Seagrass coastal protection services reduced by invasive species expansion and megaherbivore grazing

1. Seagrasses provide an important ecosystem service by creating a stable erosion-resistant seabed that contributes to effective coastal protection. Variable morphologies and life history strategies, however, are likely to impact the sediment stabilisation capacity of different seagrass species. We question how opportunistic invasive species and increasing grazing by megaherbivores may alter sediment stabilisation services provided by established seagrass meadows, using the Caribbean as a case study.

2. Utilising two portable field-flumes that simulate unidirectional and oscillatory flow regimes, we compared the sediment stabilisation capacity of natural seagrass meadows in situ under current- and wave-dominated regimes. Monospecific patches of a native (Thalassia testudinum) and an invasive (Halophila stipulacea) seagrass species were compared, along with the effect of three levels of megaherbivore grazing on T. testudinum: ungrazed, lightly-grazed and intensively-grazed.

3. For ...