Expansion and fragment settlement of the non-native seagrass Halophila stipulacea in a Caribbean bay

ABSTRACT

The non-native seagrass species Halophila stipulacea has spread throughout the Eastern Caribbean since 2002, and could potentially impact the functioning of local seagrass ecosystems. Important characteristics for invasiveness, such as dispersal, recruitment and expansion of H. stipulacea at a local scale, are unknown. We assessed H. stipulacea expansion rates within Lac Bay, Bonaire, Dutch Caribbean (7 km²), since its establishment in 2010 and tested the settlement potential of uprooted vegetative fragments of H. stipulacea. Using 49 fixed locations, we observed that between 2011 and 2015 the occurrence of H. stipulacea in the bay increased significantly from 6% to 20% while native Thalassia testudinum occurrence decreased significantly from 53% to 33%. Free-floating H. stipulacea fragments that were collected and tethered above the sediment rooted within 10 days with a settlement success rate of 100%. The growth of settled fragments was on average 0.91 shoots d⁻¹. The ongoing shift from native T. testudinum to introduced H. stipulacea dominated meadows may have important consequences for multiple Caribbean seagrass ecosystem functions. Given the large difference in size between the two seagrass species, functions such as coastal protection, habitat structure, food availability, and the stability and resilience of these systems can be altered. The next steps towards modelling future expansion of H. stipulacea throughout the Caribbean and beyond should include the assessment of fragment viability and dispersal distance, and the impacts of natural and anthropogenic disturbance on vegetative fragment density, dispersion and settlement by this species.

RESPONSIBLE EDITOR:

• David Thieltges

KEYWORDS:

• Dutch Caribbean
• ecosystem services
• exotic seagrass
• Halophila stipulacea
• range expansion
• vegetative fragmentation

Acknowledgements

We would like to thank Caren Eckrich (STINAPA) for assisting in the field with the seagrass mapping, and Lisa Becking for suggestions on the research setup and logistic support.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Fee O. H. Smulders http://orcid.org/0000-0003-4124-8355

Additional information

Funding

This work was supported by the Volkert van der Willigen grant 2015 of the Amsterdam University Fund to Fee Smulders and NWO (Nederlandse Organisatie voor Wetenschappelijk Onderzoek) grant no. 858.14092 to Marjolijn Christianen.