Resource partitioning among algal turf-feeding fishes on a tropical artificial shoreline.

Rapid coastal development has led to the proliferation of artificial structures along urban shorelines. Numerous studies have shown that patterns of fish diversity associated with these novel habitats are driven by physical habitat complexity; however, trophic-mediated processes in shaping these patterns remain poorly understood. Foraging behaviour and resource partitioning are key strategies that explain habitat use and co-occurrence of ecologically similar species. In tropical artificial shorelines, algal turfs dominate the benthic assemblages and provide a variety of dietary sources (e.g., algae, detritus, microbes, small invertebrates) for multiple trophic groups of fishes. Using carbon and nitrogen stable isotopes, we investigated the trophic niches of 13 common algal turf-feeding fish species on a granite rip-rap seawall in Singapore. We first compared diet compositions among these species by using hierarchical Bayesian mixing models, incorporating prior diet data from gut content and the literature. We then computed ellipse areas based on carbon and nitrogen isotope signatures to compare isotopic niche size as well as 'typical' (40% of data) and 'total' (95% of data) niche overlaps among these species. Our results revealed varying diet compositions and trophic niche sizes among species, while clear separations in 'typical' niche despite significant overlaps in 'total' niche among some species indicate resource partitioning. Our findings underscore the role of trophic-mediated mechanisms in shaping seawall fish assemblage patterns and the importance of algal turfs as vital food resources that facilitate fish species co-occurrence.