Neustonic distribution of decapod planktonic stages and competence of brachyuran megalopae in coastal waters

Settlement rate may not reflect larval supply to coastal waters in different marine invertebrates and demersal fishes. The importance of near-shore oceanography and behaviour of late larval stages may be underestimated. The present study conducted neustonic sampling over station grids and along full-length transects at two embayments in south-eastern Brazil to (1) compare diurnal and nocturnal occurrence of most frequent decapod stages to assess their vertical movements, (2) describe the formation of larval patches and (3) measure competence of crab megalopae according to their distance to recruitment grounds. Several shrimp species apparently undergo a diel vertical migration, swimming crab megalopae showed no vertical movements and megalopae of the intertidal crab Pachygrapsus transversus revealed a reversed vertical migration. During the day, crab megalopae aggregated in convergence zones just below surface slicks. These larvae consisted of advanced, pre-moult stages, at both mid-bay and near-shore patches. Competence, measured as the time to metamorphosis in captivity, was similar between larval patches within each taxon. Yet, subtidal portunids moulted faster to juveniles than intertidal grapsids, possibly because they were closer to settlement grounds. Megalopae of Pachygrapsus from benthic collectors moulted faster than those from bay areas. These results suggest that alternative vertical migration patterns of late megalopae favour onshore transport, and actual competence takes place very close to suitable substrates, where larvae may remain for days before settlement. Lack of correlation between larval supply and settlement for Pachygrapsus suggests that biological processes, besides onshore transport, may play an important role in determining settlement success of coastal crabs.

Juvenile development of the crab Bathyrhombila sp (Crustacea, Decapoda, Pseudorhombilidae) from megalopae obtained in the neuston

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Juvenile development of Callinectes ornatus Ordway, 1863 (Crustacea : Decapoda : Portunidae), from megalopae obtained in the neuston

The juvenile development of Callinectes ornatus was studied from megalopae collected in the neuston off Ubatuba, São Paulo State, Brazil. The animals were raised in the laboratory under constant temperature (25 +/- 1 degrees C), filtered sea water (35 parts per thousand) from the sampling location, and the natural photoperiod. Eleven stages of the juvenile phase were obtained. The main features of the first juvenile stage diagnostic of the species are: the number of segments in the antenna; number of setae on the exopod, endopod, basal endite and coxal endite of the maxilla, on the exopod, endopod, basal endite, coxal endite and epipod of the 1(st) maxilliped, and on the exopod, endopod and epipod of the 2(nd) maxilliped. Sexual dimorphism becomes apparent from the fourth juvenile stage onwards.

Survival of Ucides cordatus (Decapoda: Ocypodidae) megalopae during transport under different conditions of density and duration

Target areas for Ucides cordatus (Linnaeus, 1763) restocking programs are often located far from the laboratory where larval rearing is developed. During translocation, the larvae are submitted to highly stressful conditions due to handling, packing, and transport activities. The aim of the present study was to assess the mortality rates of U. cordatus megalopae caused by different transportation procedures. Megalopae at loading densities of 50, 150, and 300 ind.L-1 were packed in double polyethylene 12 x 25 cm plastic bags with 200 ml of marine water at salinity 30. The bags were filled with oxygen at a proportion of 1:2 parts of water and sealed tightly. The trepidations during transport were simulated by the use of a shaker device (800 vibrations/minute) over periods of three and six hours inside a dark container. The survivorship rates of larvae after simulation were compared to those obtained in control groups, which consisted of plastic vials with megalopae at a loading density of 50 ind.L-1 maintained at rest. Immediately after the two transport simulations, there was no significant difference in survivorship between the treatments and the control. However, 24 hours after simulation some of the tested densities resulted in significantly lower survivorships. The results demonstrated that U. cordatus megalopae can tolerate six hours of shaking during transportation, at high densities with minimal mortality.

