Os Nematoda da plataforma continental da região sudeste brasileira sob a influência da Água Central do Atlântico Sul: Cabo Frio (RJ) e Ubatuba (SP) / The Nematoda of the continental shelf of the Brazil\ s southern region under the influence of the South Atlantic Central Water intrusion: Cabo Frio (RJ) and Ubatuba (SP)

Maria Clara Colla Argeiro

Meiofauna is an important component of the marine benthic ecosystem as its densities are usually high in continental shelf sediments and respond quickly to environmental changes. Nematoda is the dominant group among meiofauna organisms, is highly diverse and can be used, as well as meiofauna, as a tool for natural and anthropogenic impacts monitoring. This study is part of the institutional project \" Dynamic of the Continental Shelf Ecosystem of the South Atlantic West Region\". The objective of this project is to study the physics mechanisms that provide the South Atlantic Central Water (ACAS) penetration in the continental shelf and the impact that it causes on the biological processes in two locations: Cabo Frio and Ubatuba. The objectives of this study were: to analyze the composition and structure of the meiofauna community, the associations of families and genus of Nematoda on the inner and outer shelf of Cabo Frio and Ubatuba, as well as its relations to the environmental variables, especially with sediment grain size, phytopigments biomass and water masses characteristics. Samples were taken on two depths (40 and 100 m), in the summer and winter of 2001 in Cabo Frio and in the winter of 2001 and summer of 2002 in Ubatuba. Two 30 x 30 cm boxcorer were used, and from each one two samples were taken with a 4.9 cm2 superficial area and 10 cm height tube corer, for the meiofauna sampling. Meiofauna was separated in higher groups and 200 Nematoda were identified per station. The highest meiofauna densities were found on 40 m during summer in Ubatuba (2001.7±703.1) and on 100 m during summer in Cabo Frio (1010.0±959.0). These benthic responses could be a consequence of the increase of primary pelagic production, in consequence of the intrusion of SACW (South Atlantic Central Water), and its sedimentation in Cabo Frio and Ubatuba, as well as the terrigenous input on the Ubatuba inner shelf. The Nematoda genus composition was related mainly to sediment grain size. Cabo Frio inner shelf, with sandy sediments and constant dynamics was characterized by the dominance of the genera Daptonema (Xyalidae), while outer shelf in the summer in Cabo Frio by the genera Aponema (Microlaimidae), that was associated with phytodetritos and fine sediments. During winter Sabatieria (Comesomatidae) was dominant. Ubatuba stations were characterized by Terschellingia (Linhomoeidae) and Sabatieria (Comesomatidae) on the inner shelf, in summer and winter times. At 100 m depth Desmoscolex (Desmoscolecidae) and Sabatieria (Comesomatidae) were the most abundant genus during winter and summer. The highest genus diversities were observed in Ubatuba, which suggests that diversity may be related to sandy, heterogeneous sediments. Regarding the trophic groups, selective and non-selective deposit feeders were the most abundant on the study area. The multivariate analyses proved that analyses on a genus level allowed a better environmental characterization of the study area, when compared to analyses on the level of family or meiofauna groups.

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