Tidal variation in fish assemblages and trophic structures in tropical Indo-Pacific seagrass beds

Chen-Lu Lee,Hsing-Juh Lin,Yen-Hsun Huang,Chia-Yun Chung

doi:10.1186/s40555-014-0056-9

Chen-Lu Lee, Hsing-Juh Lin + Show 2 more

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https://doi.org/10.1186/s40555-014-0056-9

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Abstract

Abstract Background Tidal cycle is an important factor which regularly changes coastal fish assemblages in shallow waters. However, the variations in fish assemblage and trophic structure across tidal cycles in tropical seagrass beds are rarely discussed. We used underwater visual censuses to quantify fish abundance and diversity from the shallow intertidal to the subtidal zone during both flood and ebb tides in seagrass beds surrounding the Dongsha Island, South China Sea. We also recorded fish feeding habits by analyzing stomach contents. Results At least 70 fish species were observed in the seagrass beds during the study periods. Fish density and diversity increased with increasing depths, as well as during flood tides. The intertidal areas were characterized by more variation in both fish assemblage and trophic structure than the subtidal areas. A cluster analysis identified six principal feeding groups and invertebrate-feeding carnivores contributed about 70% of the total fish abundance. The density of herbivores, large-sized carnivores, and piscivores, but not small-sized carnivores, increased during flood tides. In contrast, detritivores decreased in density during flood tides. A heatmap of habitat usage pattern revealed that most fish showed a preference for deeper stations and flood tides. Only a minority of fish showed a preference for shallower stations and ebb tides. Conclusions We documented differences in fish assemblage and trophic structure between tides in tropical seagrass beds. Our results suggest that water depth may account for a significant proportion of the variation. The deeper water during flood tides support more space for herbivores and high trophic level carnivores to forage in intertidal meadows. The remaining, non-ebbed seawater columns in the intertidal meadows formed important temporary refuges for fishes during ebb tides. This study offers new information for fish movements over tidal cycles in tropical seagrass beds.

Highlights

Tidal cycle is an important factor which regularly changes coastal fish assemblages in shallow waters
A significant depth difference was found between stations, and N was deeper than the two intertidal stations
There were no significant differences in seagrass cover, density, and biomass among stations (Table 1); the epiphyte biomass at N was higher than at the other stations

Summary

Introduction

Tidal cycle is an important factor which regularly changes coastal fish assemblages in shallow waters. Seagrass beds are known as shelters, nurseries, and foraging grounds for numerous marine animals in coastal regions (e.g., Parrish 1989; Duffy 2006) These ecosystem services connect certain coastal habitats via the movements of various nekton and fish species. During flood tides, the higher water level generally permits more fish from neighboring habitats to enter shallow areas (Robertson and Duke 1990; Krumme 2004). The entrances of these transient fish can lead to an overall increase in fish abundance, and this may alter the trophic structure of the ecosystem on a short-term timescale. The seawater level decline associated with ebb tides may cause many fish to leave the shallow areas to avoid certain environmental constraints, such as increasing temperature or salinity (Ayvazian et al 1992) or the increased risk of predation (Sogard et al 1989)

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