The decline in the number of sea urchins in the Caribbean may lead to the disappearance of many corals in the region. Florida State University reports.
The sea urchin species Diadema antillarum has long been considered the most important herbivore in the Caribbean, feeding on algae that would otherwise flood the reef and hamper coral growth. However, over the past 40 years, two events have led to a drastic decline in the number of sea urchins. In 1983, an unknown aquatic pathogen wiped out 99% of the species from its entire range in the Caribbean, Gulf of Mexico, and Western Atlantic. Since then, the population has partially recovered, mainly due to shallow water habitats.
A new study off the coast of St. John’s Island (Virgin Islands) has provided a closer look at the population dynamics of hedgehogs. In 2022, the second mass extinction occurred, and now scientists have found that it led to a population decline of 98.00% compared to 2021 and 99.96% compared to 1983. At the same time, in 2021, the area of coral cover was almost an all-time low for the entire period of observations – that is, the coral ecosystem was in a vulnerable position and without a new surge in mortality.
Until 2021, small populations of D. antillarum persisted in shallow water where they grazed and created algae-free zones where coral larvae could attach, establish themselves on the reef and breed. A new surge in mortality has virtually eliminated these populations.
Now, scientists fear, these zones will soon disappear, which will seriously undermine the coral population in the Caribbean.