Horizontal distribution of megalopae of Brachyura (Crustacea, Decapoda) in a South American tropical estuary

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Vertical migration during tidal transport of megalopae of Necora puber in coastal shallow waters during daytime

For meroplanktonic larvae that must settle in coastal areas, their successful return to the shore is determined largely by physical transport processes; however, many organisms perform vertical movements to aid successful recruitment. In this study, daytime tidal vertical migration of megalopae of the velvet swimming crab Necora puber was investigated across two different exposures in the shallow waters of Plymouth Sound. Crabs were collected using a plankton net at the surface and near the bottom during flood and ebb tides. Distribution of the pelagic postlarvae was patchy and the abundance varied spatially in tens and thousands of metres. In temporal scales, the annual pattern was dominated by low occurrence of megalopae, punctuated by episodic peaks of high abundance. Most megalopae were collected at the surface irrespective of the tidal phase. The effect of wave exposure on the vertical migration of megalopae was not clear, although there was a general higher abundance of megalopae on exposed shores. Daytime abundance in the water column appears to be regulated by the tidal cycle, as megalopae were more abundant during flood than ebb tides. Although the megalopae do not appear to make large vertical migrations, this behaviour should produce a net shoreward transport. © 2005 Elsevier Ltd. All rights reserved.

Longitudinal distribution and lateral pattern of megalopal settlement and juvenile recruitment of Carcinus maenas (L.) (Brachyura, Portunidae) in the Mira River Estuary, Portugal

Settlement is a critical process in the life history of crabs, and thus affecting the abundance, distribution and structure of estuarine communities. The spatial pattern of settlement of megalopae of the shore crab Carcinus maenas along a longitudinal estuarine gradient (Mira River Estuary, Portugal) was examined, as well as its effects on the juvenile population. To measure megalopal settlement, four replicate collectors were deployed in six equally spaced stations along the estuarine axis. Juveniles were collected on the same locations with a quadrat randomly deployed on the substrate. To assess fine-scale megalopal settlement within a curved region of the estuary, replicate collectors were deployed on both margins along Moinho da Asneira curve. Megalopae settled differently along the six longitudinal points, with a tendency to attenuate their settlement upstream. Within the curved region, megalopae preferentially settled on the left margin collectors, probably due to the weaker velocity speeds felt on this margin. Concerning the overall juvenile density, there were significant differences among the stations distributed along the estuary, but they did no reflect a longitudinal dispersion attenuation pattern. Size-frequency distribution of the juvenile population showed that the average size is higher on the left margin. Recruits (carapace length between 1.0 mm and 3.4 mm) were more abundant on the upstream stations. Density of early juveniles (3.4 mm-6.5 mm) and juveniles (6.5 mm-10 mm) was more stable throughout the estuary axis than that of recruits. This distribution pattern may result from tidal excursion processes or mechanisms to avoid biotic interactions, such as predation and competition. (c) 2006 Elsevier Ltd. All rights reserved.

Aspectos biológicos do peixe-olhudo-dentinho, Synagrops bellus (Actinopterygii: Acropomatidae), da plataforma externa e talude superior do estado de São Paulo, Brasil.

Biological aspects of the blackmouth bass Synagrops bellus from the outer shelf and upper slope along the coast of São Paulo, southeastern Brazil, are presented. The species represented about 71.6% and 9.7% in number of the total catch performed by balloom trawl in the isobaths of 300m and 500m respectively. Body sizes of 266 individuals ranged between 130 and 265mm total length, with sex ratio of 55.9% males, and 44.1% females, where most individuals were in maturation stage. Twenty two food items were found, pointing out Myctophidae fishes, Penaeidea and Caridea shrimps, Brachyuran megalopae, Enoploteuthidae and Cranchiidae cephalopods, pteropods and tunicates. The intestinal coefficient increases as the body size increase, and the number of gill rakers ranged between 16 and 17. Length-weight relationship was WT = 6.0 x 10-6 x TL3.12, r2 = 0.9495. Synagrops bellus is an important link between zooplankton and micronekton, and demersal and pelagic predators in the outer shelf and upper slope in southwestern Brazilian coast.

