Coral suffered from human activities even before carbon dioxide emissions started acidifying the ocean and warming the climate.
A team of oceanographers found that deforestation and fishing seem to have been causing changes in coral reef ecosystems since the early 1900s in the Caribbean off the coast of Panama.
Clearing of forests on land led to increased rain run-off and allowed more soil and pollutants to be washed out to sea. The change in run-off led to a shift in the species of coral and other creatures in the reefs.
Fishing reduced the number of aquatic herbivores, which allowed fast-growing algae to take over.
Over time, branching coral were overtaken by slower-growing non-branching species. Less branching coral meant fewer hiding places and less habitat for marine animals.
Bivalves, such as oysters and clams, grew smaller as deforestation increased as well. Populations of the two dominant species, staghorn coral and tree oysters, declined drastically.
To develop a timeline of reef changes, the oceanographers dug below modern reefs and used radiocarbon dating to give ages to the coral skeletons and shells they found. They then correlated the changes in reef species to historical records of land clearing.
The research was led by scientists at the Scripps Institution of Oceanography at the University of California, San Diego, and is published in the April issue of Ecology Letters.
Photo: Basalt rocks covered in corals (live and dead), crinoids, sponges, and brittle stars. Credit: NOAA, Wikimedia Commons.