The free-running locomotor activity rhythms of freshly-captured swimming crabs Liocarcinus holsatus and L. depurator have been studied in constant conditions in the laboratory. L. holsatus captured in the intertidal zone of sandy beaches showed strong circatidal activity rhythms with maximum activity at high tide. L. holsatus captured in the sublittoral zone had a clear tendency to show circadian activity rhythms with highest activity during day-time hours. L. depurator occurred only sublittorally and showed circadian activity patterns with highest activity during the night. Exposure to hydrostatic pressure cycles of tidal amplitude and periodicity, entrained strong circatidal activity rhythms in previously arhythmic L. holsatus. This activity pattern also showed a marked circadian component. Exposure to the same regime entrained a circadian rhythm, but not a circatidal rhythm in L. depurator. In the sublittoral zone L. depurator is active mainly during the night, whereas L. holsatus, is active mainly during the day. This may constitute a behavioural mechanism for minimizing competitive interactions between these two sympatric crabs.

Based on qualitative data on prosobranch gastropods present at eight seamounts and islands of the Vitória-Trindade Seamount Chain off the eastern coast of Brazil, similarities at the species level are examined, and the effects of selection for different modes of development varying with increasing distance from the coast are investigated. Number of species decreases significantly from the continent towards easternmost localities. Similarity coefficients and cluster analysis suggest that similarities are greater among the western seamounts, followed by the eastern, most oceanic localities. Subtidal stations on Trindade Island show less similarity at specific level when compared with the remaining sublittoral stations. Percentages and absolute numbers of species with intracapsular metamorphosis decrease rapidly away from the coast in the sublittoral localities. However, there is little variation for the ratio planktotrophs/lecithotrophs among these localities, and their percentages remained constant over the entire Chain. In spite of the slightly wider range of distribution of planktotrophs within the Chain, the observations suggest that both planktotrophs and lecithotrophs can be effectively dispersed, probably by passive larval transport, in an ‘island-hopping’ pattern across the relatively small distances (100–250 km) that separate summits in the Chain. Notwithstanding shallow, subtidal conditions and intense isolation, percentages of planktotrophs and lecithotrophs also do not vary at the subtidal Trindade stations.

To evaluate the relative importance of tentacular crown and body surface in sabellid respiration, experiments were carried out on Eudistylia vancouveri (Kinberg, 1867), a long narrow worm living in a permanent tube in the intertidal zone. This species irrigates its tube by peristaltic waves, as do most species of Sabellinae and this allows water circulation inside the tube for body surface respiration.

Measurements of oxygen uptake after amputation of the tentacular crown indicated a reduction of about 80% of the total respiration. This value was higher than that found for other Sabellinae studied. Some predictions about other species were made on the basis of the present observations and of comparison with species having similar aptitudes.

The habit of living in a narrow tube protruding from the sea bottom, as occurs among sabellids, implies some adaptations concerning feeding, excretion and respiration. In the order Sabellida, the prostomium is reduced and fused to the peristomium which usually forms a large tentacular crown (Fauchald, 1977) with both feeding and respiratory functions. Its relative importance in respiration, however, is still little known. Survival after crown amputation suggests that this structure is not essential for respiration; moreover some species can autotomize and regenerate it (Berrill, 1931; Okada, 1934). In sabellids, respiration can in fact occur at the level of the body surface and this is made possible by the flux of the water contained in the tube which is generated by the worm itself: i.e. irrigation. Sabellinae species can actively irrigate their tubes by waves of muscular contraction of the body wall in either direction.

Thyasira gouldi, an arctic bivalve mollusc of the family Thyasiridae, has symbiotic, probably chemoautotrophic, bacteria living in its gills. In specimens collected from Loch Etive in Scotland in 1989, after the local population had undergone an unexplained decline, the gill bacteria contained numerous virus-like particles 60 nm in diameter. The bacteria are not lysed by the virus, and the particles are not present outside the bacteria except in phagocytic vacuoles of the gill cells where the bacteria have been digested, leaving the virus particles unchanged. Similar particles have been discovered in bacterial symbionts of Thyasira flexuosa, but in much smaller numbers.

The presence of Stoloteuthis leucoptera in the Mediterranean is recorded on the basis of three specimens, including an adult male, caught by IKMT and by commercial otter-trawl in the Ligurian Sea. The hypothesis of a recent immigration is discussed.

The list of Mediterranean cephalopods (Mangold Wirz, 1963; Torchio, 1968; Bello, 1986; Mangold & Boletzsky, 1987) includes the Sepiolidae of the subfamily Heteroteuthinae, whose members are supposed to be pelagic throughout their life cycle. Mangold Wirz (1963) recognizes in the Mediterranean fauna the unique species Heteroteuthis dispar, the other authors include H. atlantis Voss, which Voss himself (1955) reported at Messina. To this group may now be added Stoloteuthis leucoptera (Verrill, 1878) a species until now recorded in limited Atlantic areas. Verrill (1881) wrote “This species is an exceedingly beautiful one, when living, owing to the elegance and brilliancy of its colours and the gracefulness of its movements. In swimming it moves its fins in a manner analogous to the motion of the wings of a butterfly.”

