Mean prevalence and intensity of infestations by epibionts were evaluated in Arenaeus cribrarius (Lamarck, 1818), based on monthly samplings (May/1991 to April/1993), in Ubatuba, Brazil. Bryozoans were quantified in terms of colony numbers and barnacles by the number of specimens. Prevalence of infestation was determined in 1,914 individuals of A. cribrarius and assessed with respect to sex, maturity stage and season. No significant interaction was detected between epibionts and biological host factors. Males showed a higher infestation rate by Chelonibia patula (Ranzani, 1818) when compared to mature non-ovigerous females, yet Octolasmis lowei Darwin, 1851 infestation was associated to adult crabs. The ovigerous females of A. cribrarius showed a higher prevalence of infestation than males and non-ovigerous females, with lower infestations being recorded during winter. A synchrony between the life cycle of the epibionts and their hosts was evident and promotes the continuity of the former in the area.

Swimming crabs are commonly found in the otter-trawl shrimp fishery by-catch, which operate intensively in the Coastal Plain of Leste Beach, where is located Shangri-lá Beach (25°37'30"S and 48°25'08"W), Paraná State. This work aimed to study the population structure of Callinectes ornatus Ordway, 1863, the most abundant swimming crab in this beach. Between March 2000 and April 2001, fortnightly visits were accomplished in Shangri-lá at the fish market, where all swimming crabs of one otter-trawl were collected. The following data from each individual of C. ornatus were obtained: sex, carapace width (excluding lateral spines), weight, and the gonadal maturation stage, based on its color and size. Juveniles and mature males were dominant, mean sexual proportion was 2.2:1 (males:females). Two recruitment periods were detected, but few ovigerous females were obtained. Size at sexual maturation was estimated at 55mm for males, and 48 mm for females. Both sexes presented positives allometric growths. The results indicate that an important portion of C. ornatus population is captured in the otter-trawl shrimp fishery in Shangri-lá Beach (Paraná). Such information is important for futures plans of by-catch management in that area.

Some individuals of the species Arenaeus cribrarius (Lamarck, 1818) bear a characteristic pink abdomen, which is notably different from the usual white coloration. The incidence of this chromatic alteration was determined for a single population and its relation with other individual variables were examined. The individuals were monthly collected from May, 1991 to April, 1993, in Ubatuba, São Paulo, with the aid of a shrimp fishery boat provided with double-rig trawling nets. All specimens were sexed, measured (CW = carapace width), distributed in 10-mm size classes and classified according to growth phase (juvenile and adult), molting condition and development stage of gonads. The occurrence of pink-colored morphs was also recorded. From a total of 2,096 collected individuals, only 60 females (nine of those ovigerous) presented a pink-colored abdomen, which represents 2.9% of the whole sample and 5.2% of the females. Almost all of them were intermolt individuals (96.6%) and 63.3% showed mature gonads. According to published data, size at the onset of functional maturity in A. cribrarius females is around 60 mm CW, from which the incidence of pink morphs and ovigerous crabs were recorded. The obtained results suggest that such a chromatic alteration is associated to sexual maturity in these females. This characteristic may enhance the attraction potential for mating, shortly after the puberty molt.

The niche breadth of the Portunidae and their overlap on the subtidal sediments of Fortaleza bay, Ubatuba (São Paulo) was analyzed. Samples were made monthly from November/1988 to October/1989, inseven areas of the bay using a shrimp fishery boat equipped with two otter-trawls. Each area was characterized based on environmental factors such as depth, temperature, salinity, dissolved oxygen, organic matter and granulometric composition of the sediment. The number of individuais of each species was registered to each area (resource). Levins's standardized measure (BA) and niche percentage were calculated. Five species of swimming crabs were recorded in this study: Callinectes ornatus Ordway, 1863, Arenaeus cribrarius (Lamarck, 1818), Portunus spinimanus Latreille, 1819, Callinectes danae Smith, 1869 and Portunus spinicarpus (Stimpson, 1871). The widest ecological niche occurred to C. ornatus, present in all sampled areas (generalist species). Such fact can be related to high sediment tolerance when it is compared to P. spinimanus (especialist species) which was limited to the areas with coarse granulometric fractions. Highest niche overlap was verified between C. danae and A. cribrarius may be due to greater salinity tolerance of these species. The low occurrence of P. spinicarpus and its reduced niche size in Fortaleza Bay are due to association of this species to cold water currents (ACAS) more evidente in smaler depths during summer months. One future evaluation of the portunid diet can be useful to complement informations about this important aspect of the marine ecology.