The arrow crab Stenorhynchus seticornis (Brachyura, Majidae), is a common inhabitant of the rocky subtidal along the Brazilian coast. Fecundity and the influence of environmental variables on egg production are investigated in this study. Information on egg size and egg loss through incubation are also provided. Monthly samples were conducted using SCUBA diving, from January to December 1998 in the Ubatuba region (23°25′25[double prime or second]S–44°52′03[double prime or second]W), south-eastern Brazilian coast. Early broods were used for the estimation of size-specific relationships of fecundity. Egg loss was assessed by comparing average egg numbers of early and late broods. The fecundity was estimated in 621.1±339.6 eggs, with an average diameter of 0.48±0.1 and 0.57±0.1 mm for early and late eggs, respectively. The number of eggs produced was apparently constant year-round. No significant differences were recorded among monthly fecundity values. The variation of abiotic factors did not show any relationship with temporal variability of fecundity, suggesting that the environmental effect in egg production is slight at best.

Population structure and biology of Octopus vulgaris was investigated along the south-eastern coast of South Africa. Samples were collected inter- and sub-tidally as a precursor to the establishment of an experimental octopus fishery in the region. In total, 300 (intertidal) and 147 (subtidal) O. vulgaris were collected over a two year period. Females were found to dominate the intertidal area (sex ratio 2:1), while no difference was found subtidally (sex ratio 1:1). Of those collected intertidally, immature females were most prevalent while males ranged from immature to mature. Mature females were only found subtidally. A marked size difference was apparent, with the subtidal octopus being substantially larger. Although brooding females were found throughout the year, numbers peaked in summer. Individual fecundity ranged between 42,000–790,000 eggs. The total number of eggs produced and the number of eggs per egg string were correlated to female size. Diet did not vary greatly between the inter- and sub-tidal areas, with the main prey items being crustaceans, teleosts and octopus. It appears that the immature females use the intertidal area to feed and grow, before migrating to deeper areas to mature and spawn.

Excavation counts (absolute density), burrow counts and surface active individuals visual counts in a Uca tangeri population were compared. Population density estimated from burrow counts was not significantly different from population density estimated by excavation, but the population density estimated with visual counts was significantly lower than the absolute density. Ovigerous females should be the main cause of these differences because they frequently remain underground, but other groups of crabs are also contributing to this difference. Burrow counting is an accurate and quick non-invasive method for the census of U. tangeri. Other population measures (e.g. sex ratio) are not obtainable by burrow counting and only further understanding of the activity patterns of this species along the tide cycle, moon phase and reproductive season will allow visual counting of surface active individuals to be used as quick, efficient and non-invasive method for crab density and population structure estimation.

Seasonal variations in feeding physiology and scope for growth of green mussels Perna viridis (Bivalvia: Mytilidae) were investigated in Ma Wan, an estuarine mariculture site located in the southern waters of Hong Kong. Total particulate matter, particulate organic matter, particulate inorganic matter and organic fraction of seston (f), and food availability were monitored monthly from January to December 1998. Feeding rates, including clearance rate, filtration, ingestion and absorption, and absorption efficiency were higher in summer and autumn and lower in winter. Pseudofaeces were produced but the preferential selection of organic materials by P. viridis was not concluded. Scope for growth in  July and October were higher than in February. Activities of digestive enzymes including amylase and cellulase in the digestive diverticula and crystalline style were high in May and July and lower in February and October and correlated with f. Faster growth rates obtained for P. viridis in Hong Kong's summer are considered a result of enhanced feeding and absorption at high temperatures and f values.