Veliger larvae of the nudibranch mollusc Adalaria proxima are triggered to metamorphose to the benthic form by the adult prey bryozoan, Electro pilosa. Ion substitution and supplementation experiments with artificial sea water (ASW) have, however, shown that metamorphosis can be induced by elevation of the potassium ion concentration alone. Approximately 19 mM K+ASW (10 mM ‘excess’) was found to elicit maximal metamorphic responses: 29 and 39 mM K+ASW had no inductive effect. Choline chloride was also found to induce metamorphosis in a dose-dependent manner, with lO M ineffective, 10 M approximately threshold, and 5×10 M to 10 M optimal. Concentrations of choline >10 M were sub-lethally toxic. That the absence of larval metamorphosis on exposure to 29 and 39 mM K ASW was due to inhibition is inferred from interaction experiments with choline: at these concentrations of K, metamorphosis in response to choline could be abolished. Timed-exposure experiments indicated that artificial induction elicited by elevated K and choline involve either separate mechanisms, or different parts of the same pathway. Thus, whilst larvae required to be continuously exposed to 19 mM K ASW in order to complete metamorphosis, those exposed to 10 M choline would subsequently complete development in normal ASW following only 1–2 h exposure to the inducer. Preliminary experiments failed to specify further the nature of the natural inducer, beyond the confirmation that live intact colonies of the bryozoan Electro pilosa will trigger larvae to metamorphose.

Relationships between wet body weight, dry body weight and ash-free dry body weight (AFDW) were established for the aspidochirote sea cucumber Holothuria forskali (Echinodermata: Holothuroidea); a wetdry weight ratio of 6–38:1 was found. Length-weight relations were also determined. Low oxygen tensions and mechanical trauma induced H. forskali to eviscerate (70% of individuals tested). Respiratory measurements of intact and eviscerated sea cucumbers were determined at 17°C. For intact animals, oxygen consumption (ul h1) was directly related to AFDW (the slope of the regression line, b=0–60), whereas weight-specific oxygen consumption (Vo2; ul g1AFDW h) was inversely related to AFDW (b=0–54). Oxygen consumption of eviscerated sea cucumbers was independent of AFDW (b=0-\5), but Vo 2 was inversely related to AFDW (t–0–85). There were no significant differences between the respiratory rates of intact and eviscerated individuals, indicating that H. forskali is not so dependent upon respiratory trees for oxygen uptake as previously assumed.

Experiments on herring (Clupea harengus L.), sprat (Sprattus sprattus (L.)) and whiting (Merlangius merlangus (L.)) showed that when these fish make rapid swimming movements, such movements are preceded by fast pressure pulses in the surrounding sea water. Thefirst (a) phases of these pulses had durations of from 1–5 to 3–5 ms. The pulses could be excited in free-swimming fish by both visual and auditory stimuli and the latencies to the latter ranged from 5 to 8–5 ms. Identical pulses could be elicited by giving electrical stimuli to anaesthetized fish; these pulses had latencies from 34 to 7 ms.

The pressure fields around the fish were measured on suspended anaesthetized fish stimulated electrically. At any instant the fields of the fast pulses produced by whiting had the same polarity at all positions round the fish and pressure decayed inversely with the 1–5 powerof distance. The a phase of the fast pulse was usually a decompression.

The fields around a stimulated herring were different. The pressures on both sides oppositethe centre of the fish were of one polarity while those around the head and the tail were of the opposite polarity, the pattern of pressure being symmetrical about the long axis of the fish.In our experiments the a phase opposite the centre of the fish was always a compression. The amplitudes of these pulses declined with distance by the power of 2–5. In all species in our experiments the fast pulses were followed by slower pulses associated with swimming movements; these slower pulses had opposite polarities at corresponding points on the two sides of the fish.

Naturally spawned bass, Dicentrarchus labrax, eggs were incubated from fertilization at 15 temperatures from 6·8–20·6°C, and the developmental process was categorised into seven stages. Times from fertilization to the midpoints of each stage were calculated at each temperature. Knowledge of the developmental stage and incubation temperature was used to derive predictive relationships with which to age eggs. Minimum precision of age prediction was ±18 h. The first developmental stage was divided into six substages, and temperature-stage relationships derived to improve the precision of ageing to a minimum of ±1·75 h during early development. Bass eggs failed to hatch at temperatures below 9·7°C and above 16·8°C; this observation is discussed with reference to the developmental process.

