Distribution and frequency of siphonophores (Medusozoa, Hydrozoa) off the Southeastern Brazilian Bight (22°- 28.5°S, Southwestern Atlantic).

ARAUJO E.; OLIVEIRA O.; NASCIMIENTO B.; GENZANO G. N.; MIANZAN H.

Mar del Plata

Simposio; 3rd Jellyfish Blooms Symposium; 2010

INIDEP

Distribution and frequency of siphonophores (Medusozoa, Hydrozoa) off the Southeastern Brazilian Bight (22°- 28.5°S, Southwestern Atlantic) Enilma M. Araujo1,2, Otto M. P. Oliveira3, Karine B. Nascimento3, Gabriel Genzano1, Hermes Mianzan4 1 Estación Costera Nágera, Universidad Nacional de Mar del Plata, Argentina.. 2 CAPES, Brasil (supported by CAPES fellowship), 3CEBIMar – Universidade de São Paulo, Brasil.(Supported by FAPESP and CNPq, Brasil) 4CONICET - INIDEP, Argentina. The Southeastern Brazilian Bight, located between Cape Frio (22°S) and Cape Santa Marta (28°30´S), presents a pelagic environment, characterized by the presence of three water masses and influenced by the Brazil Current, which flows towards the south along the continental slope. Zooplankton diversity and abundance in this area are primarily controlled by the upwelling events of the nutrient rich South Atlantic Central Water in the summer, although secondary nutrient inflows, like some large estuarine outflows, can take an important role in this balance. In this context, we studied the diversity, frequency of occurrence and density of the siphonophores, an important group in the planktonic food webs, formerly neglected in zooplankton studies along this area. We examined samples from 21 sites, collected in May 1976 during the FINEP III Oceanographic Survey, with bongo 500 µm nets in oblique trawls from up to 200m deep to the surface. A total of 32 species were identified. The general density of siphonophores ranged from 0.37 to 9.82 ind./m3, with the predominance of Diphyes bojani (55%), followed by Bassia bassensis (18%), Eudoxoides spiralis (9%) and Abylopsis tetragona (7%). Seven species, including the former four and also A. eschscholtzi, Chelophyes appendiculata and Muggiaea kochi, presented high frequencies (> 76%). The high biodiversity in this area is related to the water mass mixture on the shelf. That also explains the highest frequencies of indicative species of neritic waters, and of the progression of the Brazil Current southwards, as well as typical species of tropical waters with a wide distributions range.