Seasonal and diel changes in a subtropical mangrove fish assemblage

Abstract

Fish were sampled by fyke nets for a year over diel cycles and a seasonal cycle in a subtropical mangrove creek of northern Taiwan. A total of 30 fish species belonging to 18 families were captured; Gobiidae and Mugilidae were the most diverse families. The fish assemblage was dominated by a small number of small-sized and commercially important species. Total fish number and biomass were highly variable and showed little seasonal differences. However, species richness and diversity were significantly higher in fall than in winter-spring. An ordination analysis demonstrated that monthly changes in species composition followed a gradual pattern and showed a clear seasonal cycle. A combination of water temperature and salinity best explained the monthly changes in species composition. Pearson correlations indicated that water temperature was positively correlated, and salinity was negatively correlated, with the species richness and diversity. There were no significant diel differences in total fish number and species richness. However, biomass and diversity were significantly higher at night than during the day. Classification and ordination analyses showed that there were distinct 'day' and 'night' assemblages in winter-spring and fall, but not in summer. Our results suggest that a seasonal cycle was more important than diel cycles in structuring temporal changes in the fish assemblage of a subtropical mangrove creek.