Spatial variability of fish communities in a highly urbanised reef system

Abstract

Rapid coastal development has generated interest in the ecology of human-modified marine environments. Coastal defence structures such as breakwaters and seawalls are increasingly built to reduce erosion and to mitigate the impacts of sea level rise but knowledge on the marine biodiversity around these structures is lacking. Benthic cover and fish community were surveyed at nine offshore sites, comprising seven coral reefs and two seawalls, in the Singapore’s highly urbanised reef system. A total of 4943 fishes from 70 taxa were recorded, dominated by Pomacentridae (56.5%) and Labridae (17.7%). The results showed a clear spatial variation in the fish community structure across the reefs. The southwestern reefs supported fish communities that were significantly different from those in the south. Generic diversity was significantly higher at the southwestern reefs than the southern ones while the abundance and generic richness were similar. The differences in fish community structure were moderately correlated with the abundance of coralline algae, foliose and submassive corals. The seawall sites supported fish communities different from coral reefs that were adjacent to them. While abundance was similar, the former had higher generic richness and diversity than the latter. The difference in community was attributed to two pomacentrid genera (i.e. Neopomacentrus and Pomacentrus) which were more abundant at the reefs. The findings demonstrated that urbanised coastal ecosystems can contribute to supporting fish diversity.