How climate change and other factors have affected Caribbean reefs for 150 years

A century of warming on Caribbean reefs

Colleen B. Bove, Laura Mudge, and John F. Bruno

Summarized by Habiba Rabiu, a student of environmental geosciences at Fort Hays State University. Habiba is interested in all aspects of environmental science and conservation & sustainability. She would like to work in educating others about those topics. In her free time, she likes to read, write, and bake. 

What data were used? The researchers compiled data from three ocean temperature databases (HadISST, Pathfinder, and OISST) to assess changes in sea surface temperature (SST) and marine heatwave (MHW) occurrences in coral reefs situated in the Caribbean from 1871 to 2020. These data consisted of both in situ readings (those that were taken directly at the surface of the water from boats or buoys) and remote satellite readings. 

Methods: Using data from multiple sources, the researchers determined the locations of 5,326 coral reefs in the Caribbean. Referring to the World Wildlife Fund marine ecoregion classifications, these reefs were sorted into 8 ecoregions. From these data, they assessed the SST for the Caribbean basin as a whole, each ecoregion, and the individual reefs. They also assessed the frequency and duration of MHV events (periods of time, lasting at least five days, when the temperature of a marine area is abnormally high for that location and time) in the basin and the reefs. 

Results: Over the past 150 years, Caribbean coral reefs have warmed by 0.5-1˚C. As a whole, the Caribbean basin has experienced an increase of temperature at a rate of 0.04˚C per decade since 1871 and 0.17˚C per decade since 1981. The rate of increase in each ecoregion differed slightly, with the most recent measurements describing a range from an increase of 0.17˚C per decade in the Bahamian ecoregion to 0.26˚C per decade in the Southern and Eastern Caribbean ecoregions. 

 The frequency and duration of MHW have also increased, particularly since 2010. In the 1980s, MHW occurred once a year on average, which increased to an average of five times a year in the 2010s. This has drastically decreased the return time of the MHW events (the number of days between each event.) In the 1980s an average of 377 days elapsed between each MHW, while in the 2010s, an average of 111 days of return time was recorded. Additionally, recent MHW events have lasted for an average of 14 days compared to the 1980s when they typically lasted less than 10.

The figure shows a series of colored stripes, each of which represents one year from 1870 (on the left) to 2020. The higher temperatures are shown in dark red, which lighten to lighter red and pink as the temperature decreases. The coldest temperatures are shown in dark blue, lightening to paler blues as they get warmer. The left side of the figure (about 2/5 of it) shows mostly blue stripes, while the remainder is mostly pink and red, with the darkest red stripes on the rightmost side showing the late 2010s and 2020.
Stripe diagram showing the increase in mean annual temperature of Caribbean coral reefs, with warmer temperatures (max annual SST of 28.0) depicted in shades of red and cooler temperatures (min annual SST of 26.6) depicted in blue.

Why is this study important? Oceans make up the majority of the Earth’s surface, and the organisms that live there are being greatly affected by global warming and other degradational occurrences in the environment such as sewage pollution and pesticide runoff. Coral reefs are especially rich in biodiversity and contribute greatly to the overall health of the oceans. Given that most marine animals species are ectothermic (they have little to no internal/physiological control of heat and rely on their environment to regulate their temperature), drastic changes in temperature can affect their metabolism, alter their growth rates and caloric needs, cause disease outbreaks, and in some cases lead to the loss of a species entirely which further disrupts the food webs and other delicate systems of the ecosystem. 

The big picture: There are several factors that are causing the destruction of coral reefs, including overfishing (and other human activities), pollution, and overabundance of macroalgae (which thrives in warmer waters), but marine temperature increase has proven to be a primary factor, mainly due to how it causes coral bleaching (when algae is forcibly expelled from the coral, leaving it vulnerable). This is important because it shows that coral reefs are not only affected by regional and local activity, but also by global warming that is largely caused by the activity of first world countries, even if they are not necessarily close to the areas being affected. Halting the ruin of the reefs and other complex ecosystems will require global attention and effort, particularly from more populous, technologically advanced regions that use the greenhouse gasses that are increasing the temperature of the Earth’s surface.

Citation: Bove CB, Mudge L, Bruno JF (2022) A century of warming on Caribbean reefs. PLOS Climate 1(3): e0000002.

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