There was a period of low diversity in the late 1970s and early 1980s in the most southerly area, furthest from the sources of inflow. The evidence for a long-term trend was stronger than relationships between diversity and either the North Atlantic Oscillation or variation in position of the Gulf Stream in the western Atlantic.

Vegetative annual cycle and primary production were described in the sea grass Posidonia oceanica in competition with two Ulvophycea, Caulerpa taxifolia (Cap Martin, France) and Caulerpa racemosa (Antignano, Italy). Sampling was performed at three stations exhibiting increasing levels of interaction with Caulerpa. Significant differences were observed as a function of the Caulerpa species, season and level of interaction. For each interaction, the different parameters have some seasonal variations. Any effects of the two Caulerpa species has been detected on the seasonal variability of our parameters. For all seasons, with increasing levels of interaction, the P. oceanica adult and intermediate leaf lengths, leaf index and mean age of the leaves always decrease whereas percentage of leaves having lost their apices, epiphyte biomass per unit surface area, mean number of leaves produced per shoot and per year always increase. Conversely, mean number of leaves per shoot or below-ground tissue production do not seem to be affected by Caulerpa. Finally, primary production of P. oceanica, by an increased turnover of the foliar tissues, was greater in the case of high interaction.

Marine representatives of the phylum Gastrotricha are reported for the first time from the State of New Jersey, USA. Littoral and shallow sublittoral sediment collected at Ship Bottom on Long Beach Island, near Atlantic City, yielded 11 species belonging to eight genera in six families in the orders Macrodasyida (four genera in three families) and Chaetonotida (four genera in three families). Littoral samples were richer than the one sublittoral sample (7 vs 4 spp.). Among the taxa was a large, undescribed species of Tetranchyroderma characterized by the following key traits: total body length up to 605 μm; cuticular covering complete, made up of pentancres; a pair of cephalic tentacles; dorsal adhesive tubes arranged in dorsal and dorsolateral columns; a pair of ventral adhesive tubes arising from a common base, near the perigenital area only on the right side; peculiar cuticular openings ‘stomata’ along the ventrolateral margins of the body; protogynous hermaphroditism. Tetranchyroderma weissi sp. nov. is, at least in the investigated location, restricted to the sediment layers below 20 cm of the intertidal zone, and is able to live in thiobiotic sediment. A key to the described species of the world based on easily discernible traits, visible in both living and formalin-fixed specimens is provided.

The short-term response of Mediterranean upper infralittoral macroalgal species to experimental human trampling was investigated. Disturbances of six different intensities were applied within the integral reserve of the Ustica Island marine protected area (Italy, Mediterranean Sea). The dominant macroalgal species Cystoseira brachicarpa v. balearica and Dictyota mediterranea were strongly affected by human trampling. Higher levels of disturbance significantly affected both algal percentage cover and canopy at an increasing rate. Three months after trampling, for both variables it was highlighted that the algal recovery from disturbance was incomplete, being significantly different among trampling intensities. The current study revealed that in the short-term it was not possible to identify critical levels of trampling that are sustainable for this shallow community.

The small free-swimming scallops, Chlamys hastata and Chlamys rubida, are frequently encrusted by the sponges Mycale adhaerens and Myxilla incrustans. It is unclear why this association exists. We hypothesized that living on scallop valves increases sponge survival by reducing the effects of sediment accumulation. Scallops were collected to measure correlations between sediment load and encrusting sponge mass. In the laboratory, the survival of sponges on living scallops and empty scallop valves was measured. Time-lapse video was used to quantify spontaneous swimming and clapping of C. hastata. In the field, both scallop size and sponge mass were significantly greater in high turbidity sites. In the laboratory, sponges on empty scallop valves experienced near complete mortality after five weeks. Manually clearing sediments increased survival but did not duplicate the high survival of sponges on living scallops, which regularly swam or clapped their valves.

A geographic discrepancy between the distribution boundaries for larvae and adults of the chaetopterid Mesochaetopterus sagittarius was recorded. The most northerly position where benthic individuals, probably not reproductive, have been collected in the Atlantic corresponds to the latitude of Aveiro (Portugal). The most northerly position for larvae corresponds to that of Arcachon (France). The larvae found off Arcachon constitute an influx of subtropical origin. They rarely succeed in passing the fixation stage, and when they do, the benthic stage is not capable of reproduction. The occupation of a very large zone by planktonic larvae spread over 4° of latitude (500 km), eventually resulting in sterile benthic populations, confirms that environmental constraints are less severe on larvae than on adults. This work emphasizes, through the integration of different oceanographic disciplines, the importance of knowing the structure of the spatial distribution of adults when seeking to achieve a better understanding of local recruitment.

