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Title

Sequential overgrazing by green turtles causes archipelago-wide functional extinctions of seagrass meadows

AuthorsGangal, Mayuresh; Gafoor, Al-Badush; D'Souza, Elrika; Kelkar, Nachiket; Karkarey, Rucha; Marbà, Núria CSIC ORCID ; Arthur, Rohan CSIC ORCID ; Alcoverro, Teresa CSIC ORCID
KeywordsMega-herbivores
Foraging aggregations
Overgrazing
Habitat loss
Phase shift
Issue Date2021
PublisherElsevier
CitationBiological Conservation 260 : 109195 (2021)
AbstractAfter centuries of decline, green turtle (Chelonia mydas) populations are showing handsome localized recoveries due to dedicated conservation efforts. This calls into question how much herbivory can be sustained by seagrass meadows that these turtle populations feed on. In our study, we documented the long-term impacts of green turtle foraging on seagrass meadows in the Lakshadweep archipelago, Indian Ocean. We tracked green turtle densities and seagrass areal extent in five atolls across the archipelago since 2005. Turtle densities first grew to record levels in the seagrass meadow of the Agatti lagoon around 15 years ago. Within a few years of intense herbivory, the meadow underwent radical biomass reduction and compositional shifts, leading to functional extinction and ultimately, bare sand. This trajectory of decline wtas repeated in every atoll, with turtle aggregations persisting 2 to 6 years before meadows were depleted, depending on their initial size. By 2019, all large meadows had declined, and in 2020, green turtles were distributed at low densities in every meadow. The meadows were limited to small patches of early successional species, maintained in a state of protracted recovery by constant, low-level herbivory. We measured the impacts of turtles on two key ecosystem services, a habitat for fish communities and stored organic carbon. Turtle overgrazing resulted in massive declines in seagrass fish diversity, biomass, and abundance, and major reductions in sediment-stored carbon. Apart from being important conservation flagships, green turtles are strong ecosystem interactors, and can potentially cause trophic cascades or functional extinction of seagrass ecosystems.
DescriptionEste artículo contiene 10 páginas, 5 figuras, 1 tabla.
Publisher version (URL)https://doi.org/10.1016/j.biocon.2021.109195
URIhttp://hdl.handle.net/10261/243085
ISSN0006-3207
Appears in Collections:(CEAB) Artículos
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