Abstract
<p>The red mangrove crab, <em>Goniopsis cruentata,</em> influences the recruitment and composition of plant species in the mangrove ecosystem and it is an important fishery resource. Nevertheless, no current management and conservation plans are available for this species for the Brazilian coast. This investigation evaluated the population structure and reproductive biology in populations of <em>G. cruentata</em> under contrasting fishery pressures. The sampling program was carried out in two mangroves, Vaza-Barris and Sergipe River, from January through December 2011. Crabs from both mangroves were randomly collected by a professional fisherman during daytime low tide periods, using a fishing rod baited with pieces of a locally abundant gastropod, <em>Pugilina morio</em>, during 20min/area (catch per unit effort). Monthly measurements of air, sediment surface layer and water temperatures were obtained with a digital thermometer and salinity with an optical refractometer. Both crab populations were compared concerning their abundance, body size, sex ratio, size at onset of sexual maturity and fecundity (FI). Abiotic factors (air, water and mud temperature; and salinity) showed no significant differences between sampling localities. A total of 4 370 crabs were sampled, 2 829 from the Sergipe River and 1 541 from the Vaza-Barris River. The abundance and body size of crabs were compared between mangroves, and statistically significant differences were found. The sex ratio for both populations differed from the expected 1:1 ratio, and a significant deviation in favor of juvenile males was obtained, while adults showed a bias toward females. The estimated size at onset of sexual maturity for both sexes was similar in both populations. However, the populations differed significantly in the number and volume of eggs: a higher FI was obtained in females from the Sergipe River, while a higher egg volume was observed in females from the Vaza-Barris River mangrove. These results indicated a tendency to decrease the body size, the abundance of crabs and the reproductive potential of the species, with higher fishing intensities, reinforcing the need to develop a management plan as well as to establish conservation units for <em>G. cruentata</em> in the Northeastern Brazilian coast. Habitat loss in conjunction with long-term overfishing can have irreversible consequences, which can impact not only the populations of commercially exploited crabs, but the dynamics of virtually the entire mangrove ecosystem.</p>
Highlights
Crabs of the families Ocypodidae, Ucididae, Sesarmidae and Grapsidae are among the most abundant and ecologically significant animals found in mangrove ecosystems, where they play a key role in food webs and energy flow (Macintosh, 1988; Schubart, Cuesta, & Felder, 2002; Kristensen, 2008)
Goniopsis cruentata is one of the most abundant grapsid crabs of mangrove ecosystems in the Brazilian South Atlantic, and the trophic role of this crab in the ecosystem is wider than that observed for sesarmid and ocypodid mangrove crabs (Lima-Gomes, Cobo, & Fransozo, 2011)
The abundance of crabs was compared between mangroves, and statistically significant differences were found in relation to the Abiotic Parameters Air Temperature Water temperature Mud temperature Salinity
Summary
Crabs of the families Ocypodidae, Ucididae, Sesarmidae and Grapsidae are among the most abundant and ecologically significant animals found in mangrove ecosystems, where they play a key role in food webs and energy flow (Macintosh, 1988; Schubart, Cuesta, & Felder, 2002; Kristensen, 2008). Some researchers have reported an apparent decline in stocks of G. cruentata under different impacts, such as, cutting trees and discharge of solid waste (Menezes, Araújo, & Calado, 2012), as well as decreased body size of these crabs (Maciel, & Alves, 2009) This is a matter for concern, as no management plan has yet been developed to ensure the conservation of natural stocks of this species in Brazil. Recent fishery statistics for the Sergipe coast showed different results, estimating the harvest for the year 2010 alone at 115 tons (Souza, Dantas-Junior, Silva, Félix, & Santos, 2012) This estimate exceeds the average annual production for all of Northeastern Brazil, estimated by IBAMA at about 71.87±38.25tons/year. This is alarming because underestimation of fishing of G. cruentata on the Northeast coast of Brazil may be hiding the actual situation of overfishing of stocks of this species
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