Factors affecting seasonal variations in demersal fish assemblages at an ecocline in a tropical–subtropical estuary

Abstract

Seasonal changes of fish species composition in terms of biomass, density and number of species in three areas of the main channel of the Paranagu´a Estuary (axis east-west) are described in relation to seasonal fluctuations in salinity, water temperature and dissolved oxygen in the main channel. Two hundred and thirty-four samples were collected monthly, between July 2000 and June 2001, in the main channel. Seventy-nine species of 29 families were captured with a total estimated mean density and biomass of 1513 individuals ha À1 and 34 kg ha À1 , respectively. The number of species and total mean density differed significantly among areas and seasons, but the total mean biomass differed only significantly throughout the ecocline (areas) of the Paranagu´a Estuary. For the most abundant species, the mean densities of Stellifer rastrifer, Aspistor luniscutis, Menticirrhus americanus, Sphoeroides testudineus, Cynoscion leiarchus and Symphurus tesselatus (with the exception of Cathorops spixii and Genidens genidens) differed significantly among seasons. The mean biomass of these species, with the exception of G. genidens, S. rastrifer, A. luniscutis and S. testudineus, also differed significantly for the factor seasons. Area was a significant factor for the eight most abundant species (density and biomass), except S. testudineus (density), G. genidens, C. leiarchus and S. tesselatus (biomass). The season v. area interaction term was significant for C. leiarchus (density). Most of these differences occurred during the rainy season when fishes concentrated principally in the middle of the estuary, where the salinity remained stable. It is suggested that the salinity stability in the middle of the estuary is the main reason why the most estuarine resident fish species move downstream and remain there, regardless of the increased freshwater runoff. Moreover, canonical correspondent analysis output detected that during the late rainy season, the variable dissolved oxygen (P < 0Á01) was the most important environmental variable, responsible for structuring patterns of fishes assemblages in the west-east axis of Paranagu´a Estuary. During the end of the ‡Author to whom correspondence should be addressed. Tel. and fax: þ55 8121268225; dry season, both salinity (P < 0Á01) and dissolved oxygen (P < 0Á05) were responsible for this ecological feature in the estuary. Finally, it was possible to detect that juveniles and adults of some important species respond differently to seasonal fluctuations of the ecoclinedetermining environmental factors. This behaviour is suggested as a strategy to avoid competition and predation during the rainy season in the middle estuary. The Paranagu´a Estuary did not fit with the pre-existing models described in the tropical and subtropical estuarine fish literature since its main channel fish assemblages remained within its bounds even during the rainy season.

Estuarine ichthyofauna of the Paraguaçu River, Todos os Santos Bay, Bahia, Brazil

“…The bottom nets accessed the ichthyofauna from the main channel dominated by Ariidae and Sciaenidae around all the Paraguaçu channel (lower estuary), similar pattern to Caeté River estuary, Northern Brazil (Barletta et al 2005), Sepetiba Bay, South-East Brazil (Azevedo et al 2002) and Paranaguá estuary, Southern Brazil (Barletta et al 2008). Although, in the middle estuary, using bottom nets, the dominant family was Sciaenidae with Stelifer rastrifer and Cynoscion microlepidotus showing higher catches and greater constancy of occurrence.…”

“…Caranx latus Agassiz, 1831, Chloroscombrus chrysurus (Linnaeus, 1766), Polydactylus virginicus (Linnaeus, 1758), Pellona harroweri, Harengula clupeola (Cuvier, 1829), Opisthonema oglinum (Lesueur, 1818) and adults of Macrodon ancylodon (Bloch & Schneider, 1801) and Isopistus parvipinis (Cuvier, 1830)). It's accepted that this movement toward middle estuary may be due to the increased salinity in this region, and in turn the estuary did not show the three zones (upper, middle and lower) with salinity gradient set for estuaries of Brazil as shown by Barletta et al (2005Barletta et al ( , 2008 evaluating these saline conditions. The Biota Neotrop.,vol.…”

Population biology of Stellifer rastrifer, S. brasiliensis and S. stellifer in Caraguatatuba Bay, northern coast of São Paulo, Brazil

“…Stellifer rastrifer was not only the most abundant species of its genus but also of its family (Sciaenidae), in addition to being one of the most important in Caraguatatuba Bay (unpublished data) as in other Brazilian areas (GIANINNI; PAIVA- FILHO, 1990a;SANTOS et al, 2002;BARLETTA et al, 2005BARLETTA et al, , 2008CAMARGO;ISAAC, 2005). Monitoring species relative abundance, especially the numerically important ones, may provide important information about environmental changes.…”

“…MENEZES, FIGUEIREDO, 1980), is rarely caught in numbers sufficient to permit this kind of research (BARLETTA-BERGAN et al, 2002;BARLETTA et al, 2003BARLETTA et al, , 2005BARLETTA-BERGAN, 2009;CAMARGO;ISAAC 2005;SCHWARZ et al, 2006). Stellifer rastrifer is found all along the Brazilian coast, in waters of from intermediate to high salinities and low to intermediate depths PAIVA-FILHO, 1990a;SANTOS et al, 2002;BARLETTA et al, 2005BARLETTA et al, , 2008 LOBÃO DE SOUZA 2006).…”

The Use of Non-reef Habitats by Brazilian Reef Fish Species: Considerations for the Design of Marine Protected Areas

“…Moreover, these few protected areas are in many cases too distant (> 400 km) from each other (Floeter et al 2006), reducing their effectiveness due to low connectivity. Although reported worldwide (Cowen et al 2002), the dynamics of inter-habitat connections is practically unknown along the Brazilian coast (Barletta et al 2008). …”