Turtle Herbivory Suppresses Seagrass Function but Reveals Recovery Potential in a Remote Coral Reef Atoll
5 affiliations
- 1Centre for Marine Ecosystems Research, School of Science Edith Cowan University Joondalup Western Australia Australia
- 2Centre for People Place and Planet Edith Cowan University Joondalup Western Australia Australia
- 3Cocos Marine Care Incorporated Home Island Cocos (Keeling) Islands
- 4Sea Country Solutions Pty Ltd Margaret River Western Australia Australia
- 5Shire of Cocos (Keeling) Islands Home Island Cocos (Keeling) Islands
Abstract
Seagrasses are recognised as ecologically and culturally significant habitats across the globe supporting human livelihoods, biodiversity, and carbon storage. In the Cocos (Keeling) Islands, a remote coral reef atoll in the eastern Indian Ocean, seagrasses provide ecosystem services and support culturally, ecologically, and economically important species. However, these meadows have suffered devastating declines, with ongoing green turtle herbivory identified as a key pressure restricting Thalassia hemprichii persistence.
To examine how herbivory shapes seagrass traits and function, we compared plots protected from grazing for over two years using exclusion cages against continuously grazed plots across two sites.
Seagrass traits at the meadow‐scale (shoot density, leaf area and biomass), as well as some functionality (primary production and nutrient storage capacity), were improved with protection from herbivory pressure. Substantial reductions in the belowground biomass in the grazed plots indicate that these seagrasses are operating under severe metabolic constraints. In contrast, some plant‐scale traits (photosynthetic rate and growth rate) were not altered despite ongoing herbivory pressure, indicating some capacity for recovery at the individual plant scale.
Representing one of the longest turtle exclusion studies in seagrass ecosystems, these results demonstrate that herbivory is driving systemic degradation across multiple biological scales, but these seagrasses currently retain the capacity to recover once grazing pressure is reduced.
Synthesis . Tropical seagrass meadows subjected to continuous herbivory pressure can persist in a chronically depleted state. Herbivore exclusion experiments demonstrate that reducing herbivory can unlock the recovery potential of seagrass. These findings highlight the need for nuanced management strategies to safeguard these meadows in a time where seagrasses continue to decline at both localised and global scales, and the global turtle populations are simultaneously on the rise.
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BibTeX
@article{odea2026turtle,
title = {{Turtle Herbivory Suppresses Seagrass Function but Reveals Recovery Potential in a Remote Coral Reef Atoll}},
author = {Caitlyn O'Dea and Kathryn McMahon and Osman Macrae and Shakirin Keegan and Sahira Bell},
journal = {Ecology and Evolution},
year = {2026},
month = oct,
doi = {10.1002/ece3.74466},
url = {https://onlinelibrary.wiley.com/doi/10.1002/ece3.74466},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Turtle Herbivory Suppresses Seagrass Function but Reveals Recovery Potential in a Remote Coral Reef Atoll
AU - Caitlyn O'Dea
AU - Kathryn McMahon
AU - Osman Macrae
AU - Shakirin Keegan
AU - Sahira Bell
PY - 2026
DA - 2026/10/24
JO - Ecology and Evolution
DO - 10.1002/ece3.74466
UR - https://onlinelibrary.wiley.com/doi/10.1002/ece3.74466
AB - Seagrasses are recognised as ecologically and culturally significant habitats across the globe supporting human livelihoods, biodiversity, and carbon storage. In the Cocos (Keeling) Islands, a remote coral reef atoll in the eastern Indian Ocean, seagrasses provide ecosystem services and support culturally, ecologically, and economically important species. However, these meadows have suffered devastating declines, with ongoing green turtle herbivory identified as a key pressure restricting Thalassia hemprichii persistence. To examine how herbivory shapes seagrass traits and function, we compared plots protected from grazing for over two years using exclusion cages against continuously grazed plots across two sites. Seagrass traits at the meadow‐scale (shoot density, leaf area and biomass), as well as some functionality (primary production and nutrient storage capacity), were improved with protection from herbivory pressure. Substantial reductions in the belowground biomass in the grazed plots indicate that these seagrasses are operating under severe metabolic constraints. In contrast, some plant‐scale traits (photosynthetic rate and growth rate) were not altered despite ongoing herbivory pressure, indicating some capacity for recovery at the individual plant scale. Representing one of the longest turtle exclusion studies in seagrass ecosystems, these results demonstrate that herbivory is driving systemic degradation across multiple biological scales, but these seagrasses currently retain the capacity to recover once grazing pressure is reduced. Synthesis . Tropical seagrass meadows subjected to continuous herbivory pressure can persist in a chronically depleted state. Herbivore exclusion experiments demonstrate that reducing herbivory can unlock the recovery potential of seagrass. These findings highlight the need for nuanced management strategies to safeguard these meadows in a time where seagrasses continue to decline at both localised and global scales, and the global turtle populations are simultaneously on the rise.
SN - 2045-7758
SN - 2045-7758
ER -