Early juvenile development of Armases rubripes (Rathbun 1897) (Crustacea, Brachyura, Sesarmidae) and comments on the morphology of the megalopa and first crab

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The megalopa and juvenile development of Pachygrapsus transversus (Gibbes, 1850) (Decapoda, Brahyura) compared with other grapsid crabs

Megalopae were reared in the laboratory to the 7(th) crab stage. The megalopa and 1(st) crab stage are described and juvenile development was studied with emphasis on pleopodal differentiation. The megalopal phase, is easily identified, and shares with those of other Grapsinae and Plagusiinae big size, the presence of many natatory setae, and a series of conspicuous teeth on the inner margin of the dactyli from the 2(nd) to 4(th) walking leg. These features are regarded as adaptive for settlement in a wave-swept environment, such as the rocky marine intertidal where most of those species live. Fast development of juvenile pleopods is another characteristic of these subfamilies. In Pachygrapsus transversus, the sexes can be distinguished from the 2(nd) crab stage. Gonopod differentiation in males and the basic segmentation of all four pleopod pairs in females are already concluded at the 5(th) instar. A review of the available information indicated that settlement of large megalopae and fast juvenile development, preceding a precocious sexual maturity, are trends in Grapsinae and Plagusiinae. on the other hand, the Sesarminae pass through a more extensive juvenile instar sequence and presumably a delayed maturity.

The megalopa and early juvenile development of Hepatus pudibundus (Crustacea: Brachyura: Aethroidea) reared from neuston samples

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Larval cannibalism rates in the mangrove crab Ucides cordatus (Decapoda : Ocypodidae) under laboratory conditions

Predation of zoeas by megalopae of Ucides cordatus is frequently observed in the laboratory during larval rearing, a phenomenon that could considerably reduce the output of larviculture. Experiments were carried out in the present study to assess how the survivorship of larvae at the end of the larviculture is influenced by cannibalism by megalopae on the larvae of earlier stages, as well as on other megalopae. In addition, tests were performed to assess whether the adoption of different feeding protocols can decrease cannibalism rates. Experiments were carried out in plastic vials containing ocean water (salinity 25 g L-1) under controlled environmental conditions (26 degrees C and 16:8 h LD photoperiod). An ensemble analysis of all the developmental stages indicated that zoeal mortality rates were significantly higher in the presence of megalopae, a result that is consistent with cannibalism by megalopae. However, separate analysis for each developmental stage indicated that only zoea IV, V and VI show reduced survivorship. No cannibalism was detected among megalopae. Food supplementation using Artemia sp. at a density of 6 nauplii mL(-1) proved to be successful in reducing cannibalism rates, whereas supplementation at a lower density (0.3 nauplii mL(-1)) failed to show such an effect. The implications of these results for the larviculture of U. cordatus are discussed.

FIRST ZOEAL STAGE and MEGALOPA of UCA (UCA) MARACOANI (DECAPODA: BRACHYURA), WITH COMMENTS on THE LARVAL MORPHOLOGY of SOUTH-AMERICAN SPECIES of OCYPODIDAE

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Desenvolvimento larval de Eriphia gonagra (Fabricius, 1781) (Decapoda, Xanthidae), em laboratório

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The megalopa and early juvenile stages of Calappa tortugae Rathbun, 1933 (Crustacea, Brachyura) reared in the laboratory from South Carolina neuston samples

Neuston samples collected from the Charleston Bump region off the coast of South Carolina, U.S.A., during the summers of 2002 and 2003 consistently included a decapod species of undetermined identity with a large brachyuran megalopa. Despite their resemblance to some calappids, it was impossible to make a definitive identification based solely on general morphology. Therefore, additional neuston tows were taken on the continental shelf near Charleston, during the summer of 2004 to obtain these living megalopae. These were raised successfully through five juvenile stages at the Southeastern Regional Taxonomic Center (SERTC) laboratory. The morphology of the juveniles provided evidence that they are megalopae of Calappa tortugae Rathbun, 1933. Comparisons with megalopae of Hepatus epheliticus (Linnaeus, 1763), H. pudibundus (Herbst, 1785), Calappa flammea (Herbst, 1794) and Cryptosoma balguerii (Desbonne, 1867) are presented here. This is the first complete description of the megalopa morphology of a member of the genus Calappa Weber, 1795 from the Western Atlantic, and it is helpful for taxonomic, systematic and ecological purposes.