Caribbean corals have been warming for at least a century

Global warming is modifying countless aspects of marine ecosystems, including species compositions and interactions, marine food webs, metabolic rates and growth of species, disease profiles and rates of primary production. The effects of this degradation are particularly noticeable in the tropical reef ecosystems of the Caribbean, where warming has caused mass coral mortality events, extinction of reef-dependent taxa and the loss of ecosystem function over the past few decades. 

Building on previous research, Colleen Bove of the University of North Carolina at Chapel Hill, and colleagues, present the results of a new analysis of 150 years of sea-surface temperature changes throughout the Greater Caribbean region. Their results, published today in the open-access journal PLOS Climate, provide a synthesis of ocean warming that will help scientists understand how temperatures are impacting these iconic ecosystems.

Initially, the researchers compiled a data base of the locations of Caribbean coral reefs, using the coordinates of known reefs listed in several international sources. In total, they identified the locations of 5,326 unique reefs across the Caribbean Basin. They allocated all the reefs into one of eight ecoregions that they identified using the World Wildlife Fund’s marine ecoregions classification.

They then used three open-access datasets of satellite and on-location sea-surface temperature observations to assess the changes in temperature in the region between 1871 and 2020.

Their analysis showed that, in the Greater Caribbean area as a whole, reef warming began in 1915, although in four of the eight ecoregions, warming began even earlier, during the second half of the nineteenth century. Following a global pause in warming in the mid-twentieth century, warming of the Caribbean reefs resumed in the 1980s and 1990s and has continued ever since then.

The researchers found that Caribbean reefs have been heating up at remarkable rates over the last century: they have warmed by an average of 0.18^oC per decade, during this period, giving a total increase of 0.5 to 1°C in the past century. Different ecoregions have experienced varying rates of warming over time. If the warming trend continues as it has, the authors predict that the Caribbean reefs will warm by an additional1.5°C by the year 2100.

Analysis of the sea-surface temperature data also showed that marine heatwave events have increased in frequency and duration since the 1980s. The Caribbean reefs now experience an average of five heatwave events each year, compared to only one per year in the early 1980s. Recently, these extreme heating events have lasted an average of 14 days. 

“Our study indicates that coral reefs have been warming for at least a century and many reefs across the Caribbean have already warmed by a degree Celsius,” wrote the study authors. “This explains why we have seen such devastating declines in the health of this invaluable ecosystem.”

The experts conclude that the changes in thermal environment, in addition to other stressors such as fishing, pollution and diseases of corals, have caused a dramatic shift in the functioning of Caribbean coral reef ecosystems. They are calling for an urgent reduction in greenhouse gas emissions, as well as plans to address these other stressors, in order to protect the remnant Caribbean coral reefs.

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By Alison Bosman, Earth.com Staff Writer