A description of the midgut gland of Gammarus locusta with the aim of using this organ as a complementary tool in ecotoxicological studies was made. The hepatopancreas is composed of two pairs of blind-ending tubular structures. The thickness and length of these tubules were ∼50 μm and 5 mm, respectively, in adult males (10–12 mm length). The distal part of each tubule is characterized by non-vacuolated E-cells typically exhibiting a relatively high nuclear to cytoplasmatic ratio. The epithelium of the remaining tubules is characterized by abundant columnar R- and F-cells, both ∼40 μm long. Large vacuolated B-cells (∼60 μm length) were very common along the midgut gland but seemed to increase in number in the proximal region of each tubule. An SEM examination revealed a delicate network of muscle fibres that limits the organ.

This work is an interpretation of a chronological data set on abundances of estuarine soft substrate invertebrates using an ecological approach. The data were collected in the framework of the European programme COST 647 (Coopération Scientifique et Technique) on coastal benthic ecology which terminated in 1992. Species numbers and selected environmental factors were recorded at two stations in the Baie de Somme (France) from 1981 to 1992. Inter-annual and seasonal variations in benthos numbers were analysed using a plotting procedure based on a non-probabilistic approach, proposed by Andrews in 1972. Ecological groups of species were identified and succession in time described, coinciding with alterations in the landings of cockles Cerastoderma edule. The chronological data set was processed through the application of the cumulated function, giving directly intensity and duration of any changes in relation to the climate and water quality, especially potential eutrophication manifestations.

Macro and meiobenthic communities of two fishing areas (Vilamoura and Lagos) in the western part of south Portugal (Algarve coast) were analysed. Both locations had been under severe dredge-fishing impact until four years previously. Vilamoura has since continued to be dredged, while fishing activity in Lagos was stopped in 1995 as a response to overfishing. For each location, three replicate areas were analysed at depths of 7–9 m. In each of these areas, 18 quadrats for macrofauna and 12 cores for meiofauna were randomly sampled by SCUBA divers during September 1999. The Shannon–Weiner diversity index was higher for meiofauna in the fished area, whereas macrofauna diversity was higher in the recently non-fished area. Bray–Curtis dissimilarity between the two areas was 87·82%. Major differences were found between Ampeliscidea, Amphiura mediterranea, Spisula solida, Haustoriidae, Nemertinea and Diogenes pugilator populations at the two sites. There was higher abundance but lower biomass of potential macrofaunal scavengers in the fished area, and carnivore biomass was also higher in this area. Deposit-feeders dominated meiofauna abundance in both study areas. The community structure of the continuously fished area was dominated by small, opportunistic, short-lived species while the community structure of the recently non-fished area was dominated by more fragile and long-living sessile organisms.

A new species of Hydroides (Polychaeta: Serpulidae), is described. Thirty specimens of Hydroides tenhovei sp. nov. were found on a flat PVC structure on soft-bottoms near Punta San Juanico and five additional specimens from Cabo San Lázaro, Baja California Sur, Mexico. The new species is characterized by the presence of a verticil with three large dorsal hammer-shaped spines, partially fused; basal internal spinules are absent in these spines; other spines curve outwards, with sharp tips and a basal internal spinule.

Baited traps deployed at 7800 m in the Atacama Trench off northern Chile, captured over 400 specimens of Eurythenes gryllus. This is the greatest depth of occurrence reported for the species. Of the 398 specimens available for study, all but three were female, giving a sex ratio very different from any reported previously. Female specimens measured 29–76 mm in length, and all were immature. Length/frequency distributions based on total length, peraeonite 1 length, and coxa 4 oostegite length were unimodal. Relationships between total length, and peraeonite 1 length, oostegite length, and wet weight were established. Oostegite development appeared to be precocious compared with published data. Subtle differences in peraeon, urosome, gnathopods, coxa 4, peraeopod 7, and epimeron 3 morphology, and the growth of oostegites separate Atacama Trench specimens from previously described material. The morphology exhibited by these specimens lies outside the known variability of E. gryllus, and suggests that this pan-oceanic entity may be undergoing incipient speciation.

This study examined two types of muscle fibre, associated with entirely different tasks in the cyprid of Balanus amphitrite (Crustacea: Cirripedia), and detected a striking difference. The first fibre type is found in the antennulary system, which is used for selecting the most suitable substrate for continuance of the cirripede life cycle. The second fibre type is associated with the stereotyped swimming behaviour of the cyprid. The antennulary fibres have the characteristics of ‘slow’ fibres, whereas the thoracic fibres display the properties of ‘fast’ muscle fibres. The difference between the thoracic and antennulary muscles emphasizes the specialized morphology of the cirripede cyprid linked to their unique role in settlement.