Soleid eggs caught in the plankton off Algiers were reared and identified. Thus, the egg and the yolk sac stages of Microchirus ocellatus (L.) and M. azevia (Capello) were described, compared and differentiated from the corresponding stages of M. variegatus (Donovan). For the latter species, a large perivitelline space was often discernible.

In 1889, Cunningham referred some pelagic eggs caught near Eddystone (English Channel) to Solea variegata, owing to their similarity to the mature ovarian eggs of this species. Moreover, he considered the embryonic and larval stages described, illustrated and named ’species no. 1'by Raffaele (1888) as belonging to the same soleid. In further works, Cunningham studied the two-day-old larva (1890) and the newly hatched larva (1896). These papers and some others relating to Microchirus variegatus (Donovan, 1808) (present name of S. variegata) were reviewed by Ehrenbaum (1905), Padoa (1956), Nichols (1976) and Russell (1976).

Such eggs are often collected in the plankton of the Bay of Algiers, but I noted a great variability in their features. According to Quero et al.

The distribution and movements of intertidal butterfish Pholisgunnellus were studied on the westcoast of Scotland in relation to the foraging tactics of one of its major predators, the otter. Fish were individually tagged and released at low tide in restricted areas of 5 m wide running from the top of the shore towards the sea. Population density increased from 015 fish m" at the top of the shore to 1–1 fish nv in the Laminaria zone. The median total length of all fish examined was 92 mm (N=369) with a very distinct length class of 70–80 mm. There was no relationship between length and position on the shore. Only 24 out of 156 tagged fish were recaptured inside the restricted areas. The recaptured fish had moved a mean of 21 m (SD 1–9 m) in 1–6 days (SD 1–0 days), the directions of movement being randomly distributed. Repopulation rates were studied by removing all fish from three areas of approximately 180 m each. Fish of the same size moved into the cleared areas within two tidal cycles although in much smaller numbers (only 27–52% of the initial populations). Disturbance of the habitat probably played an important role because there was a general decline in numbers in regularly visited areas throughout the experiments. It is concluded that, even allowing for this disturbance intertidal butterfish are mobile and relatively unrestricted in their movements. From the point of view of predators like the otter and the heron, more butterfish are to be caught lower down the shore and each butterfish caught will soon be replaced by another of about the same size.

The fine structure of the flagellar root system of Isochrysis galbana Parke (Prymnesiophyta) has been investigated and a reconstruction is presented. Associated with the left basal body and arising close to the base of the haptonema there is a root composed of a ribbon of approximately five microtubules running peripherally towards the ventral side of the cell. Near the basal body it is also associated with two additional bundles of microtubules which diverge from it and from each other passing deep into the cell.

On the right-hand side of the right basal body there is a root consisting of four microtubules (2+2) which runs peripherally in a dorsal direction. Another root, consisting of a single microtubule only, originates close to the distal connecting band between the basal bodies, and passes around the ventral side of the left basal body before following a course deep into the cell. In addition, several fibrous bands connect the bases of the flagella and haptonema. The general arrangement of the root system of 1. galbana is comparable with many other members of the Prymnesiophyta, but attention is drawn to a number of important differences, particularly between Isochrysis and some other members of the order Isochrysidales. The results are discussed in the context of the evolution, phylogeny and taxonomy of the Prymnesiophyta.

On the right-hand side of the right basal body there is a root consisting of four microtubules (2+2) which runs peripherally in a dorsal direction. Another root, consisting of a single microtubule only, originates close to the distal connecting band between the basal bodies, and passes around the ventral side of the left basal body before following a curse deep into the cell.

Hyperbenthos was sampled at six stations on the western slope of the Norwegian Trough. Four hauls, two day and two night replicates were taken at each station. The replicates were analyzed based on all sampled individuals of Mysidacea and Decapoda Natantia using Shannon diversity index, Spearman rank correlation, G-test, Bray-Curtis similarity index and Correspondence Analysis. The sampler provided samples of mysids and shrimps with an acceptable level of replicability based on number of individuals and diversity. In a cost-efficient context it is satisfactory to take only one sample at a station.

There are four important influences on the temperature tolerance displayed by infaunal bivalves, namely their position on the shore, the depth to which they burrow, their geographical distribution and the seasonal cycle.

The temperature tolerance of a species is closely related to shore position and burrowing depth, since these both modify the actual range of temperatures to which the organism is exposed and the tidal variation in temperature. As one might expect, southern populations of a species tend to be lower on the shore than equivalents in northern Europe, but at any one location it is difficult to detect a difference in tolerance between individuals from the top of the shore and those from the bottom. Southern populations do have a higher tolerance to high temperatures than northern, despite the shift in littoral distribution. A similar pattern of response and shift in tolerance is shown between summer- and winter-acclimated specimens.

