Seasonal variation of grazing scars on massive Porites corals in Sekisei Lagoon, Okinawa, Japan

Coral reef ecosystems have high biodiversity and unique species interactions. One example is predation on corals by parrotfish species, known for their grazing on surfaces of massive Porites stony corals. However, factors causing variations of grazing scars on Porites colonies remain largely unknown. In this study, we investigated the relationship between ocean depth of Porites colonies, grazing scar ratios, and photosynthetic efficiency, reflecting the health of coral-zooxanthellae symbiosis in Sekisei Lagoon, the largest coral reef in Japan, with distinct seasonality. We documented seasonal variation in photosynthetic efficiency of symbiotic algae and the frequency of grazing scars. Our results suggest that during the cooler season, Porites colonies with higher photosynthetic efficiency may recover from grazing more quickly than colonies with lower photosynthetic efficiency. We also suggest that fish-coral interactions may vary seasonally, possibly in relation to coral reproductive stages and environmental conditions. Further research is needed to understand the complex dynamics of these interactions in coral reefs.