A survey was carried out from April 1998 to June 2000 to study the structure and the secondary production of the population of Heteromastus filiformis in the Loire estuary. Each month, samples were collected in the intertidal zone of Mindin harbour. The length of the thorax (L12) was correlated with the fresh weight (FW) with the relation FW=1·49848 L12–3·62804 (r=0·92). In 1999, the mean density was 2184 ind m−2 with a minimum of 1104 ind m−2 in December and a maximum of 3328 ind m−2 in March. The mean annual biomass was 15·4 g m−2 with a minimum of 2·6 g m−2 in December and a maximum of 28·2 g m−2 in March. Most of the histograms of size–frequency are unimodal and could be considered a single cohort except in May and November/December 1999. The abundance and biomass of the population of H. filiformis decreased during summer and winter which are mortality periods and increase during spring and autumn which are recruitment periods for the population. The life time for a cohort was from six to nine months depending on the recruitment period and on the inter-annual variations. The secondary production was estimated by the method of Crisp (1971). The annual secondary production in 1999 was P=104·3 g m−2 with B¯=15·4 g m−2 and P:B¯=6·8. The quantity of sediment reworked by H. filiformis is about 116 l m−2 y−1 or 65 kg m−2 y−1 which is approximately a deep-sediment layer of 12 cm transported to the surface annually.

To assess the recovery of the lagoon in the Valle di Gorino, Italy, the macrobenthic assemblages were studied throughout a two year period, i.e. before and after the opening of a floodgate. Three stations were located along a gradient of confinement, and sampled for macrofauna, water and sedimentary parameters. Analyses were performed through univariate and multivariate techniques. The macrobenthic assemblages were characterized by a small total number of species, strong dominance in number by a few of these species, and low diversity, but changes in community structure and composition were clearly recognizable. Significant negative correlations were found between macroalgae and macrobenthic community attributes. The altered hydrological regime due to the opening of the floodgate disrupted macroalgal cycles and altered the related macrofaunal successional dynamics: species linked to the macroalgal degradation phase became dominant throughout the Valle. After the intervention, all areas exhibited similar species composition and abundances, and appeared to be in a permanently disturbed condition. A rescaling of environmental conditions repositioned species roles in the community: those species which were typical of a certain phase of the former successional progression, were successively dominating the whole lagoon, irrespective of time and the estuarine gradient. After the intervention, the spatial and temporal distribution of macrobenthic taxa was under the control of factors linked to organic enrichment of the sediments.

Netted dogwhelks Nassarius reticulatus were offered standardized olfactory signals derived from flesh of: cod (Gadus morhua), starfish (Asterias rubens), shore crabs (Carcinus maenas), mussels (Mytilus edulis), periwinkles (Littorina littorea), dog whelks (Nucella lapillus) and netted dogwhelks. Nassarius reticulatus responded positively to all signals except the conspecific one. Positive responses to extracts were in the order (strongest to weakest): Gadus, Carcinus, Nucella, Mytilus, Asterias, Littorina. Starved Nassarius reticulatus buried in sand emerged rapidly to feed on crushed C. maenas, but remained buried when offered crushed conspecifics. These data confirmed the hypothesis that N. reticulatus would not respond positively to the smell of conspecific carrion, to avoid emerging from the substratum while neighbours were being predated. However, a second hypothesis, that strength of response to olfactory signal was proportional to taxonomic distance between N. reticulatus and the source of carrion was not supported by the data.

The sphaeromatid crustacean isopod genus Campecopea is revised, a new diagnosis given and the genus Anoplocopea Racovitza, 1907, is placed in synonymy; the type species Campecopea hirsuta is redescribed and Campecopea lusitanica comb. nov. is recorded from the Canary Islands and Azores. The four species of Campecopea differ from each other principally in the presence or absence of a prominent posteriorly directed dorsal process on the male pereonite 6, the ornamentation of the posterior pereonites, the shape of the uropods and also the fine details of the dactylus accessory spine (smooth or serrate).  The phylogenetic significance of dorsal process is re-evaluated here, and the character discussed in relation to Campecopea, Dynoides and Clianella, and several other sphaeromatid genera. It is regarded that the interpretation of this character as being of intrinsic generic merit has resulted in the over splitting of several genera and also the creation of paraphyletic genera. It is suggested that reappraisal of sphaeromatid generic characters in cladistic terms is a necessary first step in terms of establishing the monophyly of many sphaeromatid genera.