However, the seasonal shift in response to temperature is not entirely as might be expected, as oxygen consumption measurements show reverse acclimation (i.e. winter respiration rates lower than summer). Reverse acclimation has been demonstrated in a number of bivalve species, and the degree of reverse acclimation is here suggested to be related to the degree of deposit- or filter-feeding habit.

There is evidence that bivalves are capable of regulating to some extent their metabolic rate, independent of temperature. Six groups of Macoma balthica were investigated, of which the four from relatively high temperature environments regulated from 20°C, while the other two did not, suggesting that this capability can be acquired.

Species abundance data for benthic communities, collected during 1971–1988 off Northumberland on the north-east coast of England (western North Sea) and the Skagerrak (eastern North Sea), and pelagic data collected in corresponding areas during 1958–1988 by the Continuous Plankton Recorder (CPR) survey have been subjected tomulti-dimensional scaling ordination. Changes in community structure at the two benthic stations show a high degree of similarity, characterised by a transition in the late 70s. Similarly, there is a less marked transition between the 70s and 80s in pelagic community structure from the eastern North Sea but pelagic data from the western North Sea shows no discernible patterns. Benthic community biomass data, available only for the Skagerrak station, enabled abundance/biomass comparison curves to be constructed which demonstrated a change from un-disturbed communities in the early and mid 70s to moderately disturbed communities in the late 70s and 80s. North Sea macrofaunal abundance, and, in the Skagerrak, macrofaunal biomass appear to co-vary with phytoplankton colour and total zooplankton abundance, although there are insufficient data for statistical testing. A number of factors including eutrophication and/or pollution may be responsible for these changes in community structure.

Simple community parameters, such as number of species caught and the species diversity of a planktonic group (in this case Ostracoda), have been found to be stable enough in time and space to detect shifts in these parameters likely to be generated by interannual and decadal variation, especially if sampling is conducted at mesopelagic depths. At this time scale, changes in spatial variability will be expressed most clearly as shifts in zoogeographical boundaries. The clearest boundary to be detected in the North-east Atlantic occurs in the vicinity of 40°N, across which is a rapid equatorwards reduction in the total available nutrient as a result of a reduction in the depth of the mixed layer in winter. The boundary at 40°N is marked in satellite images by a sharp reduction in seasonality of surface chlorophyll concentrations. In the planktonic ostracods there is a sharp decline in both species numbers and diversity on the poleward side to a depth of at least 2000 m. If these changes are related to the degree of seasonality in the production cycle, then they can be expected to be climatically controlled. Monitoring this boundary will give an unambiguous signal of any future climate change, natural or anthropogenic, having a significant biological impact on the oceanic ecosystem and on fluxes of material within the water column.

Each summer, in the oceanic north-east Atlantic, a drop in the catch of albacore (Thunnus alalunga Bonnaterre, 1788) is observed for 8 to 10 days at the beginning of August. This temporary decrease of catch per unit effort (CPUE) is related to a relaxation of wind for 5 to 8 days during the previous 8 to 15 days. A similar and significant relationship is also observed in the Atlantic sardine (Sardina pilchardus Walbaum) fishery in a coastal area in the north-east of the Bay of Biscay (France). This indicates that a general ecological process is involved in this relationship between wind and CPUE of two pelagic fish, caught at the sea surface.

The timing of the response of the sardine and the albacore fishery to a relaxation of wind is interpreted in the light of a productivity model. The lack of wind-driven turbulent mixing provides a progressive decrease of the food organisms in the surface layer about 7 days after the wind event. Thus, fish disperse and become less susceptible to capture.

However, particular fertilization processes are involved at the continental shelf-break and the results of the association analysis were not found to be significant for the albacore fishery in this area.

The use of Superposed Epoch Analysis seems to provide a suitable method to analyse such a relationship with a daily time scale.

Comparison of the results of cross correlation analysis used in a previous work with a Superposed Epoch Analysis suggests that further considerations should be given to the use of the latter method infishery science.

Statistical methods for analysing changes in community structure fall under the three general headings of univariate, graphical/distributional and multivariate. These methods are applied to a variety of benthic community data (macrobenthos, meiobenthos, corals, demersal fish), from a variety of localities (intertidal/subtidal, temperate/tropical) and over both spatial and temporal scales. Four general conclusions emerge from this comparative study:

(1) The similarity between sites or times based on their univariate or graphical/distributional properties is usually different from their clustering in multivariate analyses.

(2) Species dependent (multivariate) methods are much more sensitive than species independent (univariate and graphical/distributional) methods in discriminating between sites or times.

(3) In examples where more than one component of the fauna has been studied, univariate and graphical/distributional methods may give different results for different components, whereas multivariate methods tend to give the same results.

(4) By matching multivariate ordinations from subsets of environmental data to an ordination of faunistic data, the key environmental variables responsible for community change may be identified.