The objectives of this study were to assess population biology and dynamics of the squat lobster Galathea intermedia. On the basis of nearly regular monthly samples taken with a 2-m beam trawl in the Helgoland trench (HTR) during the period of 1985 until 1992, sex ratio, length composition, relative growth and reproduction were studied. The overall sex ratio deviates significantly from 1:1 with 1[male ]:1·8[female] (P[les ]0·001). On average, sexes are equally large, but adult females attain a slightly larger size than adult males. No sex-specific differences in the length–weight relationship were found. Relative growth of the first abdominal segment is clearly of sexual-dimorphic character. On the basis of the length–frequency distributions, the life cycle of the HTR population lasts between one and two years. According to the appearance of ovigerous females and juveniles, reproduction and recruitment are clearly seasonal. Recruitment takes place between July and December. The main reproduction begins in April and ends in September, with a peak between June and August. A significant increase of specimens showing both male and female morphological characters, referred to as morphological hermaphrodites (P[les ]0·001), and males (P[les ]0·05) respectively, was detected.

A number of mangrove systems with associated tidal flats occur in Coiba Island, located off the Pacific coast of Panama, two of which were selected for the present study: Santa Cruz and El Gambute. Three transects were selected on each tidal flat and three sampling sites were arranged along each one: lower, middle and upper intertidal. During 1997, two samplings were carried out at each site, in February and November. The results of the faunistic studies revealed the presence of ten species of Orbiniidae, two of which belonged to the genus Leodamas. Leodamas minutus sp. nov. is easily distinguished from all other species within the genus by having a cylindrical thorax composed of 13 chaetigers, the first three chaetigers without notopodial lobes, thoracic neuropodia without postchaetal process, and abdominal neuropodia, short, bilobed and with protruding acicula. Leodamas platythoracicus sp. nov. can be recognized by its thorax, distinctly flattened in the posterior half and consisting of about 19 chaetigers, by its thoracic neuropodia, with many spines arranged in one or two rows and few, if any, slender capillaries, and by the shape of its abdominal neuropodia, which are long and subterminally notched and bear a distal process.

The Asian date mussel, Musculista senhousia (Mytilidae), is a good example of a species that has dispersed outwards from its native area through human-mediated transport, establishing sustainable populations in distant parts of the world. The date mussel, which is endemic in the Western Pacific region, appeared and became very abundant in the Sacca di Goro, a brackish lagoon in the Po River Delta (northern Adriatic Sea, Italy) in the early 1990s. Effects of M. senhousia on macrobenthic biodiversity were assessed over a ten year time period. At the study site, the increase in abundance and spread of M. senhousia resulted in an alteration of the pre-established macrobenthic community. Changes in benthic dynamics seemed apparent, through the inhibition of epifaunal, suspension-feeding taxa (Ficopomatus enigmaticus, Mytilaster minimus), and the enhancement of detritivores (Neanthes succinea, Streblospio shrubsolii, Microdeutopus gryllotalpa). It is hypothesized that the Asian date mussel was initially successful because it exploited a naturally disturbed, sparsely occupied environment, rather than interjecting itself among and displacing existing species. Musculista senhousia acted, at least initially, as a colonizer rather than an invader.

The new amphipod crustacean species Dikwa andresi from the Scotia Arc is described in detail. This is the first record of the family Dikwidae in the Southern Ocean. The white species was caught in water depth of 270–290 metres during the Antarctic autumn, living on the red hydrocoral (Hydrozoa) Errinopsis reticulum. It has a carinate pereon and pleon, no eyes and the head is telescoped into the first pereon segment. The first gnathopod is propodochelate, the second gnathopod is simple. The only known species of the family is Dikwa acrania from southern Africa. The new species mainly differs from D. acrania in having dorsal processes on all pereonites and the first coxa being twice as long as the second. An intraspecific variation of the shape of the telson was observed.

