Abstract
An assortment of environmental factors may limit the permanence of hermit crabs in the environment, and determination of certain ecological indices can reveal the current conditions of the assemblage. This study evaluated the assemblage of hermit crabs near two islands adjacent to areas with fishing activity. Hermit crabs were collected monthly near Couves and Mar Virado islands on the southeastern coast of Brazil, from January through December 1998. Environmental factors were also recorded monthly. Ecological indices including species richness, diversity, evenness and dominance were calculated. The environmental characteristics differed between the islands, which helps to explain the differences in the composition of hermit crabs between the locations. Hermit crabs were significantly more abundant near Couves Island, where, according to the canonical correspondence analysis (CCA), the environmental parameters varied less. The Monte Carlo test (P < 0.05) confirmed the CCA model, indicating a strong correlation between the species of hermit crabs, bottom and surface water temperatures, and sediment organic-matter content. The presence of ovigerous females throughout the year indicates that these areas are favorable for reproduction. These results indicate that the environmental heterogeneity allows the establishment of different species of hermit crabs, influencing species richness and abundance of individuals in the ecosystem. These conditions favor the establishment of diverse benthic communities near the studied islands. Keywords : Diogenidae, Paguridae, diversity, abundance, multivariate analysis, Dardanus insignis, Loxopagurus loxochelis .
Highlights
The southeastern/southern Brazilian coast is a hydrological and wildlife transition area, with a combination of biological characteristics and associated fauna originating from tropical, subtropical and subantarctic regions (Sumida and Pires-Vanin, 1997)
The organic-matter content in the sediment was similar near Couves (4.75 ± 2.63) and Mar Virado (3.17 ± 3.12) (Table 1); finer fractions predominated near Mar Virado, while near Couves the sediment contained large proportions of medium and coarse sand (Table 1, Figure 3)
P. diogenes, P. erythrops and P. exilis occurred near both islands, totaling 1116 individuals (Table 2)
Summary
The southeastern/southern Brazilian coast is a hydrological and wildlife transition area, with a combination of biological characteristics and associated fauna originating from tropical, subtropical and subantarctic regions (Sumida and Pires-Vanin, 1997) These features increase the species richness in the region, and the composition of the benthic communities has been widely investigated (e.g. Abelló et al, 1988; Fransozo et al, 1998; De Léo and Pires-Vanin, 2006; Muñoz et al, 2008; Bertini et al, 2010), to aid in the development and strengthening of local preservation practices (McNeely et al, 1990). Costa et al (2005) described the effects on the Brazilian coastal fauna caused by predatory fishing for the shrimp Xiphopenaeus kroyeri (Heller, 1862) This affects the entire benthic ecosystem because of the large amounts of bycatch generated by this trawl fishery (Voultsiadou, 2011). This study investigated the composition and structure of the assemblage of hermit crabs near two islands in southeastern Brazil, aiming to evaluate the ecological indices of hermit crabs present near the islands and the fishing area, as well as the relative abundance of species associated with the environmental characteristics at each site
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