Multi-trophic markers illuminate the understanding of the functioning of a remote, low coral cover Marquesan coral reef food web

Pauline Fey,Daniela Bănaru,Nicholas V C Polunin,Yves Letourneur,Valeriano Parravicini,Tarik Meziane,Mayalen Zubia,Benoit Lebreton,Jan Dierking,René Galzin

doi:10.1038/s41598-021-00348-w

Abstract

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and meso- to eutrophic waters. The Marquesas constitute a relevant ecosystem to understand the functioning of low diversity reefs that are also subject to global change. A multi-tracer assessment of organic matter pathways was run to delineate ecosystem functioning, using analysis of fatty acids, bulk and compound specific stable isotope analysis and stable isotopes mixing models. Macroalgae and phytoplankton were the two major food sources fueling this food web with, however, some marked seasonal variations. Specifically, zooplankton relied on phytoplankton-derived organic matter and herbivorous fishes on macroalgae-derived organic matter to a much higher extent in summer than in winter (~ 75% vs. ~ 15%, and ~ 70 to 75% vs. ~ 5 to 15%, respectively) . Despite remarkably high δ15N values for all trophic compartments, likely due to local dynamics in the nitrogen stock, trophic levels of consumers were similar to those of other coral reef ecosystems. These findings shed light on the functioning of low coral cover systems, which are expected to expand worldwide under global change.

Highlights

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and mesoto eutrophic waters
Fatty acids are used to assess how the various sources of organic matter are integrated by primary consumers and by secondary consumers, AA-CSIA provide information on both the assimilated baseline and the length of food chains, while bulk stable isotope analyses allow to describe the global structure of the food web
Despite the peculiar ecological characteristics of these coral reefs, fatty acid, C and N stable isotope data evidenced that this system maintains a high productivity fueled by phytoplankton and zooplankton, most likely of pelagic origin

Summary

Introduction

We studied the food web structure and functioning of a coral reef ecosystem in the Marquesas Islands, French Polynesia, characterized by low coral cover, high sea surface temperature and mesoto eutrophic waters. Fatty acids are used to assess how the various sources of organic matter are integrated by primary consumers (herbivores) and by secondary consumers, AA-CSIA provide information on both the assimilated baseline and the length of food chains, while bulk stable isotope analyses allow to describe the global structure of the food web. The combination of these methods allowed us to address five major questions: (i) What are the main sources of organic matter that fuel the food web of the Marquesas coral reefs, and (ii) how is this organic matter integrated by primary consumers?

Methods

Discussion

Conclusion