Sea Urchin Studies And Ecosystem Restoration
In the last few decades, the long-spined sea urchin (Diadema Anthillarum) suffered two massive die-offs that wiped out 97% of populations across the Caribbean. Today, only 20% of the population is estimated to have recovered, leaving most reefs with low numbers of this ecologically significant species. Because Diadema are key grazers that keep algae under control, their decline has contributed to a phase-shift allowing coral-dominated reefs to become overgrown with algae. Near-shore reefs in St. Kitts and Nevis are particularly affected by this macroalgae overgrowth, threatening reef health and the species that depend on it
To better understand how sea urchin populations are recovering, we are studying Diadema recruitment rates along St. Kitts nearshore reefs. Sea urchin start their life cycle as larvae, that float in the water column for 36-60 days, until they find a suitable substrate where to settle.
Researchers have proposed that this initial phase could be the ‘bottle-neck’ causing their slow recovery. In 2024 we conducted our first survey and looked for the presence of juvenile settlers, a stage in which Diadema are only about 1-5mm in size. After monitoring for 6 months, we could not find any settlers on the collectors, which could be a result of more factors such as location, high mortality or low larval supply.
Our efforts will continue in order to further study how Diadema populations are recovering in St Kitts waters. Restoring grazers is only one part of our ecosystem-based approach. We must first look at the reef ecosystem holistically if we want to improve health, biodiversity and the services it provides, while adapting to a changing climate.
This project is in collaboration with Alwin Hylkema, researcher and expert from Saba, Dutch Caribbean and Kenneth Dive Center, St. Kitts.