Structure and dynamics of benthic megafauna on the continental shelf offshore of Ubatuba, southeastern Brazil

Abstract

Twelve survey cruises on the continental shelf offshore of Ubatuba, southeastern Brazil, were conducted during 1985 to 1987 as a part of a broad oceanographic investigation on the tropical Atlantic shelf ecosystem. Two different water masses influence the seabed: South Atlantic Central Water (SACW) and Coastal Water (CW). The first penetrates towards the coast during summer months, and retreats offshore in the winter. Distribution, density and biomass of the benthic megafauna show 2 domains: inner shelf and outer shelf, both separated by a front. High abundance of the brachyuran crab Portunus spinicarpus characterizes the frontal system and occasionally changes the structure of the inner and outer shelf assemblages. Mulhvariate analyses showed that water masses and sea depth are the main factors structuring the benthic megafauna comn~unities. Clustering analysis disclosed 4 dlstinct faunistic assemblages: (1) coastal communities withln the CW domain, (2) inner shelf communities influenced by a mixed zone with CW predominant, (3) frontal zone communities where SACW was predominant, (4) outer shelf communities within the SACW domain. Species diversity was almost hon~ogeneous on the entire shelf except in the frontal zone where it sharply decreased. The common species, both perenial and seasonal, showed a consistent pattern of d o m a n c e through the study period. Adjustments occur within the community whereby some species increase in abundance when others decrease, maintaining a stable pattern. A 'cyclic' stability-adjustment mechanism is proposed to explain the dynamics of the megabenthos in the Ubatuba region.

Population structure of the swimming crab Achelous spinicarpus (Crustacea, Portunoidea) in São Paulo northern coast, Brazil

“…However, a different pattern was also observed by Ogawa and D'Incao (2010) for A. spinicarpus, who collected samples from 10 to 100 m in depth and described females with mean sizes larger than males. The results described by Sanvicente-Añorve et al (2008), who collected this species in the Gulf of Mexico (unspecified depths), indicate similar mean size between males and females.…”

“…This is common in populations with very high densities, such as A. spinicarpus, which was the second most abundant Brachyura species in Ubatuba and the first in Caraguatatuba (Braga et al, 2005). Populations of this species can occur at so high densities in some depths that, according to a study by Pires (1992), in the Ubatuba region, A. spinicarpus comprised about 90% of the megafauna in areas affected by the water mass South Atlantic Central Water.…”

“…In contrast, the Caraguatatuba littoral area (23° 36' -23º 40'S, 45º 07' -45° 25'W) presents a more homogeneous variation of these same environmental factors, because it is sheltered from the direct action of the waves and winds by the São Sebastião Island, showing bottom morphology with slightly variations (Barros et al, 1997). These areas are influenced by three water masses that, when compared to each other, have peculiar characteristics and distinct models of distribution throughout the year (Pires, 1992): Coastal Water (Temperature > 20 °C and Salinity < 36), Tropical Water (T > 20 °C and S > 36), and South Atlantic Central Water (T < 18 °C and S < 36) (Castro-Filho et al, 1987).…”

“…According to Pires (1992) and Andrade et al (2015a), this water mass may affect the dynamics of decapod crustacean assemblages, so that their population structure (Andrade et al, 2015b).…”

“…The swimming crab A. spinicarpus is considered a bioindicator of cold water masses (Pires, 1992;Lima et al, 2014), such as the appearance of the South Atlantic Central Water (SACW) in southeastern coast of Brazil, which causes an increase of nutrients in the region, favoring primary production. According to Pires (1992) and Andrade et al (2015a), this water mass may affect the dynamics of decapod crustacean assemblages, so that their population structure (Andrade et al, 2015b).…”