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Looking for the sponge loop: analyses of detritus on a Caribbean forereef using stable isotope and eDNA metabarcoding
Lauren K Olinger1,2, Beverly McClenaghan3, Mehrdad Hajibabaei3,4
1Center for Marine and Environmental Studies, University of the Virgin Islands, St Thomas, Virgin Islands, U.S. Virgin Islands, United States of America.
Peerj
|February 27, 2024
Summary
Coral reef detritus is primarily from algae and other organisms, not sponges as hypothesized. This study found sponges contribute minimally to reef detritus, challenging the sponge loop hypothesis.
Area of Science:
- Marine biology
- Ecology
- Biogeochemistry
Background:
- Coral reefs depend on detrital pathways for nutrient cycling.
- The sponge loop hypothesis suggests sponges are key consumers of dissolved organic carbon (DOC) and significant detritus producers.
Purpose of the Study:
- To investigate the sources of detritus in the epilithic algal matrix (EAM) on a Caribbean coral reef.
- To test the validity of the sponge loop hypothesis by assessing sponge contribution to reef detritus.
Main Methods:
- Sampling of EAM detritus and potential detritus sources over two seasons.
- Stable isotope analyses to trace organic matter sources.
- eDNA metabarcoding to identify the taxonomic composition of detritus.
Main Results:
- EAM detritus primarily originated from micro- and macroalgae (primary producers).
- Metazoans, including sponges, were minor contributors to EAM detritus.
- Sponge species implicated in detritus production were not detected in EAM samples.
- Detritus composition varied seasonally, with mixed pelagic/benthic sources in summer and primarily benthic in spring.
Conclusions:
- The sponge loop hypothesis is not supported by the findings, as sponges contribute negligibly to reef detritus.
- Detritus on this coral reef is a complex mixture of benthic and pelagic inputs, with primary producers being dominant.
- Seasonal environmental conditions influence the sources of detritus in the epilithic algal matrix.
