Cephalopod paralarvae around tropical seamounts and oceanic islands off the north-eastern coast of Brazil

Abstract

Early life cephalopod stages were collected around tropical seamounts and oceanic islands off the north-eastern coast of Brazil. A total of 511 specimens was caught with oblique Bongo net hauls between 150 m depth and the surface during a joint Brazilian/German oceanographic expedition with the RV VICTOR HENSEN in January/February 1995. Mean density of cephalopods was low with 24 ind 1000 m−3. Fifteen families representing at least 21 genera, from which 11 species were identified. The findings revealed a typical tropical and oceanic cephalopod assemblage. The most abundant families were Enoploteuthidae (27.6%), Ommastrephidae (20.9%), Onychoteuthidae (11.2%), Cranchiidae (10.4%) and Octopodidae (9.2%). Less abundant families were Octopoteuthidae, Thysanoteuthidae, Cthenopterygidae, Lycoteuthidae, Mastigoteuthidae, Tremoctopodidae, Argonautidae, Chiroteuthidae and Bolitaenidae. Highest cephalopod densities occurred along the Fernando de Noronha Chain (34 ind 1000 m−3). Small-sized Enoploteuthidae and Onychoteuthidae dominated in that region. Around the North Brazilian Chain overall cephalopod density was 31 ind 1000 m−3 where again, Enoploteuthidae were most abundant, closely followed by Ommastrephidae. Cephalopod abundance was the lowest (13 ind 1000 m−3) around the St. Peter and St. Paul Archipelago. However, cephalopod diversity was highest in this region (17 genera) with Enoploteuthidae dominating, followed by Cranchiidae. Cephalopod mantle lengths (ML) ranged from 0.8 mm to 25 mm. The majority of specimens were small-sized with 65% below 3 mm ML, and 81% below 4 mm ML. All major genera and species are illustrated and their meso-scale distribution patterns are discussed. The results provide new information on the species composition and distribution patterns of early life cephalopods in tropical seas.