Habitat enhancement for augmenting seawall utilisation by reef fishes in a tropical urban shoreline

Natural habitats in nearshore coastal zones are increasingly being transformed by the addition of coastal defence structures (e.g. breakwaters, seawalls and jetties) that are widely used to protect shorelines and coastal... [ view full abstract ]

Natural habitats in nearshore coastal zones are increasingly being transformed by the addition of coastal defence structures (e.g. breakwaters, seawalls and jetties) that are widely used to protect shorelines and coastal developments from erosion, wave action and sea level rise. These artificial structures typically support lower fish diversity than the natural habitats they have replaced due to limited availability of food and shelter. As seawalls become an increasingly prominent habitat type, understanding how they are utilized by mobile organisms such as reef fishes is important for determining their effect on marine ecosystems. Previous research has shown that abundance and species richness of epilithic organisms on seawalls can be increased by attaching moulded concrete tiles that enhance structural complexity, however, there is limited information on whether these enhancements also affect fish assemblages. In this study, we quantified and compared fish community structure and fish activity (e.g. feeding, taking shelter) between seawall study plots (2.4 m x 2.4 m) with and without habitat enhancement tiles using stationary underwater video cameras during high tides. Video footage revealed that >30 fish species utilize the seawalls, but the families Pomacentridae and Labridae dominated most of the fish assemblage. Increases in foraging activities by some detritivores and invertivores were observed within the enhanced seawall plots, compared to the bare seawall plots. Several fish species, including Choerodon anchorago, Dischistodus fasciatus and some gobiids, used the tiles for shelter. Collectively, these results suggest that eco-engineering habitat enhancements increases the utilization of shallow seawalls by some fish species.