Population dynamic of Sesarma rectum (Crustacea, Brachyura, Sesarmidae) from a muddy flat under human impact, Paraty, Rio de Janeiro, Brazil

Abstract

ABSTRACT. A population of Sesarma rectum Randall, 1840 under the influence of human impact was studied. Monthly sampling (CPUE, two people during 30 min) took place from August/2001 to July/2002 at an impacted muddy flat in Paraty city, State of Rio de Janeiro (23 º 13'S, 44 º 42'W). At the laboratory, specimens were classified by sex and measured with a vernier caliper (0.01 mm). The size at the beginning of the sexual maturity was obtained by means of different techniques: in the case of males it was used the allometric procedure and the macroscopic analysis of gonads wile for females, the size of the smallest ovigerous female was also considered. The population structure was evaluated by means the analysis of the variations in the modes of the size frequency distribution. The fecundity was assessed using sub samples of the egg mass. For males, the macroscopic analyses of gonads revealed larger values of carapace width than those obtained with morphometric analysis. Males larger than 18.5 mm of carapace width can be considered as mature. For females, such size was 17.4 mm CW. Despite of the human impact in the habitat, the population presented to be stable, as indicated by a single mode on the size frequency distribution. The second mode that appeared in some months is probably related to the entrance of juveniles in the population. The sex ratio of this population is closely approximating to 1:1 until crabs reach a carapace width of about 28 mm; after that, males outnumbered females. Comparing the fecundity of the present population with a previous study from Ubatuba, it can be verified a difference in the number of eggs. The fecundity of Paraty's population is significantly lower than the Ubatuba's population. This is probably related to the scarcity of food resource in Paraty, once no vascular plant can be found in that place. The continuity of reproductive processes and the juvenile recruitment suggest this species is able to live in the area with human impact. The ability to obtaining nutrients from different source of food is probably a feature that allows S. rectum to occupy such impacted ecosystem. KEYWORDS.Sexual maturity, allometric growth, population structure, fecundity. . O tamanho do início da maturidade sexual foi obtido por meio de diferentes técnicas: no caso dos machos, utilizaram-se técnicas alométrica e a análise macroscópica das gônadas, enquanto para as fêmeas, o tamanho da menor fêmea ovígera também foi considerado. A estrutura da população foi avaliada pela análise da variação das modas da distribuição de freqüência por classes de tamanho. A fecundidade foi obtida por meio de subamostragens das massas de ovos. Para os machos, a análise macroscópica das gônadas revelou valores da largura da carapaça maiores que os obtidos com as análises morfométricas. Machos maiores que 18,5 mm de largura da carapaça foram considerados maduros. Para as fêmeas, o tamanho da maturidade foi 17,4 mm de LC. Apesar do impacto humano sobre o ecossistema, a população apresenta-se estável, o que é indicado pela ...

Population dynamics ofSesarma rectum(Crustacea: Brachyura: Grapsidae) in the Ariquindá River mangrove, north-east of Brazil

“…The middle phase, here named 'transitional', is evident from 8.35 to 17.75 mm CW, where we can find either immature or mature crabs. This abdomen pattern growth was observed for other populations of S. rectum (Leme, 2005;Silva et al, 2007), and other species of mangrove crabs, such as Uca thayeri Rathbun, 1900 and Uca maracoani Latreille, 1802-1803 . According to Negreiros-Fransozo et al (2003), the first group of adult females could be represented by primiparous females, but further studies are necessary to confirm such a hypothesis.…”

“…Most of the studies on S. rectum have treated population and reproductive aspects, but all have been carried out on populations in south-eastern Brazil (Mantelatto & Fransozo, 1999;Leme, 2002Leme, , 2004Leme, , 2005Silva & Chacur, 2002;Silva et al, 2007). In view of the ecological importance of S. rectum in the mangrove ecosystem and also because of the lack of studies on this crab in north-eastern Brazil, we designed this study to provide information on its population ecology in mangroves of the Ariquindá River mangrove, Tamandaré, State of Pernambuco, Brazil.…”

Population structure and reproductive biology of the crab Sesarma rectum Randall, 1840 (Brachyura, Sesarmidae) in an impacted tropical mangrove in northeast Brazil

“…The sex ratio found in the present study (1 : 0.87) did not differ significantly from the Fisherian proportion of 1 : 1, although there was a trend for males to be slightly more numerous than females. Similarly, Silva et al (2007) found no deviations from the expected ratio for a population of S. rectum in Paraty, Rio de Janeiro, and neither did Silva & Chacur (2002) for S. rectum in Ubatuba, nor Castiglioni et al (2011) for S. rectum in Arinquindá, Pernambuco. However, in these populations there was also a slight trend toward a greater abundance of males.…”

“…However, some authors (Díaz & Conde, 1989;Silva et al, 2007) studied crab populations of impacted areas and observed that sesarmid crabs, as well as panopeids and porcellanids, are able to adapt to adverse conditions due to their phenotypic plasticity (Vergamini & Mantelatto, 2008;Miranda & Mantelatto, 2009).…”

“…Studies of the population biology and reproductive biology of sesarmid crabs are numerous, including S. rectum from subtropical mangroves in southeastern Brazil (Mantelatto et al, 1999;Silva & Chacur, 2002;Silva et al, 2007), but relatively few studies have been carried out in tropical mangroves in Brazil (Castiglioni et al, 2011). Comparisons among populations will help to evaluate the differences between them, as well as to understand the environmental and biological constraints from which those differences originate.…”