Robson Ventura

Duration of the pre-settlement period of the mangrove crab Ucides cordatus (Decapoda: Ocypodidae) under laboratory conditions

O estagio de desenvolvimento em que se encontram as formas jovens de caranguejo produzidas em laboratorio, no momento da sua liberacao para o ambiente, e um fator chave para o sucesso dos trabalhos de repovoamento. O presente trabalho teve como objetivo determinar a idade mais adequada das formas jovens de U. cordatus, produzidas em laboratorio, para sua liberacao no ambiente natural. Especificamente, o momento em que as megalopas procuram o sedimento de mangue para escavar tocas foi determinado, assim como o tempo que demoram ate realizarem a metamorfose para o primeiro estagio juvenil. O experimento indicou que as megalopas de U. cordatus produzidas em laboratorio levam de 3 a 10 dias (mediana = 6) apos a metamorfose ate escavarem tocas no sedimento. O tempo medio que as megalopas levaram ate realizar a metamorfose para o primeiro estagio juvenil foi de 12,6 dias (desvio padrao = 2,33).

Diferentes rotas de desenvolvimento larval do caranguejo Ucides cordatus (Decapoda, Ocypodidae) e sua relação com altas taxas de mortalidade no fim de larviculturas massivas

One of the most limiting factors affecting the larval rearing of Ucides cordatus in the laboratory is a period of high mortality, which usually occurs late in the course of the larviculture during the metamorphosis from the zoeal to the megalopal phase. The objective of the present research was to analyze the post-embryonic development of U. cordatus on an individual basis and, in particular, to search for patterns linking disturbances in the molting process to the high larval death rates observed in massive larvicultures. A total of 50 larvae were individually reared from hatching to metamorphosis into the megalopal phase under controlled conditions, fed a combination of microalgae and rotifers. The survivorship rate was 70% until zoea V. The 35 surviving zoea V larvae followed two different pathways. Eleven underwent metamorphosis directly to megalopa, eighteen molted to zoea VI and six died as zoea V. In the last molting event, only two zoea VI larvae reached the megalopal stage, while the remaining sixteen died. In further observation under microscope, 13 of the dead zoea VI showed characteristics of the pre-molt stage and pereiopods disproportionably large in relation to the carapace. The observed pattern resembles the Molt Death Syndrome (MDS) described for other decapod species, in which larvae die in the late pre-molt phase of the molting cycle. We suggest that U. cordatus larvae develop disturbances in the molting process similar to the MDS described for other species and that these disturbances are related to a more complex pathway involving the emergence of larval stage zoea VI.

Fish predation on brachyuran larvae and juveniles in the Pinheiros river, Guaratuba Bay, Paraná, Brazil

Fish predation is thought to exert an important influence on the demographical dynamics of larvae and juveniles of estuarine brachyuran crabs but few studies have investigated this phenomenon in nature. In this study, fishes were captured during full moons (in January and February 2005), when many brachyuran species are known to release their larvae. Samples were carried out in the Pinheiros river, Guaratuba Bay, Parana, Brazil. The stomach contents of collected fishes were surveyed to determine the species that are most likely to prey on brachyuran immature forms in this location. Two techniques were used to capture fishes: manual samplings, using a 5-mm mesh size net (1.8m depth), and bottom trawling with a 20-mm mesh size net. The collected specimens were fixed using 10% formaldehyde and preserved in 70% ethanol. A total of 2941 fishes of 43 different species were collected and the stomach contents of 962 individuals were analyzed in laboratory. Food items were identified and quantified. The fish species captured using manual nets that showed the highest number of preyed zoeae per stomach was the clupeid Platanichthys platana (Regan, 1917). Sphoeroides testudineus (Linnaeus, 1758) and Centropomus parallelus Poey, 1860 showed the highest levels of predation on megalopae. Of the fish species captured using trawl nets, Genidens genidens (Cuvier, 1829) showed the highest average number of zoeae per analyzed stomach and Bairdiella ronchus (Cuvier, 1830) was the most important predator on brachyuran megalopae and on young juveniles. The obtained data indicate that brachyuran crab restocking efforts performed in the Guaratuba Bay should include strategies to avoid or, at least, reduce the access of fishes to the released early juvenile stages, given the potential substantial losses caused by fish predation. Considering that, in general, predation potential was 8.5 times lower in juveniles than in megalopae, releasing immature forms produced in laboratory in the juvenile phase or releasing megalopae into tethered areas and maintaining than under this condition until they reach the juvenile phase may be tested as a method to reduce losses given to fish predation.

