BRAZILIAN JOURNAL OF OCEANOGR., 52(1):47-58, 2004
TEMPORAL VARIATION IN FISH ASSEMBLAGE COMPOSITION ON A TIDAL FLAT Henry L. Spach* ; Rodrigo S. Godefroid; César Santos; Roberto Schwarz Jr. & Guilherme M. L. de Queiroz Centro de Estudos do Mar da Universidade Federal do Paraná (Caixa Postal 50002, 83255-0000, Pontal do Sul, PR, Brasil) *e-mail:
[email protected]
A BSTRACT Annual variation in the fish assemblage characteristics on a tidal flat was studied in coastal Paraná, in southern Brazil. Fish were collected between August 1998 and July 1999, during the diurnal high tide and diurnal and nocturnal low tide of the syzygial (full moon) and quadrature (waning moon) tides, to characterize temporal change in assemblage composition. A total of 64,265 fish in 133 species were collected. The average number of species and individuals, biomass, species richness, diversity (mass) and equitability varied significantly over time . The dissimilarity of the assemblage was greatest in August, September and October in contrast with the period from November to January, with the lowest dissimilarity. The combined action of water temperature, salinity and wind intensity had a great influence over the structure of the fish assemblage.
R ESUMO Os peixes de uma planície de maré da praia Balneário de Pontal do Sul, Paraná, foram coletados, na preamar diurna e na baixa-mar diurna e noturna das marés de sizígia e de quadratura, visando caracterizar as mudanças temporais entre agosto de 1998 e julho de 1999. As coletas totalizaram 64.265 peixes de 133 espécies. Foram observadas diferenças significativas na captura média em número de espécies e de peixes, peso total e nos índices de riqueza, diversidade (H’ peso) e eqüitatividade entre os meses de coleta. A dissimilaridade da ictiofauna foi maior entre os meses de agosto, setembro e outubro em comparação com o período de novembro a janeiro. A ação combinada da temperatura da água, salinidade e intensidade do vento, influenciaram mais sobre a estrutura da assembléia de peixes. Descriptors: Fishes, Tidal flat, Estuary, Temporal variation., Southern coast, Brazil Descritores: Peixes, Planície de maré, Estuário, Variação temporal,.Costa sul, Brasil
INTRODUCTION Few teleosts complete their entire life cycle in estuaries; most are seasonal members of the estuarine communities or merely pass through, migrating between feeding and spawning areas (Potter et al., 1986). In estuaries few species are numerically dominant, and those few dominant species tend to be widely distributed, reflecting the great tolerance and variation of adaptations of these organisms (Haedrich, 1983). Depending upon their way of life in the estuaries, the fish can be either inhabitants of shallow waters, pelagic or epibenthic (Day Jr. et al., 1989). Inhabitants of these shallow waters live on the edges of the estuaries, in salt marshes, tidal creeks, tidal flats and tidal pools. They are generally very small and most do not migrate. “Tidal flats” are shallow-sloped coastal areas of marine sediments that are exposed and submerged regularly by tides. These flats represent a transition zone between terrestrial and marine environments, as
they are generally limited to narrow strips between marshes or mangroves and the sea (Reise, 1985). The shallow estuarine areas have a large number of individuals and species (Hamilton & Snedacker, 1984) and are considered important for the recruitment and breeding of fish (Reise, 1985). The distribution of organisms in estuarine environments is influenced, mainly, by salinity, temperature and dissolved oxygen. Nevertheless, interspecific competition and predation are also important (Kennish, 1990). Due to the morphologic characteristics of a tidal flat, the community is also affected by the climate of the region, the geomorphology of the environment, the inclination of the coast, the width of the tide, the tidal cycle, wave action and tidal currents (Reise, 1985). Little information exists on the ichthyofauna of the shallow marginal areas of Paranaguá Bay (Godefroid et al., 1997; Santos, et al., 2002; Vendel, et al., 2003), especially with relation to the tidal flats, even though they are considered important regions for the recruitment and breeding of fish (Reise, 1985).
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BRAZILIAN JOURNAL OF OCEANOGRAPHY, 52(1), 2004
Therefore, the present study seeks to provide information about the temporal variation in the composition and abundance of the fish assemblage in a tidal flat, located in the euhaline section of Paranaguá Bay.
MATERIAL AND METHODS Study Area The study area is a tidal flat in Pontal do Sul Resort Beach (Fig. 1), located at the southern entrance to Paranaguá Bay (25o20' - 35'S and 48o20' 45'W). Due to its geographical location, this tidal flat suffers influence from both the estuarine environment and the adjacent marine environment, presents a shallow slope and forms a narrow sediment strip between the continent and the sea. This environment may be divided into three distinct regions. The first is
always submerged even during low tide and has a sandy to muddy sediment; next, the middle region, is the actual tidal flat, submerged periodically during the high tide and comprises a sandy sediment; the third region remains exposed most of the time and also has a sandy sediment. Sampling Design Fish were collected during the diurnal high tide and diurnal and nocturnal low tides of the syzygial (full moon) and quadrature (waning moon) tides, between August 1998 and July 1999. Two tows were made in the same direction as the current, at a maximum depth of 1.70 m along a 100 m transect parallel to the tidal flat, separated by a 30 m interval. A 2 m long seine-net of 30.0 m x 2.0 m, with a uniform mesh size of 0.5 cm was used.
Fig. 1. Map of Paraná coast, showing the sampling point in the tidal flat (TF).
SPACH ET AL.: TEMPORAL VARIATION IN FISH ASSEMBLAGES
Simultaneously with the sampling, water temperature, water salinity, and wave height and wave period were measured. Precipitation and wind intensity were obtained from the Centro de Estudos do Mar - UFPR meteorological station in Pontal do Sul. Fish were identified, then weighed (g), and measured (standard and total length in mm) and, when possible, sex and stage of maturity were noted. Data Analysis Samples were grouped by month to analyze temporal variations. A fixed ANOVA model (Sokal & Rohlf, 1995) was applied to examine possible differences between the monthly averages of the physical-chemical parameters and between the monthly averages and those of the groups defined by The Cluster Analysis of the number of species, number of fish, total weight, Margalef’s species richness index, Shannon-Wiener’s diversity index (number and weight) and Pielou’s evenness index (Ludwig & Reynolds, 1988). The data were 4th root transformed and tested for homogeneity of variance (Bartelett’s test) and normality (KolmogorovSmirnov’s test) before applying the ANOVA. The test of the Least Significant Difference (LSD) was used to determine which averages were different if there were significant differences (p