An evaluation was carried out on the distribution and abundance of the rock shrimp Rhynchocinetes typus in the inshore subtidal zone on the north-central coast of Chile. A number of different benthic community types occur in the region which have different degrees of spatial complexity provided by the primary substratum and by the biotic communities colonizing the substratum. Shrimp abundance was estimated in five different community types including shallow and deep ‘barren grounds’, low encrusting communities, erect suspension feeding associations, and kelp beds of Lessonia trabeculata. The abundance of shrimp was determined on three different types of primary substratum (stones, boulders, rock mass) within each community. Rhynchocinetes typus occurred in all the communities studied, showing the highest abundance on the deep barren grounds and lowest abundance on the shallow barren grounds. The shrimp was found to prefer the stony areas, as these offered the greatest degree of refuge. The abundance of predators was not significantly different among the different communities. However, a decline of abundance of predators was apparent over the deep barren grounds.

The spionid polychaete Dipolydora armata, a borer in calcareous substrata, is recorded for the first time from Belize, Brazil, Taiwan, and Vietnam. Specimens from these and other localities, as well as the type material of Polydora armata from Madeira Island and Polydora rogeri from the Mediterranean were examined and all the specimens were considered to be conspecific. Dipolydora armata is up to 8 mm long (usually 2–3 mm), with up to 45 segments (usually 25–35 segments), an incised prostomium, caruncle until the end of segment 2, up to 10 pairs of branchiae from segment 7, up to 20 awl-like modified spines per notopodium in up to 15 posterior segments, bilobed or cup-shaped pygidium, hooded hooks from segment 7 accompanied by capillaries throughout the body, major falcate spines of segment 5 with a large lateral tooth and an apical structure covered by fine bristles and appearing as a cowling or third tooth on the convex side of the main fang.  The life history of the species includes a period of asexual reproduction by architomy beginning soon after settlement, then sexual maturation and continuous breeding within an extended period with production of lecithotrophic larvae developing entirely inside egg capsules. Once mature, individuals probably reproduce only sexually and do not undergo additional architomic divisions.  Asexual reproduction results in high morphological variability of adult individuals, particularly in number, size, and arrangement of awl-like spines in notopodia. Polydora rogeri is placed into synonymy of D. armata. The original interpretation of the relationship between the polychaetes and the excavating sponge Cliona viridis as mutualistic symbiosis is discussed. Dipolydora armata is considered to be a widespread non-specialized borer perforating various calcareous substrata.

The proportion of berried (externally egg-bearing) females, fecundity, gonadosomatic index, and egg size of the blue swimmer crab Portunus pelagicus off southern Australia were examined by analysing data from samples of commercial catches using generalized linear models. Ovarian development was studied morphologically and histologically. Female blue swimmer crabs spawn from October to January and can spawn more than once per season. The fecundity of female blue swimmer crabs initially increased with carapace width, maximized at a carapace width of 134 mm, and decreased thereafter. Thus, fecundity increased 83.9% with an increase of carapace width from 105 to 125 mm, implying a single large female can produce as many eggs as two or more small females. The gonadosomatic index of female crabs from Spencer Gulf increased 2.4% from October 1998 to November 1998, increased an additional 15.9% by December 1998, and then decreased 62.3% to its minimum in January 1999. Gonadosomatic index also increased with 1/3 power of their body weight. Thus, the commonly used gonadosomatic index is overly simplistic for blue swimmer crabs. Unlike tropical or subtropical female blue swimmer crabs which often continually spawn, those off southern Australia spawn only in certain times of the year. The implications of this work lead to suggestions for three management measures for the commercial fishery: maintaining the prohibition of catching berried females, extending the seasonal closure from October to January, and maintaining the current legal minimum carapace width of 110 mm.

The first record of Musculista senhousia in the Taranto seas (eastern-central Mediterranean Sea) is reported. The species was mostly found on bottoms with pleustophytic algal felt where densities up to 3800 specimens per square metre were estimated. The sizes in the sampled population ranged from 5·16 to 30·59 mm. Two main modal components were detected around 11·67±0·67 mm and 18·00±2·38 mm.

