Increasing ocean temperature reduces primary productivity in three Caribbean seagrass species: implications for future ecosystem function

Seagrass meadows are composed of key marine foundation species that support coastal ecosystems through habitat provision and high primary productivity. Yet, since photosynthetic performance peaks at species-specific optimal temperatures, rising ocean temperatures may increasingly exceed these limits, reducing seagrass cover and impairing ecosystem function. To evaluate the effects of warming on productivity, we quantified the thermal sensitivity of gross primary production (GPP) and respiration in three Caribbean seagrass species: Thalassia testudinum , Syringodium filiforme , and Halodule wrightii. Seagrass blades were exposed to nine environmentally relevant temperatures, and oxygen fluxes were measured in respirometry chambers under standardized light and dark conditions. Modeled thermal performance curves (TPCs) revealed peak GPP at an optimal temperature ( T opt ) of ∼31 °C, with H. wrightii showing the highest maximum photosynthetic rate ( P max = 2.0 log μmol O 2 g −1 h −1 ), followed by T. testudinum (1.8 log μmol O 2 g −1 h −1 ) and S. filiforme (1.7 log μmol O 2 g −1 h −1 ). Above 32 °C, GPP declined sharply across species, indicating reduced photosynthetic performance. These results suggest that continued ocean warming may significantly impair the productivity and ecological function of Caribbean seagrasses, with broad implications for coastal marine ecosystems.