Trophic dynamics of three small and short-lived coral reef fishes of the genus Trimma

Abstract Smaller animals may have an enhanced ability to convert microscopic food into biomass, a form of energy that is accessible to larger predators. Small-bodied cryptobenthic reef fishes (CRFs) exploit a variety of small food items and may themselves be important food sources for other coral reef dwellers. However, knowledge regarding the trophic niches of small and abundant CRFs of the genus Trimma is lacking. The aim of this study was to investigate the trophic dynamics of Trimma benjamini , T. capostriatum , and T. yanoi by examining their feeding behaviour, food items consumed, food origins (benthic or pelagic), trophic interactions, and ecological morphology. The majority of individuals (79.7–93.4%) were actively engaged in feeding at a rate of 2.8–3.2 events per minute. These species consumed pelagic items > 99% of the time, where identifiable stomach content revealed a diet consisting mostly of Mollusca larvae (Gastropoda and Bivalvia 32–48.3%) and Copepoda (14.2–28.9%), though there were high amounts of unidentifiable dietary items. The physical attributes of Trimma , such as gape and eye morphology, were well-suited for capturing small and mobile prey. Though complete predation was not observed, 10.2–18.5% of Trimma individuals noticeably avoided some fishes of the Labridae family and experienced a significant decrease in feeding rate of 45.2–80.8% at these times. Interferences by conspecifics or other fish species did not lead to a reduction in feeding rate. Trimma had morphological traits that included cryptic colouration, an elongated body shape, and a reduced caudal fin aspect ratio, which might be beneficial for predator avoidance. This study suggests that Trimma may play ecological roles in importing energy from the pelagic environment and potentially transferring it to predatory organisms.