The population structure of Mithraculus forceps sampled monthly on Anchieta Island from January 1999 to December 2000 was studied. A total of 68 individuals were collected by SCUBA diving. The population presented normal and unimodal distribution, and the total sex ratio was 1·4:1·0 in favour of males. Ovigerous females were captured during all seasons. The pattern observed for the M. forceps population in Anchieta Island indicated the strategy favoured by environmental characteristics of the island and by coexistence with other decapod crustaceans in the studied area.

The filter feeding bivalves Mulinia edulis and Mytilus chilensis, were exposed to a broad spectrum of concentrations and qualities of seston in order to compare the results of filtration rates measured volumetrically and gravimetrically, by both the traditional clearance method of Coughlan (1969) and the biodeposits method. Filtration rates, measured gravimetrically by both methods, tended to give similar results for both species, increasing with increase in seston and with decrease in seston organic content. With volumetric measurements, the filtration rates for both species also increased with the concentration of seston, however, in Mulinia edulis, the effect of the organic content of the food was less than that observed using gravimetric units, which is seen in the smaller slope of the regression equation (TFRv=−0·49). In the case of Mytilus chilensis there was no verifiable effect of the quality of the food on the filtration rate when expressed on a volume basis. The filtration rates of Mulinia and Mytilus measured by two methods and two units showed a similar behaviour with increase in the concentration of seston.

The diet of all chaetognath species found in a broad pelagic area of the eastern Mediterranean was investigated through gut content analysis. Eight chaetognath species were recovered from four depth intervals between 0 to 300 m in the Ionian, Cretan and Rhodes Seas and in the Cretan Passage. The mean food containing ratio (FCR) value for all chaetognaths combined was 0·048. Copepods comprised nearly 65% of the total food items consumed. The epipelagic species Sagitta enflata, Sagitta serratodentata atlantica, Sagitta bipunctata and Sagitta minima fed mainly in the 0 to 50 m surface layer, while the mesopelagic species Sagitta lyra, Sagitta decipiens, Sagitta hexaptera and Krohnitta subtilis fed in deeper layers. Sagitta s. atlantica showed the highest mean FCR in the integrated water column (0 to 300 m) of the whole sampling area. The estimated impact of chaetognath predation on copepod communities ranged from 0·3 to 7·8% of the copepod standing stock, and was higher in the Ionian Sea and the Cretan Passage than in the Cretan and Rhodes Seas. Sagitta s. atlantica, S. lyra, and S. decipiens had the most important predation impact among the eight chaetognath species found in the 0 to 50 m, 50 to 100 m and 100 to 300 m depth layers respectively.

Three species of Plakortis and one of Plakinastrella (Demospongiae: Homosclerophorida) collected mostly at oceanic islands off north-eastern Brazil (Atol das Rocas, Fernando de Noronha and São Pedro e São Paulo Archipelago) are described, three of which are new to science: Plakortis angulospiculatus, P. insularis sp. nov., P. microrhabdifera sp. nov, and Plakinastrella microspiculifera sp. nov. External morphological characters such as colour, oscules, and consistency are sufficient to discriminate all the four species in the field, except Plakortis angulospiculatus from P. microrhabdifera. Internal features such as skeletal arrangement, shape and size of diods, and presence of microrhabds and calthrops are also important taxonomic characters for western Atlantic Plakortis and Plakinastrella. We consider as valid only five species of Plakortis in the western Atlantic: the three species described here plus P. halichondrioides and P. zyggompha. All these species except P. zyggompha have been recorded from Brazil. Plakinastrella has now two species in the western Atlantic, P. onkodes and P. microspiculifera sp. nov. The generic distinction between Plakortis and Plakinastrella is tenuous, based only on the presence of spicule size-classes and of deformed vs normal calthrops, and both genera need detailed revision.

The parasitic copepod, Alimeda orientalis, is recorded from the gill of the sea hare, Dolabrifera brazieri (Gastropoda: Opisthobranchia: Anaspidea). Ten specimens of D. brazieri from a population on the coast of New South Wales, Australia were examined for the incidence of parasitism. Histological techniques and scanning electron microscopy were utilized to determine the feeding mode of A. orientalis and its effect on the host. Alimeda orientalis is a tissue feeder on the gill tissue, and damage caused by feeding and attachment is minimal.

