Structuring Factors Of The Cumacean Communities Of The Continental Shelf Of Southeastern Brazil

BRAZILIAN JOURNAL OF OCEANOGRAPHY, 62(2):103-116, 2014 STRUCTURING FACTORS OF THE CUMACEAN COMMUNITIES OF THE CONTINENTAL SHELF OF SOUTHEASTERN BRAZIL Pedro Abib Cristales and Ana Maria S. Pires-Vanin Instituto Oceanográfico da Universidade de São Paulo (Praça do Oceanográfico, 191, 05508-120 São Paulo, SP, Brasil) *Corresponding author: http://dx.doi.org/10.1590/S1679-87592014056206202 ABSTRACT Cumaceans are benthic crustaceans distributed worldwide, from intertidal to abyssal plains. They live in sandy and muddy bottoms and can sometimes be found in the water column. Despite their ecological importance as food items for fishes and other organisms and their usefulness as environmental indicators, very few studies have investigated their biodiversity and distribution in Brazil. The present paper reports an ecological study of the cumacean species found on the continental shelf off Santos, southeastern Brazil. It investigates the composition and spatio-temporal structure of the communities, the main environmental factors responsible for the maintenance of that structure and analyzes the effects of the seasonal oceanographic changes on the community descriptors. A grid of 21 stations located between 10 and 100 m depth was created in winter 2005 and summer 2006 and the sediment samples collected with a 0.1 m2 box corer. Twenty four species were obtained, five of them being the most numerous: Diastylis sexpectinata, D. sympterygiae, Eudorella sp., Oxyurostylis salinoi and Anchistylis notus, the latter highly dominant in summer. Diastylis sympterygiae was characteristic of the shallowest and least saline stations (< 16 m depth; S = 33.07 - 34.2) in both seasons. Of the total of 919 individuals, nearly 70% occurred in summer. The area was divided into four depth bands and no significant temporal difference was found as regards the density distribution of cumaceans in those bands as between the samples of the two campaigns. There were, however, spatial differences within bands in the summer campaign: the higher values of density, diversity and richness were close to the 50 m isobath in both campaigns, a fact that could well be attributed to the ongoing effect of the South Atlantic Central Water in this area. The results showed also that depth and the sediment particle size were the main structural factors determining the composition and distribution of the cumacean species. RESUMO Cumáceos são crustáceos peracáridos cosmopolitas que se distribuem desde a zona entre marés até os fundos abissais. Habitam fundos arenosos e lamosos e eventualmente são encontrados no ambiente pelagial. Apesar de sua importância na dieta de diversos organismos, e de serem considerados bons indicadores ambientais, poucos estudos ecológicos foram realizados com o grupo no Brasil, não havendo uma avaliação do papel que desempenham na estruturação e funcionamento do ecossistema bêntico. O presente trabalho teve como objetivo descrever a composição e a distribuição espaço-temporal das espécies de Cumacea, investigar a existência de comunidades e de sua estrutura, identificar os principais fatores responsáveis pelos agrupamentos encontrados e avaliar o efeito das mudanças sazonais da estrutura oceanográfica sobre os descritores utilizados. Para tanto duas campanhas foram realizadas, no inverno de 2005 e no verão de 2006, em uma grade de 21 estações situadas na plataforma continental sudeste ao largo de Santos, dispostas em quatro faixas de profundidade (entre 10 e 100 m) e amostradas por meio de box corer com 0.1 m2 de área amostral. Do total de 24 espécies encontradas, cinco foram as mais abundantes: Diastylis sexpectinata, D. sympterygiae, Eudorella sp., Oxyurostylis salinoi e Anchistylis notus, esta última altamente dominante no verão. Diastylis sympterygiae foi característica das estações rasas (< 16 m) e com salinidades baixas (33.07 - 34.2), tanto no inverno quanto no verão. Do total de 919 indivíduos obtidos pouco mais de 70% ocorreu no verão. A área foi dividida em quatro faixas de profundidade e, considerando a distribuição da densidade de cumáceos nessas faixas, não foi encontrada diferença temporal significativa entre as amostras das duas campanhas. Entretanto, houve diferença espacial entre as faixas na campanha de verão, sendo os valores mais elevados de densidade, diversidade e riqueza situados próximo à isóbata de 50 m em ambas as campanhas, podendo ser atribuídos ao efeito contínuo da Água Central do Atlântico Sul sobre essa área. Os resultados mostraram ainda que a profundidade e as características granulométricas do sedimento foram os principais fatores estruturadores das comunidades de Cumacea e determinantes da composição e distribuição das espécies na área. Descriptors: Cumacea, Distribution, Benthic community structure, Santos, Continental shelf. Descritores: Cumacea, Distribuição, Estrutura de comunidades bênticas, Santos, Plataforma continental. 104 ECOSAN), 2014 BRAZILIAN BRAZILIAN JOURNAL JOURNALOF OF OCEANOGRAPHY, OCEANOGRAPHY,62(2), 62(special 2014 issue BRAZILIAN JOURNAL OF OCEANOGRAPHY, 62(special issue ECOSAN), 2014 INTRODUCTION Cumaceans are peracarid crustaceans, mainly marine, distributed worldwide from intertidal to abyssal plains (JONES, 1976). They inhabit sandy and muddy bottoms, and are sometimes found in the pelagic environment (ANGER; VALENTIN, 1976; MACQUART-MOULIN, 1991). They can also occur in association with seaweeds and bryozoans, (ALFONSO et al., 1998; CONRADI et al., 2000) and in whale carcasses and hydrothermal vents (SMITH, 2003; CORBERA; SEGONZAC, 2010). Despite their importance as food item for many organisms (BĂCESCU; QUEIROZ, 1985; SUTHERLAND et al., 2000), and as initial colonizers of dafaunated sediments (SANTOS; SIMON, 1980), their great abundance in some areas and their role as environmental indicators (CORBERA; CARDELL, 1995; SWAILEH; ADELUNG, 1995), few ecological studies have described the importance of environmental parameters in the distribution and composition of cumacean communities (WATLING; GERKEN, 2005; MARTIN et al., 2010). Most studies in Brazil have focused on the taxonomy of the group (e.g. BRUM, 1966; BĂCESCU; PETRESCU, 1990; ROCCATAGLIATA, 1997) and only one has addressed its ecology (SANTOS; PIRES-VANIN, 1999). The lack of specialists seems to be the main cause of the slow progress made as regards the group’s taxonomy, and few studies addressing benthic macrofauna in Brazil include cumaceans. In this context, the continental shelf off Santos, situated in the Southeastern Atlantic, has been the object of an interdisciplinary study outlined to evaluate the influence of the estuarine complex of the Baixada Santista on the adjacent continental shelf. The present paper is part of the studies on the benthic fauna and reports the composition and spatio-temporal distribution of the cumacean species on the continental shelf off Santos. The study evaluates the structure of the communities, as well as the interactions between th (...truncated)