Beyond predators: medusae as the link between the classic pelagic food web and the microbial food web

• Grant number: 24/22055-6
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: October 01, 2025
• End date: September 30, 2028
• Field of knowledge: Biological Sciences - Ecology - Ecosystems Ecology
• Principal Investigator: Camila Negrão Signori
• Grantee: Mayara de Almeida Jordano
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Medusae are polytrophic predators capable of surviving in oligotrophic environments. However, the mechanisms underlying their survival and proliferation in such environments remain a major knowledge gap. Based on physiological and ecological evidence presented here, we hypothesize that medusae can also absorb dissolved organic matter (DOM) and capture bacteria, thereby linking the microbial food web in oligotrophic environments to the classical food web (i.e., "macrobial loop"), making carbon available to higher trophic levels. To test this, ephyrae and medusae of Aurelia coerulea and Lychnorhiza lucerna will be subjected to experimental diets (i.e., no food source, only Artemia sp. nauplii, DOM collected and obtained from phytoplankton excreta, Artemia sp. nauplii + DOM, and bacteria) to assess their organic production. Results will be compared to the stable isotope composition of medusae collected from the wild to evaluate the correspondence between laboratory treatments and their estimated ecological roles. Isotopic niche analysis and trophic level estimation will allow the evaluation of the relative importance of potential food sources through a complementary approach to the organic production experiments. Additionally, we aim to quantify DOM absorption and its impact on the carbon cycle by measuring ingestion rates. Finally, we will test for possible differences in organic production contributions related to bacterial and DOM ingestion between the ephyra and medusa stages. This project will investigate an unknown trophic pathway that could reshape our understanding of the role of jellyfish in global carbon fluxes and marine biogeochemistry. (AU)