Growth of seed mussel Mytilus galloprovincialis (Bivalvia: Mytilidae) from two origins (rocky shore and collector ropes) placed on raft culture was compared. Mussel seed were cultivated following the commercial culture phases commonly used in Galician Rías: (a) from seeding to thinning-out and (b) from thinning-out to harvest. Differences in growth rate were clearly related to the phase of the culture, being significant during the first phase from seeding to thinning out (January–November 1998). In the latter phase, weight values observed for collector rope mussels were significantly higher than those for rocky shore individuals (0·65 vs 0·45 g total dry weight, 0·11 vs 0·08 g tissue dry weight, 0·53 vs 0·37 g shell dry weight and 0·09 vs 0·07 g tissue organic weight per month, respectively; P<0·001). Neither shell length nor weight (soft tissue or shell) growth rate showed differences during the second phase of the culture from thinning out to harvest (November 1998–July 1999; P>0·05). Nevertheless, in terms of output, the higher number of individuals above 70 mm (77% vs 61%) and the heavier soft tissue (and total) weight (23–30%) for collector ropes mussels when compared to rocky shore ones at harvest, highlighted the importance of choosing the former stock. Condition index (CI) did not differ at the onset of the culture between both origins (P>0·05), but mussels from collector ropes showed significantly higher values than those from the rocky shore from May to November 1998 (P<0·001) before thinning-out was undertaken. No differences in CI were observed from thinning out to harvest between both types of mussels (P>0·05). Although both populations showed normal (unimodal) size distributions at the onset of the culture, mussels from rocky shore origin fitted better to bimodal profiles throughout the first phase of the culture. These bimodal distributions of rocky shore population did disappear during the second phase suggesting a more uniform size spectrum as a consequence of the thinning out process, which involves a selection of size.

The impact of experimental dredging was assessed on the venus clam Chamelea gallina from seabeds off the Lagoon of Venice. Commercial-sized clams were collected using high water pressure and mechanical sorting (HP), as in professional fishing, and low water pressure without sorting (LP). To highlight the effects of acute stress due to the different approaches in harvesting clams, various biological responses were evaluated at both organism and cell level. Filtration and respiration rates showed opposite behaviour, the former significantly decreasing, the latter increasing, when mechanical stress was higher. Consequently, lower values of scope for growth in HP clams were observed. The survival in air test exhibited significantly lower median survival time values (LT50) in more severely stressed animals. The haematocrit value and phagocytic index significantly decreased in HP samples, revealing a detrimental effect on mechanisms of immunological defence. Acid phosphatase and β-glucuronidase activity was also affected by increasing mechanical stress, even though an opposite trend was shown in the two investigated enzymes. Lastly, higher damage levels were detected in shells of HP clams.

Over the course of the moult cycle of Maja squinado, the spider crab changes in the hardness and colour of the carapace were assessed and used as methods to identify the intermoult stage in each individual. This intermoult staging was later verified by means of the microscopic observation of the maxilla. These staging techniques made it possible for the prompt identification of the principal intermoult stages—postmoult, intermoult and premoult. In 90% of the cases analysed, there was a correlation between the presence of an underlying carapace and a pink colour of the abdominal vein in crabs in advanced premoult stages.

The seasonality of the moult was studied based on the number of specimens in the postmoult stage. There were two main moulting periods—the first occurring in April, and the second, longer period was between July and November. A hypothetical growth model was established and growth rates were determined by length–frequency distribution analyses. Three groups of juveniles and one group of adults were identified. The adults were only found among the population between July and October. In both males and females, the moult increment rate was lower in terminal moults (mean=22%) than in juvenile or prepubertal moults (mean=27%).