Interlinkage between Caribbean coral reefs and seagrass beds through feeding migrations by grunts (Haemulidae) depends on habitat accessibility

Abstract

Tropical marine habitats are often energetically linked through feeding migrations by fish. A widely accepted assumption is that species of Haemulidae (grunts) undertake nocturnal feeding migrations from coral reefs to seagrass beds. This has been based on studies investigating migrations between small patch reefs and surrounding seagrass beds located in lagoons. Due to the size and location of these patch reefs, we argue that this does not represent migration from coral reef to seagrass ecosystems, and a literature search shows limited proof for such migration. We hypothesised that the spatial arrangement of these habitats in the seascape may have profound effects on the degree to which such migrations occur. Haemulon flavolineatum caught from seagrass beds located in semi-enclosed embayments, and thus isolated to a high degree from adjacent reefs, showed a diet and stable isotope signature of muscle tissue that differed from those collected from the coral reef. In contrast, fishes from open seagrass systems without restricted access from the reef showed the same stable isotope signature as those collected from the coral reef, suggesting feeding from the same habitat, viz. the seagrass beds. Additional visual census data showed that semi-enclosed seagrass beds did not have elevated densities of large-sized fish at night, which would be expected if large individuals from the reef migrated to the seagrass beds to feed. The data thus show that interlinkages between coastal ecosystems, such as coral reefs and seagrass beds, by fishes may strongly depend on the spatial arrangement of habitats within the seascape.