Effects of food sources on the growth, foraging behavior and intestinal microorganisms of sea urchins (Tripneustes gratilla)
Differences in food sources significantly affect the behavior, gut microbiota, and physiology of marine organisms. This study aimed to examine the effects of different algal diets and habitat conditions (presence/absence of coral reef structures) on the growth, gonadal development, digestive enzyme activity, feeding behavior, and gut microbiota of Tripneustes gratilla. Brown algae (Sargassum polycystum, Laminaria japonica) significantly enhanced the body weight and gonadal development, while red algae (Eucheuma gelatinae) promoted gonadal maturation. The presence of coral structures amplified these effects (P < 0.05). Gonad weight was positively correlated with gut weight (P < 0.05). Sea urchins that were fed brown algae showed increased levels of pepsin activity and reduced levels of amylase activity, whereas sea urchins that were fed red and green algae exhibited increased levels of amylase activity. Behaviorally, urchins exhibited diel rhythms and relied more on habitat structures during the day. Foraging and feeding rates were significantly higher in coral reef environments than elsewhere (P < 0.05). Gut microbiota varied by diet, namely, Spirochaetota dominated in the brown algae group, Proteobacteria dominated in the red algae group, and Bacteroidota and Fusobacteriota dominated in the green algae group. The functional predictions revealed enhanced carbohydrate and amino acid metabolism levels in the brown and green algae groups, with notable amino acid metabolism and cell motility levels in the green algae group. The red algae group exhibited functions related to glycan metabolism and antimicrobial resistance.This study demonstrated that algal diet and habitat structure jointly influence the physiological performance, behavior, and gut microecology of T. gratilla, offering theoretical support for optimized aquaculture practices and reef-based ecological management.