Ecological importance of sea turtles in coastal marine ecosystems

Sea turtles have experienced dramatic declines over the past century. However, in some cases, populations have recovered from past exploitation.

Sea turtles play important roles in a variety of marine ecosystems through grazing, nutrient recycling and translocation, foraging facilitation, and ecosystem engineering.

Species

Green turtle (Chelonia mydas), hawksbill turtle (Eretmochelys imbricata)

Nosy Be Island
French West Indies

This species is currently classified as ‘Critically Endangered’ in the IUCN Red List of Threatened species, and their populations seem to be declining globally due to poaching (for shell trade), bycatch in gillnets, and habitat destruction.

Through different projects, we study how sea turtles affect ecosystem dynamics in the Caribbean Sea and Madagascar

In coral reef ecosystems, we study the roles and importance of hawksbill turtles (Eretmochelys imbricata) along the coasts of northwestern Madagascar. Hawksbill turtles are omnivorous consumers occurring in coral reef ecosystems. This species is currently classified as ‘Critically Endangered’ in the IUCN Red List of Threatened species, and their populations seem to be declining globally due to poaching (for shell trade), bycatch in gillnets, and habitat destruction. Their ecology and behavior is poorly understood, particularly on their foraging grounds. They can promote the growth of hard corals through predation on sponges, thus, their removal could significantly affect the structure and function of coral reef ecosystems. However, the ecological roles and importance of hawksbill turtles in coral reef ecosystems has not been investigated in detail, and the identification of foraging grounds for hawksbill turtles is still poorly understood in many regions, including in the western Indian Ocean and in Madagascar. We study the abundance, distribution and ecology of hawksbill turtles in the Nosy Be Island region using multiple methods, including tow-diver surveys, focal follow sampling, and animal-video deployments to better understand how coral reef habitats affect this species. We also study how hawksbill turtles influence sponge and algae growth on reefs, and how they could possibly influence the structure and resilience of coral reef ecosystems.

Since 2016, we have studied how green turtle habitat use and foraging decisions have been impacted by invasive seagrass and other ecological pressures acting synergically (e.g. hurricanes, disturbance from tourism) in the southern Caribbean, particularly in the French West Indies.

In seagrass habitats (Caribbean and Indo-Pacific), we study the fine-scale distribution and abundance of green turtles (Chelonia mydas), and how this species can be affected by seagrass degradation. Green turtles are endangered on a global scale, but due to focused conservation and management efforts, some regional populations are increasing. As grazers, green turtles act as ecosystem engineers, and their grazing behavior has the potential to affect competition between foraged species including between native and non-native species. Halophila stipulacea, a fast growing, highly tolerant, seagrass native to the Indian Ocean, has achieved transoceanic establishment in the southern Caribbean. Understanding the factors that influence foraging distributions, food selection, and ecological impacts of green turtle populations may be particularly critical in areas where there are bottom-up disruptions to ecosystems like the presence of invasive species. Since 2016, we have studied how green turtle habitat use and foraging decisions have been impacted by invasive seagrass and other ecological pressures acting synergically (e.g. hurricanes, disturbance from tourism) in the southern Caribbean, particularly in the French West Indies. In seagrass beds of northwestern Madagascar, we study how green turtle foraging is affected by a variety of natural and anthropogenic pressures, including food availability and human induced disturbance from coastal fisheries and tourism.