Measurement of the respiration of Nucula nitidosa and N. nucleus determined that N. nucleus had a respiration rate approximately a third greater than that of N. nitidosa, 215·28 and 135·64 μl O2 gdfw−1 h−1, respectively. This was calculated to be equivalent to a metabolic rate of 0·648 J individual−1 24 h−1 for N. nitidosa and 1·752 J individual−1 24 h−1 for N. nucleus. Estimation of the production of N. nucleus, from its respiration rate, revealed that for comparable populations, N. nucleus was approximately a third more productive than N. nitidosa, 30 kJ g dry flesh weight (dfw)−1 m−2 y−1 as opposed to 20 kJ gdfw−1 m−2 y−1. Examination of the Kleiber's constant (β) obtained for each species, demonstrated that for N. nitidosa β fell in the range 0·75–1 and that for N. nucleus β fell in the range 1–1·25. This suggests, in combination with other data, that N. nucleus adopts an ‘exploitative’ functional strategy as opposed to N. nitidosa, which can be regarded as adopting a ‘conservationist’ functional strategy.

Observations on the hypoxic tolerance of both N. nitidosa and N. nucleus revealed that N. nucleus had a hypoxic tolerance about twice that of N. nucleus. The mean survival time±standard error for N. nitidosa was 3·53±0·18 d in contrast to 7·72±0·21 d for N. nitidosa. The hypoxic tolerance of either species was not related to body size and was independent of any possible effects of starvation. These results are discussed with reference to their potential effects to determine the distribution of N. nitidosa and N. nucleus.

The relationship between body size and population growth rate λ has been studied in two species of opportunistic polychaetes, Dinophilus gyrociliatus and Ophryotrocha labronica, which colonize harbour environments. These species exhibit a semi-continuous iteroparous reproductive strategy, are phylogenetically closely-related but differ in body size and in some aspects of their sexuality. Ophryotrocha labronica is about 4 mm in body length, displays only slight sexual dimorphism and its sex ratio is biased towards the female sex in the ratio 2:1. Dinophilus gyrociliatus is about 1 mm in length, the males are extremely small and the sex ratio is strongly biased (3:1) in favour of the females. In spite of the considerable differences in all traits of their life histories and in many demographic parameters, the growth rates of the two populations are very similar. The analyses carried out have shown that the rapid attainment of sexual maturity of D. gyrociliatus gives it an advantage that offsets the greater fecundity of O. labronica. It is very likely that the reproductive peculiarities of D. gyrociliatus help to raise the population growth rates. The ‘saving’ on the male sex achieved both by the shift of the sex ratio in favour of the females and by the reduction in the males' body size would appear to enable D. gyrociliatus to grow at the same rate as O. labronica, a larger and more fecund species.

The behaviour of two ectosymbiotic animals, Peregrinamor ohshimai (a bivalve attached to the ventral cephalothorax of the host), and Phyllodurus sp. (a bopyrid isopod attached to the second pleopod of the host), during ecdyses of the host thalassinidean Upogebia shrimps was studied by time-lapse video of infested shrimps. In the intermoult stages of the hosts, both ectosymbionts did not move. However they moved on to the newly emerged body of the host at the time when the host moulted. Peregrinamor ohshimai began to move just after the host started moulting, whereas Phyllodurus sp. moved prior to ecdysis of the host and waited near the fissure from which the newly moulted body emerges first. There are highly correlated morphological relationships between the symbionts and the hosts. It is suggested that both ectosymbionts grow with the same host individuals after infection, keeping morphological affinity with their hosts without being discarded during ecdyses of the hosts.

The effect of algal food concentration, substratum, light, salinity, cyprid density and ‘footprints’, cyprid age, films of organic biopolymers, bacteria and diatoms on the settlement of Balanus reticulatus cyprids were studied. The algal food quantity (from 7×104 to 4×105 cells ml−1) fed to nauplii had a significant effect on the settlement. Cyprids failed to settle on glass surfaces but would settle on polystyrene. Light, cyprid ‘footprints’ and age significantly affected the settlement, however, salinity (from 20 to 40 psu) and cyprid density (from 5 to 200 per 5 ml of seawater) had no effect on the settlement. Films of organic polymers, bacteria, and diatoms inhibited the settlement compared to control. It is suggested that cyprids of B. reticulatus can serve as an appropriate test material for antifouling bioassays in those areas where the former forms a dominant species.