The migration of an expanding sea turtle population alters the structure of marine megafauna communities

Abstract

Interactions shape community structures, yet the impact of large migratory influxes on communities, particularly marine ones, remains elusive. Using drone surveys, we investigated changes of marine megafauna communities (e.g., sharks, rays), during the mass migration of loggerhead sea turtles (Caretta caretta) in Cabo Verde, one of the largest, and growing, rookeries globally and a biodiversity hotspot. In high nesting density areas, with over 6,000 turtles detected in-water at the seasons peak, the community structured with sharks distributing between the turtles and the coastline. In low-density areas ([~]500 turtles), no structuring was detected. After the seasons peak, increased shark abundance and shoreward movement suggest they anticipate a nutrient pulse from emerging hatchlings. Our results highlight the role of sea turtle abundance in structuring marine communities, both as a high-quality food resource (hatchlings) and a likely non-consumable species (adults). Overall, we show the significant impact of migratory species on marine megafauna communities.