Abstract
Invasive species are potential threats to biodiversity, especially if they become established and outnumber native species. In this study, a population of the non-indigenous crab Charybdis hellerii was analyzed in an estuary-bay complex on the southeastern Brazilian coast, with respect to its abundance relative to sympatric native brachyuran species, as well as the size structure, sexual maturity, sex ratio, frequency of mutilation, reproductive period, and development of the reproductive system. Crabs were sampled monthly both in the intertidal zone of rocky shores and on sublittoral soft-bottom. Nine species were recorded on the rocky shores, where C. hellerii was the second most abundant species; only three individuals of C. hellerii were collected in the sublittoral samples. This population of C. hellerii showed a unimodal size structure composed mainly of mature individuals; males were larger than females, and the sex ratio was skewed toward males (3.1:1). About 46.9% of the individuals (75 of 160 crabs) had mutilated or regenerating appendages, more frequent in males (56.8%) than in females (28.2%), which may reflect both inter- and intraspecific agonistic interactions. A continuous reproductive pattern is suggested for this population, although ovigerous females occurred unevenly during the year, with 58.82% of them being collected in winter. There was evidence of multiple spawning, since the ovigerous females with an initial egg mass showed mature ovaries as well as seminal receptacles filled with sperm. C. hellerii is well established in the estuary-bay complex, but is concentrated in intertidal and shallow subtidal rocky shores, where it may compete with and replace other species such as the portunid Cronius ruber. This study also highlights the importance of systematic monitoring studies to evaluate the effects of the introduction of non-indigenous species on ecologically similar natives.
Highlights
Many species around the world have successfully colonized new habitats, and this is an ongoing process
A total of 3,887 crabs were collected in the estuary-bay complex during the two sampling periods: 465 from rocky shores and 2422 from subtidal soft-bottom habitats
The relative abundance of species varied over time, with C. hellerii being more abundant than M. nodifrons only in July 2009 (Figure 2)
Summary
Many species around the world have successfully colonized new habitats, and this is an ongoing process. Independent of the introduction pathway, bioinvasions threaten biodiversity (Morán and Atencio 2006). These exotic species may have negative impacts on benthic communities, especially indigenous species (Ferreira et al 2009), leading to loss of biodiversity. Human activities may mediate the global dispersal of species (Barros et al 2009), as the high-intensity human activities in coastal waters, such as shipping (Ruiz et al 1997), organisms transplanted for aquaculture purposes (Kerckhof et al 2007), construction of interoceanic canals (Galil 2000), release of species associated with the pet industry or management practices (Ruiz et al 1997), movement of fouling communities and transport of ballast water (Campos and Türkay 1989; Lemaitre 1995; Torchin et al 2001; Ferreira et al 2009), or marine litter (Derraik 2002). Human-induced global climate change may be a factor in enlarging the geographical range of species (Kerckhof et al 2007)
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