Long-Term Change in Caribbean Reef Water Quality and Ecosystem Health

Caribbean coral reef ecosystems have declined dramatically since systematic monitoring began in the 1970s. Over the past 50 years, they have lost between 50-80% of reef-building corals, their principal ecosystem architects. These declines have been attributed to climate change, introduction of invasive species, overfishing, and land-based pollution. Although recognized as a major stressor to corals, the role of land-based pollution in Caribbean coral declines has not been quantified due to the lack of consistent reef water quality monitoring. As part of our CPN-funded working group “Integrating paleo and historical data into coral reef management and policy”, we compiled several metrics of reef water quality from paleoecological data and disparate monitoring efforts across the Caribbean to document multidecadal-scale change over a period of intensifying coastal land alteration. We then compared water quality trends with trends in living coral cover from these same reefs to assess the role of water quality declines from land-based runoff on coral reef ecosystem health. These analyses show that (1) an array of historical data exist for reconstructing trends in Caribbean reef water quality that are in disparate repositories and remain mostly untapped, (2) reefs across the Caribbean have experienced water quality declines over the past half century, even offshore sites that were previously thought to be unaffected by land-based runoff, (3) correlations between reef water quality and coral abundance trends are detected at select sites where water quality monitoring protocols were consistent and sustained for multiple decades, and (4) water quality declines are asynchronous across sites and are likely related to differing timing and histories of land alteration.