Intraspecific interactions in the mangrove crab Ucides cordatus (Decapoda: Ocypodidae) during the metamorphosis and post-metamorphosis periods under laboratory conditions

Current efforts for restocking natural populations of the mangrove crab Ucides cordatus (Linnaeus, 1763) in Brazil have focused on developing a methodology for stimulating the metamorphosis of U. cordatus larvae at a large scale. The aim of the present study was to compare the mortality rates both in individual and mass conditions, during the induction of metamorphosis of megalopa to juvenile in U. cordatus, without the use of mangrove sediment as substrate. Furthermore, the importance of intraspecific antagonistic behavior on survivorship rates during early post-metamorphosis period was investigated. Metamorphosis was induced by the use of water conditioned with conspecific adults (30 indiv. 100 L-1 for 24 hours). In the first assay, megalopae were stimulated into metamorphosis in experimental vials, both under individual and mass rearing conditions. The second assay assessed the interactions between megalopae and first instar juveniles, which have metamorphosed for more than 24 hours. In the third assay, the existence of cannibalistic behavior among first instar juveniles under different experimental densities was investigated. Significant differences between survivorship rates of individuals that metamorphosed under individual and mass rearing conditions were detected. However no cannibalistic behavior between juveniles and megalopae was observed in the second assay. Juveniles reared at a density of 200 indiv.m-2 showed survivorship rates similar to those obtained under individual conditions. Yet 500 juveniles.m-2 treatments showed significantly lower survivorship rates. Intraspecific interactions appear to be an important problem in U. cordatus specifically during the metamorphosis, but not during larval and post-larval rearing.

Restocking Ucides cordatus (Decapoda: Ocypodidae): interespecific associations as a limiting factor to the survival of released recruits

Simulacoes em laboratorio foram efetuadas visando investigar se apos liberacao na natureza a sobrevivencia de recrutas de Ucides cordatus produzidos em laboratorio e afetada por outras especies de caranguejos. Adicionalmente, foi verificado se com a liberacao de juvenis no estagio 1, ao inves de megalopas, haveria reducao da mortalidade causada por predacao interespecifica. Para tanto foi realizada estimativa previa da estrutura da comunidade de caranguejos presente na area-alvo de um programa de repovoamento em desenvolvimento na regiao de Santo Amaro, Baia de Todos os Santos, Brazil, cujos resultados mostraram grande dominância de caranguejos violinista (Uca spp.). Com base nessa informacao, foram realizados experimentos para verificar as relacoes ecologicas entre megalopas e juvenis 1 de Ucides cordatus e as diferentes classes de tamanho das outras especies de Uca, em presenca de sedimento do mangue, simulando condicoes naturais, e na ausencia de refugio. Observou-se que os caranguejos violinista competem predando tanto juvenis quanto megalopas de Ucides cordatus. Alem disso, foi visto que esse comportamento de predacao e exercido apenas por individuos com largura de carapaca maior que 0,5 cm. Os resultados do teste de simulacao das condicoes do ambiente natural evidenciaram que o mesmo padrao de predacao foi observado mesmo quando o sedimento foi oferecido como refugio, sendo as taxas de sobrevivencia significativamente menores na presenca de especies de Uca.

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.

Influência do cultivo de camarões marinhos em tanque-rede sobre a qualidade da água e a estrutura da comunidade zooplanctônica na Baía de Guaratuba, Paraná

Grupo Integrado de Aquicultura e Estudos Ambientais, Universidade Federal do Parana, Curitiba, PR, Brasil