767 



Abstract— The Abrolhos Bank region 

 off the eastern coast of Brazil, under 

 the influence of the Brazil Current, 

 constitutes a typical tropical coral reef 

 ecosystem that is characterized by a 

 high diversity of tropical fish. Results 

 of three ichthyoplankton surveys con- 

 ducted in this region during summer, 

 autumn, and winter revealed that there 

 were two dominant fish groups: meso- 

 pelagic fish and coral-reef-associated 

 fish. From the 45,614 larvae collected, 

 83 taxa (77 families and 6 orders) 

 were identified, in which the family 

 Myctophidae was the most abundant 

 accounting for more than 25% of the 

 total catch in the three cruises. Among 

 the Myctophidae, seasonal variation 

 in abundance of Myctophum affine 

 was significant; there was an out- 

 standing peak in abundance of this 

 species during the summer surveys. 

 The summer peak in abundance of 

 five other species (Diaphus spp., Lep- 

 idophanes gueniheri. M. nitididum, 

 M. obtusirostre. and Hygophum rein- 

 hardtii) was not as pronounced. Larval 

 distribution patterns of these six spe- 

 cies showed no remarkable seasonal 

 change, being evenly distributed over 

 the oceanic area. The coral-reef-asso- 

 ciated fish larvae were confined to 

 the bank and adjacent waters. The 

 spatiotemporal distribution patterns of 

 these larvae was strongly influenced 

 by hydrographic features and some 

 seasonal variation was observed. Four 

 larval fish assemblages were identified: 

 Abrolhos Bank, neritic, transitional, 

 and oceanic assemblages. The Abrolhos 

 Bank assemblage was characterized by 

 coral-reef-associated fish, mainly Gobi- 

 idae, occupying most areas of the bank 

 on the three cruises. The oceanic assem- 

 blage was dominated by mesopelagic 

 fish, especially Myctophidae in all sea- 

 sons and their occurrence was limited to 

 the open ocean. The transitional assem- 

 blage was characterized by a mixture 

 of coral-reef-associated fish and meso- 

 pelagic fish, with a seasonal change of 

 dominant groups. It occupied mainly 

 the shelf break area. The small pelagic 

 fish (sardine and anchovy) were the 

 dominant group of the neritic assem- 

 blage and occupied the coastal region 

 south of the Abrolhos Bank, where the 

 influence of the South Atlantic Central 

 Water was evident. 



Seasonal variation in larval fish assemblages 

 in relation to oceanographic conditions in the 

 Abrolhos Bank region off eastern Brazil 



Ricardo H. Nonaka 



Yasunobu Matsuura 



Kazuko Suzuki 



Institute Oceanografico da Universidade de Sao Paulo 

 Cidade Universitana 

 Butanta, 05508 

 Sao Paulo, Brazil 

 e-mail nonakawusp br 



Manuscript accepted 10 Mav 2000. 

 Fish. Bull. 98:767-784 i2006). 



The tropical marine ecosystem is char- 

 acterized by 1) the presence of coral 

 reefs, which support a large variety 

 of fish communities and benthic fauna 

 that are point sources of eggs and 

 larvae and by 2) the open ocean, where 

 mesopelagic fish dominate the fish com- 

 munity. Thus, the larval fish assem- 

 blages in tropical marine ecosystems 

 are a result of the spawning activities 

 of these two communities (Ahlstrom, 

 1971; 1972; Leis and Goldman, 1987; 

 Flores-Coto and Ordonez-Lopez, 1991; 

 Leis, 1993). The formation of larval fish 

 assemblages is mainly influenced by 

 the reproductive cycles of the adult fish 

 populations. The seasonal cycle of fish 

 spawning activities in the tropics is not 

 pronounced because of a low level of 

 variation in environmental conditions 

 (Lowe-McConnell, 1987). 



Distribution patterns offish larvae in 

 any region of the ocean are related to the 

 reproductive activity of the adult pop- 

 ulation and to topographic and hydro- 

 graphic features that affect the dispersal 

 of the lai-vae. A study of the distribution 

 patterns of fish larvae contributes to 

 an understanding of the interrelation- 

 ships among fish species during their 

 early life stages, as well as an under- 

 standing of adult spawning patterns. In 

 addition, information can be obtained 

 on the reproductive strategies adopted 

 by these fish in response to the phys- 

 ical and biological processes of the 

 region. Distribution patterns among 

 ichthyoplankton species arise from the 

 synchronous reproductive activities of 

 different species that are developed 

 during evolutionary adaptation to geo- 



graphic and oceanographic conditions. 

 This information is important for a 

 rational use of fishery resources and 

 also for an understanding of the ecolog- 

 ical status of the component species in 

 a marine ecosystem. 



Ichthyoplankton surveys in Brazil- 

 ian waters are concentrated off south- 

 ern Brazil (Matsuura and Olivar, 1999); 

 only a small number of sampling cruises 

 have been conducted off the eastern 

 coast (Aboussousan, 1969; Matsuura, 

 1985). 



In our study, temporal and spatial 

 changes in larval fish assemblages in 

 relation to physical processes of the 

 Abrolhos Bank region were examined. 

 Particular emphasis was placed on the 

 seasonal variation of larval fish assem- 

 blages of abundant fish taxa. The objec- 

 tive of the present study is to understand 

 the origin and maintenance of these 

 larval fish assemblages and their rela- 

 tion to oceanographic conditions. 



Materials and methods 



Three survey cruises were conducted 

 along the eastern coast of Brazil. Two 

 cruises of the FINEP Project (FINan- 

 ciadora de Estudos e Projetos) were 

 made with the RV Prof. W. Besnard in 

 June and November-December of 1978. 

 Sixty-four stations between latitudes 

 17°S and 23°S were sampled with a 

 Nansen bottle containing a reversing 

 thermometer for hydrographic data and 

 with Bongo nets for collecting zooplank- 

 ton. The third cruise, that of the JOPS 

 II-9 (Joint Oceanographic ProjectS-II, 



