Biodiversity and dynamics of ichthyic communities in the mangrove of Guaratuba, Brazil.

The Bay of Guaratuba, whose area is approximately 45 km(2), is a basin, sit uated to the south of Brazil (25 degrees 52' S; 48 degrees 39' W) and conne cted to the Atlantic ocean. In its northern part, a region of mangrove is f ound, under the influence of seasonal fluvial contributions, dominated by L aguncularia racemosa. The depth exceeds 6 m in some places. According to th e period of the year, salinity varies between 3 and 37, and temperature bet ween 15 and 28 degrees C. Several of the present fish species are exploited by commercial and recreational fisheries. This work describes characterist ics of the fish populations occupying this mangrove, and temporal and spati al evolution of populations of the main species from available data on thei r biology. Between September 1993 and August 1996, fish samplings have been undertaken monthly by trawl, according to the same fishing effort (20 min) , in channels of this ecosystem. Size, numerical abundance and weight of ea ch individual of species were measured, as well as surface and bottom tempe ratures and bottom salinity. Species richness, Shannon-Weaver's diversity i ndex were calculated and abundances were processed by the multivaried analy sis. The global species richness is 61 species, distributed in 28 families; the better represented species are Sciaenidae (10), Gerreidae (5), Carangi dae (5), Ariidae (4), Haemulidae (3), Serranidae (3), Bothidae (3). Each ye ar, the number of species varies between 41 and 44, and a group of eight sp ecies represents between 80 to 90 % of the density and 75 % of the biomass. The constancy of this dominance is the main characteristic of this fish as semblage. The most represented species in abundance is Pomadasys corvinaefo rmis is the first two years, then Stellifer rastrifer. The group of eight m ain species is shared by 15 species in total, of which 13 for the density a nd 14 for the biomass. The most important monthly catches take place in win ter season, during which one observes a decrease of water temperature and a n increase of salinity. These species, however, being likely to be replaced by others according to the year or the season; one never finds the same co mposition in the assemblage which pre serves always the same structures. Se asonal differences between seasons under marine (winter) and continental (s ummer) influences play a major role on the dynamics of fish in the Guaratub a mangrove. This ecosystem plays a functional role in the achievement of th e life cycle of many permanent or temporary species. Those having succeeded to reach high levels of abundance are not represented in a uniform way in the course of the year, even when they reside permanently in the ecosystem. Periodic displacement strategies for self regulation of stocks abundance, are necessary mechanisms for these populations. which thus success to coexi st in occupying the mangrove. (C) Elsevier, Paris / Ifremer / Cnrs / Ird.