Characterization of gelatinous plankton component in the diet of Dermochelys coriacea and Chelonia mydas (Testudines)

• Grant number: 23/06962-0
• Support Opportunities: Scholarships in Brazil - Master
• Start date: January 01, 2024
• End date: February 28, 2025
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Biological Oceanography
• Principal Investigator: Aurea Maria Ciotti
• Grantee: Débora Melo Mendonça
• Host Institution: Centro de Biologia Marinha (CEBIMAR). Universidade de São Paulo (USP). São Sebastião , SP, Brazil

Abstract

Sea turtles are migratory animals, using different areas during their life cycle to fulfill vital functions such as feeding and reproduction. However, changes in meteo-oceanographic variables in a particular region can also interfere in their feeding habits, as they alter the distribution of important food components, such as gelatinous plankton, known to be present in the diets of leatherback and green turtles. However, correct identification of gelatinous plankton as a food item requires specific techniques, because its tissues characteristically have rapid digestibility, and the quantification of its presence in the feeding ecology of sea turtles is still precarious. In this context, our study will investigate the role of gelatinous plankton in the diet of sea turtles of the species Dermochelys coriacea and Chelonia mydas on the southern coast of São Paulo State, based on samples obtained in daily beach monitoring in Cananéia, Ilha Comprida and Iguape, performed between 2019 and 2023. Food items will be screened for gelatinous plankton individualization, identifying under stereomicroscope diagnostic features such as nematocysts. The data will be used to estimate an index of relative importance of gelatinous plankton in the diet of these species. These data will be crossed with sea turtle stranding occurrences, search of seasonal patterns or relationship with the trophic state of the environment, being estimated by sea surface temperature and chlorophyll concentration data obtained by remote sensing, and potential relationships with dates of cold front passages. We tested the hypothesis that leatherback and green turtles prey on gelatinous plankton in the region of interest, this component being underestimated so far in the diet of these organisms by methodological artifacts.