POLYCHAETE ASSEMBLAGES IN SOFT SEDIMENTS NEAR A SUBTIDAL MACROALGAE BED AT ARRAIAL DO CABO (RIO DE JANEIRO, BRAZIL)

Almeida, T. ¹ & Ruta, C. ²

¹ Instituto de Estudos do Mar Almirante Paulo Moreira, Rua Kioto, 253, Praia dos Anjos, Arraial do Cabo, 28930-000, Rio de Janeiro, RJ, Brazil

² Departamento de Zoologia, Universidade Federal do Rio de Janeiro, Brazil

There is variation in the distribution of organisms and environmental variables at different spatial scales. Polychaete annelids belong to a faunal group that has an important relationship with different marine substrata. The aim of this investigation was to know whether the presence of the Sargassum furcatum bed influenced the polychaete community structure in the adjacent sediments. This study was conducted on a subtidal sandy beach, at a depth of 3 - 6 m, in the northern coast of Rio de Janeiro (230S, 42001'W). Our results showed that the polychaetes were well represented numerically - approximately 20% of all specimens sampled. At this site, there is a S. furcatum bed (3.5 m depth) that influenced the structure of neighboring soft bottom communities. Three to ten replicate samples were collected at six adjacent points (at distances of 30 - 90 m from the bed). They were collected with plastic core tubes (15 cm diameter, 15 cm deep), 0.02m2 in surface area, one at each point. Additional samples of each point were collected to characterize the sediment's granulometry and to determine the concentration of organic carbon and nitrogen. Extraction of macrofauna from the sediment was achieved by using a sieve (mesh size 0.5mm). Two sets of 10 replicates were taken to test the minimal number of replicates to polychaetes species. A total of 262 specimens, distributed by 21 species, was accounted. Aricidea (Allia) cf. albatrossae, Armandia longicaudata and Kinbergonuphis tenuis were the most abundant species. Densities varied from 6.67 to 17.67 indiv./0.02m2 ; Shannon-Wienner diversity (H') varied from 0.35 to 2.00; and evenness (J) varied from 0.25 to 0.90. The first two axes of factor correspondence analysis were responsible for 58.5 and 37.7 % of the total system variation. Three polychaete associations were identified, and found to be related to the presence of the S. furcatum bed. Despite the proximity of the sample points, depth variation and granulometric parameters, the presence of a Sargassum bed was an important structuring factor for polychaete associations in the area studied.