Abstract The exploited mangrove crab Ucides cordatus, an important ecosystem engineer in South American mangroves, has a biphasic lifecycle with pelagic larvae developing offshore. Megalopae return to the mangrove forest to settle, i.e., metamorphose into benthic juveniles but its environmental drivers remain poorly understood. We postulate that conspecific crabs facilitate recruitment. In the field, we investigated whether the number of recruits is higher near conspecific burrows than in areas without conspecific bioturbation. Recruit sampling was conducted monthly from April 2008 to May 2009 along an environmental gradient. First, U. cordatus recruits of that year emerged from March to July. Intraspecific facilitation was indicated by significantly higher recruit numbers in bioturbated than in non-bioturbated substrates. Recruits were most abundant in zones with intermediate conditions of inundation, leaf litter standing stock, sediment consistency, luminosity, temperature, salinity, and pH. Avoidance of more inundated zones likely reduces predation by fishes and of less inundated zones helps individuals escape more stressful, drier environmental conditions. The observed habitat-specific recruitment pattern must be considered when designing field assessments of the population structure of U. cordatus (which should include sampling recruits) and enhancing stocks by releasing laboratory-cultivated larvae and first juveniles into the wild.

Megalopas de muitas espécies de caranguejos decápodes aceleram seu período de desenvolvimento até a metamorfose (TOM) quando são expostas a estímulos naturais físicos e/ou químicos característicos do habitat parental. No presente estudo, a influência de estímulos naturais sobre as taxas de muda e sobre o PDM foi investigada nas megalopas do caranguejo violinista Uca vocator. Os efeitos da (i) lama de diferentes habitats (incluindo habitats de um manguezal bem preservado e de um degradado e poluído) e (ii) 'odores' dos adultos conspecíficos (água do mar acondicionada com caranguejos) sobre a indução da metamorfose foram comparados com (iii) água do mar pura e filtrada (controle). 95 a 100% das megalopas realizaram a metamorfose com sucesso para o primeiro estágio de caranguejo juvenil em todos os tratamentos, incluindo o controle. No entanto, o PDM diferiu significativamente entre os tratamentos. Os estímulos encurtaram significativamente o desenvolvimento, enquanto que a muda foi retardada na ausência deles. O fato de que as megalopas responderam aos estímulos indutores da metamorfose oriundos de ambos os habitats bentônicos dos adultos e de habitats onde eles são ausentes, demonstra que o assentamento nesta espécie pode ocorrer em uma grande variedade de habitats dentro do ecossistema de manguezal, incluindo áreas impactadas.

Megalopae of many decapod crab species accelerate their development time to metamorphosis (TTM) when exposed to natural physical and/or chemical cues characteristic of the parental habitat. In the present study, the influence of natural settlement cues on the moulting rates and development TTM in megalopae of the fiddler crab Uca vocator was investigated. The effects of mud from different habitats (including well-preserved and degraded-polluted mangrove habitats) and conspecific adult 'odours' (seawater conditioned with crabs) on the induction of metamorphosis were compared with filtered pure seawater (control). 95 to 100% of the megalopae successfully metamorphosed to first juvenile crab stage in all treatments, including the control. However, the development TTM differed significantly among treatments. Settlement cues significantly shortened development, while moulting was delayed in their absence. The fact that megalopae responded to metamorphosis-stimulating cues originating from both adult and non-adult benthic habitats demonstrates that settlement in this species may occur in a wider range of habitats within the mangrove ecosystem, including impacted areas.

Recruits of the mangrove crab Ucides cordatus (Linnaeus, 1763), rarely encountered in the field were found co-inhabiting burrows of larger male and female conspecifics in the mangrove forest. They were located in the sediment of the inner walls and burrow plugs. Average carapace width (CW) of the hosting and co-inhabiting crabs was 3.8 ± 0.20 and 0.9 ± 0.03, respectively. As shown by the size-frequency distribution, while most recruits leave the conspecific burrows after reaching 1.0 cm CW, some stay until they reach a size of 2.5 cm CW. The results of this study contribute to a better understanding of recruitment patterns in this ecologically and economically important mangrove crab species. Follow-up studies are however needed to fully determine the role of conspecific burrows for juvenile habitat choice and survivorship in U. cordatus.

O presente trabalho estudou o efeito da salinidade na sobrevivência e na duração do desenvolvimento larval do caranguejo-uçá, Ucides cordatus (do estuário do Rio Caeté, Norte do Brasil), até a fase de megalopa em sete tratamentos de salinidade (0, 5, 10, 15, 20, 25 e 30). A salinidade afetou significativamente a sobrevivência das larvas zoea, no entanto não afetou a duração do desenvolvimento larval (20,77 ± 1,56 dias). Nas salinidades 0, 5 e 10 houve total mortalidade das larvas zoea. Somente a partir da salinidade 15 observou-se um desenvolvimento completo até a fase de megalopa. A taxa de sobrevivência foi maior em salinidade 30 (72%) e menor em 15 (16%). A reduzida taxa de sobrevivência das larvas zoea de U. cordatus, em salinidades baixas, indica a necessidade de dispersão larval do estuário para as águas costeiras onde as condições de salinidade para o desenvolvimento larval são mais favoráveis. Caso contrário se não houvesse a dispersão, a reduzida salinidade das águas estuarinas no período chuvoso, causaria uma elevada mortalidade, afetando desta forma o recrutamento, a manutenção e o crescimento da população de U. cordatus nos manguezais.

The present work studied the effect of salinity on the survival and duration of larval development of the mangrove crab, Ucides cordatus (from the Caeté River estuary, North of Brazil) until the megalopal phase in seven salinity treatments (0, 5, 10, 15, 20, 25 e 30). Salinity significantly affected the survival of the zoea larvae, however it did not affect the duration of the larval development (20.77 ± 1.56 days). In salinity 0, 5 and 10 all zoea larvae died. Only from off salinity 15, complete development until the megalopal phase occurred. The survival rate was highest in salinity 30 (72%) and lowest in 15 (16%). The reduced survival rate of the U. cordatus zoea larvae, in low salinities, indicates the necessity of larval dispersion from the estuary to coastal waters, where salinity conditions for larval development are more favorable. Otherwise, if there was no dispersion, the reduced salinity of estuarine waters in the rainy season would cause a high mortality thereby affecting the recruitment, maintenance and growth of the U. cordatus population in the mangroves.