Seasonality in fish assemblage structure in an East African mangrove creek

Abstract

The spatial and seasonal structures of fish assemblages in a tropical mangrove tidal creek, Tudor, Kenya, were analysed from monthly survey data, extending from October 2007 to July 2008, and covering the north-east (NEM; October–March) and south-east (SEM; April–July) monsoon seasons. A total of 2 118 individuals, representing 84 species belonging to 49 families, were caught. Gerres oyena, Terapon jarbua and Lutjanus fulviflamma were the dominant species in all seasons. There was within-creek seasonal variability in species abundance and diversity. Overall, the mean density (individuals m^–2) was higher during the SEM season (0.368; SE 0.078) than the NEM season (0.255; SE 0.041). The NEM season had significantly more species (n 69) than the SEM season (n 63) (χ² = 317.891, p < 0.0001). Two-way ANOVA indicated the influence of season and habitat on abundance of some species. The abundance of creek-resident species was significantly influenced by site whereas abundance of creekdependent and transient species was influenced by interaction between seasons and stations. Bray-Curtis cluster analysis defined two species assemblages, reflecting differences in temporal and spatial use of the creek by the fish species. Correspondence analysis indicated that seasonal fish assemblages were only distinct at the mouth of the creek with less clear seasonal structure in the upper region of the creek.