Polychaete distribution on the southwestern Atlantic continental shelf

ABSTRACT

Diversity and distribution of polychaetes on the southeastern Brazilian Shelf (SBS) adjacent to the city of Santos were studied. The study area is situated in the vicinity of Santos Bay with its estuarine complex and other small rivers along the coast. A total of 16,274 specimens belonging to 214 polychaete species were found at 21 sampling stations during two different periods. Two communities occur along the shelf and were related firstly to sediment characteristics. Prionospio dayi (Spionidae) was dominant in the inner shelf community that was characterized by well-sorted, very fine sand. The outer shelf community was found in muddy sediments with high organic matter content and was dominated by subsurface deposit feeders, like Petersenaspis capillata (Sternaspidae) and Leitoscoloplos kerguelensis (Orbiniidae), and by large carnivores such as Aglaophamus sp. (Nephtyidae) and Sigambra sp. (Pilargidae). A transition zone of mixed sediments presenting high diversity and richness was found between these communities. The characteristics of bottom water and food quality in the sediment were important to divide the inner shelf into two sub-areas. Nearshore sampling stations (A group) were more influenced by freshwater input, mainly during summer. This influence is not conspicuous at stations close to 30 m depth (B group). However the effect of South Atlantic Central Water mass (SACW) intrusion on the benthic system was observed on the inner shelf – B group during the summer. The summer intrusion of SACW onto the inner shelf may explain the higher quality of organic matter that resulted in an increase in polychaete abundance and richness.

RESPONSIBLE EDITOR:

• Alf Josefson

KEYWORDS:

• Fluvial influence
• polychaete distribution
• SACW
• sediment type

Acknowledgements

The authors thank the Laboratório de Ecologia Bêntica/IOUSP team as well as the crew of R/V Besnard for their laboratory and field support, repectively. MS would also like to thank Professor Edmundo F. Nonato (in memoriam) for his help in the identification of the polychaetes.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Maurício Shimabukuro http://orcid.org/0000-0002-1572-8542

Additional information

Funding

The authors wish to thank FAPESP for the MSc grant to Maurício Shimabukuro (08/557127). This study is part of the multidisciplinary project ‘The influence of the estuarine complex of the Baixada Santista on the adjacent shelf system’ sponsored by FAPESP (Process No. 03/099321) and coordinated by AMS Pires-Vanin.