Padrão de distribuição das anêmonas-do-mar (Actiniaria e Corallimorpharia) no Atlântico Sul Ocidental

Abstract

The main objectives of this work tested the hypothesis that Caribbean Sea (and the Antilles) and Southwest Atlantic (SWA): Brazil, Uruguay, and Argentina, differ in shallow water sea anemone species composition and also to explore spatial distribution patterns considering abiotic drivers important to the taxon. A survey of sea anemone records, local and abiotic data (temperature, salinity, and substrate) was performed. We adopted Sørensen dissimilarity, UPGMA, SIMPROF e nMDS to explore clusters regarding sea anemones composition and to estimate richness Chao2 was used. To identify which drivers are more important for the distribution, RDAp was performed. The clusters showed that despite Caribbean Sea anemones being more similar to Brazilian fauna (42%), Brazil and Argentina are very dissimilar (0,88), the three regions form distinct and significative groups with endemism levels that support it (>10%): Caribbean 32,2%, Brazil 21,7% and Uruguay/Argentina 51%. However, Uruguay resides in the same group as Brazil, not Argentina as expected. In Brazil, we found groups that represent North, Northeast, Southeast, South, and Oceanic Islands (CC: 0,88 e MDS stress:0,1). The highest diversity and endemism was found in Southeast group (36 spp. and 48% endemism), followed by Northeast region (22 spp. and 18% endemism). Our inventory represents 70% of knowledge about Brazilian sea anemones (Chao2 = 63,2). The temperature was the most important and influencing factor in Brazilian sea anemone distribution (64% of explanation, p<0,001), followed by salinity (22% and p<0,001). La Plata River altogether with Malvinas Current represents an important barrier for sea anemones in SWA, being responsible for Uruguay+Brazil group and regions dissimilarity, while Amazonas-Orinoco plume seems to act as a filter. Specific features in currents and resurgence system appear to explain high levels of endemism and richness in Southwest Brazil. It is a transition zone between tropical and subtropical Waters with seasonal resurgences, which together with South flow from Brazil current, promotes origin, diversity, and species accumulation. Patterns here found are fit in other biogeographical proposals as Briggs (1974) and decapods system based in the country, which uses temperature and hydrographic characteristics to define their boundaries. Such tendencies are the result of isolation through soft barriers, as well as different ecological tolerances and habitat availability. The results here found are unprecedented for sea anemones in SWA.