Trophic guild structure and dietary patterns of a juvenile-dominated demersal fish community in a tropical mangrove estuarine system

Abstract

Community-wide understanding of food web dynamics in species-rich tropical estuaries are generally lacking, exacerbating the challenges of managing these valuable coastal habitats. To address this gap, trophic guilds and dietary patterns were elucidated for 39 species of a juvenile-dominated demersal estuarine fish community in the Matang Mangrove Forest Reserve, an Important Marine Mammal Area. Fishes were sampled monthly for a year using otter trawl, and stomach contents were analyzed. Of the seven trophic guilds identified from clustering analysis, the three most speciose ones were shrimp feeders (12 species), zooplanktivores (9), and generalist crustacivores (7). Copepods occurred in diets of 50% of all fish species and were the most important food item volumetrically for specialist zooplanktivores. Diverse shrimp and prawn taxa, including commercially valuable Acetes and juvenile penaeids, showed highest frequency of occurrence in stomachs and supported the shrimp feeder and crustacivore guilds that contained relatively more diet generalists. Biomass-dominant annelidivore guild members are known to be a vital food resource for highly threatened coastal cetaceans. Ontogenetic diet shift, wide intra-guild diet breadth, seasonality in major resource use, and prevalence of detritus in diet were feeding strategies that reduced niche overlap and competition among fish species sharing common food resources. Future fisheries management must consider the bottom-up trophic impacts from excessive removal of valuable prey resources such as shrimps on equally valuable fish consumers that depend on them.