The Brachyura and Anomura fauna ( Decapoda ; Crustacea ) in the Arvoredo Marine Biological Reserve on the southern brazilian coast

Eight species of Brachyura and two species of Anomura were registered for the first time on the Santa Catarina coast, in the waters around the Arvoredo Marine Biological Reserve. The animals were collected by scuba divers, between 3 and 22 meters depth, from September 2001 to February 2003. A total of 31 decapod species were collected, and most of the new occurrences had already been registered in the adjacent northern waters.


Introduction
The review of Lana et al. (1996) showed that benthic crustaceans were poorly studied on the Santa Catarina coast.A complex current, wind and water mass interaction improves the transport of organisms from tropical, subtropical or even subantarctic areas to the southern coast (Borzone et al., 1999).The species diversity in the Arvoredo Archipelago is the result of the occurrence of tropical and subtropical fauna and recent works have been quantifying these species.Among the ten species of sponges that occurred in the area, four were registered for the first time on the Brazilian coast (Lerner, 1996).In addition, seventeen mollusk species were registered for the first time on the Santa Catarina coast (Wiggers and Magalhaes, 2003).The unique coralline red algal bed (Corallinaceae, Rhodophyta) of the Brazilian southern coast occurs in the main island, where 5 non articulated coralline algae species were registered for the first time in southern waters (Horta, 2000).
There is no scientific report about the crustaceans of the Arvoredo Biological Marine Reserve (Reserva Biológica Marinha do Arvoredo, RBMA) (27° 17' 7'' S and 48° 25' 30'' W).However, fishermen and divers usually find shrimps, crabs and lobsters which are illegally captured in the area.
The present work aims to survey the fauna of Brachyura and Anomura in the Arvoredo Biological Marine Reserve.The management plan of the marine reserve has been established after our samplings.It would be possible from now on to follow the changes in the species richness after the improvement of the new activites in the area.

Material and Methods
The studied area is close to the Subtropical Convergence (33-38° S), where the Brazilian Current flowing to the south reaches the Malvinas Current, which flows to the north.The South Atlantic Central Water (SACW) is formed in the area of the Convergence and circulates in the South Atlantic Ocean (Silveira et al., 2001).In the Arvoredo Archipelago area the SACW occurs at 20 m depth and the Tropical Shelf Water dominates the surface waters (Chludinski and Bonetti, 2002).

Results and Discussion
Salinity and temperature data varied from 30 to 36.5‰ and 16.5 to 23 °C, characterizing the presence of Tropical Water and South Atlantic Central Water or Subtropical Water (Emilson, 1959).
A total of thirty one species were collected in the area (Table 1), being 2 Paguridae, 2 Diogenidae and 2 Porcellanidae (Anomura) and most of the Brachyura were Majidae and Xanthidae.Five species of Majidae, one Goneplacidae, one Dromiidae, one Pinnotheridae, one Paguridae and one Diogenidae, comprising 10 spe-cies, were registered for the first time on the Santa Catarina coast, in the waters around the Arvoredo Marine Biological Reserve (Table 1).
According to the crustacean biogeographic division of South America, Arvoredo Island is located in the Paulista Province (Coelho et al., 1980).Eight species had been previously registered up to São Paulo (Melo, 1996), in the Paulista Province and one in Espírito Santo, which is in the Brazilian Zoogeographic Province (Coelho, op.cit.) and now have their distribution expanded to Santa Catarina.Paguristes robustus Forest and Saint Laurent, 1967, was previously recorded in the Argentinean Province; this occurrence should be related to the influence of the cold waters in the area.Costa (1968) apud Palácio (1982), working with Brachyura, showed a faunistic change between the Abrolhos Archipelago and Cape Frio and another change between São Paulo and Santa Catarina.Patterns of marine species distributions are influenced and limited by frontiers that are very difficult to detect (Melo, 1985).The new occurrence of these species in the Arvoredo area, close to septentrional limit of the tropical fauna of the Paulista Province and the northern limit of the Argentinean Province was already expected with the increase of the samplings.
Marine invertebrate surveys along the Brazilian coast are mainly conducted from otter trawls of fishing boats, oceanographic vessels or snorkeling.Eighty six Brachyuran species and twenty seven Anomuran species have already been complied by Melo (1996 and1999) on the Santa Catarina coast and could be found around Arvoredo Island.However, scuba sampling efforts improve the capture of hidden animals in crevices or under rocks.Some species, including some of the new records (Table 2), were collected associated to the rhodoliths.The presence of the rhodoliths was the main force to the structure of the benthic macrofauna community in the algal bed of the Arvoredo Island (Blankensteyn et al., 2003).We could not find other studies in the literature where only scuba-diving was used to sample crustaceans along the Brazilian coast.Crabs were in general very hard to find, especially dur-ing the day.Most of the time, after 50 minutes searching, we returned on board with two or three different species.
There was almost one new record of decapod species in the area per dive (10 new records in 15 dives).27° 17' 7'' S and 48° 25' 30'' W), new occurrences in Santa Catarina and previous distribution along the Brazilian coast.Calappa gallus Herbst, 1803, was collected only during the night sample in the coralline red algae bed.Its carapace was completely encrusted with the coralline algae and the animals were moving fast over the rhodoliths.Calappa philargius Linnaeus, 1758, had also shown night activity along the eastern coast of Thailand and this behavior would prevent the algal encrustation (Becker and Wahl, 1996).However, epibiontic encrustation is also considered a positive interaction, like crab camouflage (Coutress et al., 1970 apud Becker andWahl, 1996;Maldonado and Uriz, 1992).The pagurids Rhodochirus rosaceus A. Milne Edwards and Bouvier, 1893 and Dardanus arrosor Saussure, 1858, were freely moving during the day over the rhodoliths but only the shells inhabited by R. rosaceus had coralline algal encrustation.

Species
Porcellana sayana Leach, 1820, has a symbiotic relationship with pagurids (Melo, 1999) and this species was registered on the shells inhabited by Dardanus arrosor insignis, and not in the abdomen as expected.Stenorhynchus seticornis Herbst, 1788, was easily observed, moving and jumping slowly under the rocks.Mithraculus forceps A. Milne Edwards, 1875, and Mithrax tortugae Rathbun, 1920, were very common inside the rhodoliths.
Scuba diving proved to be a very good option to sample the sea bottom without destruction of the whole environment and to search for animals hidden in microhabitats.Thus, amending the previous scarce sampling along the Santa Catarina coast, ten new records for the area have now been added, with the expansion of the distribution of these species.

Table 1 .
Decapods registered in the area of Arvoredo Island (