Restoration of a herbivore to save Caribbean coral reefs

The 1980s saw the mass die-off of the long-spined sea urchin Diadema antillarum, one of the Caribbean’s most important coral reef herbivores. For a long time, scientists were puzzled by the widespread, damaging and enduring impact this event had on Caribbean reefs. The recent discovery of the region’s last remaining healthy population enabled Wallacea Trust scientists to link the poor recovery to the reduction of reef structural complexity caused by the initial loss of the urchins. We are now working with local stakeholders to deploy artificial reefs and re-introduce urchins at sites across the Caribbean.

"When it comes to Diadema, we can tell people a better story, a story that has a better ending. If we re-introduce Diadema there is a possibility that we could save our reefs"

The long-spined sea urchin, Diadema antillarum, has an insatiable appetite for macroalgae. A coral reef without corals is comparable to a forest without trees, and these urchins spend their nights removing macroalgae from Caribbean reefs, clearing space for corals to dominate and keeping the ecosystem healthy. For millennia, Caribbean coral reefs have been maintained by the presence of these urchins, until a disease in the early 1980s wiped out over 95% of their total population. This led to an explosion of macroalgae, and subsequent catastrophic declines in Caribbean reef health.

In the 30+ years since mass mortality, population recovery has largely failed, and Caribbean coral reefs continue to deteriorate. However, the newly discovered reef system of Banco Capiro in Tela Bay, Honduras, offers a glimmer of hope among the doom and gloom. Urchin densities are high enough to support one of the healthiest reefs found anywhere in the Caribbean today.

Wallacea Trust scientists have been studying Banco Capiro since 2013, attempting to discover what has allowed such a uniquely healthy population of urchins to exist today, and thus what has prevented recovery throughout the rest of the Caribbean. Their findings suggest that 3D complexity could be the answer. Urchin loss led to coral loss, and this in turn drastically reduced the structure of the reef, making it harder for urchins to hide from predators. They are now conducting experiments using artificial reefs combined with Diadema re-introductions on degraded reefs, and preliminary results have shown an increase in urchin populations, a decrease in macroalgae, and an increase in coral; signs that a successful conservation answer could be right around the corner.

Next, the Wallacea Trust aims to engage local and regional stakeholders to deploy artificial reefs at sites across the Caribbean, ultimately creating new business opportunities for local communities through dive eco-tourism.

University of South Wales PhD student Natalie Lubbock collects urchins on the reefs around Utila island to better understand the ecology and physiology of "suppressed" populations.
Open University PhD student Max Bodmer constructs the first set of artificial reefs to test their use in restoring urchin populations - by using cheap and locally available materials, the feasibility of expanding the project is maximised.
University College Dublin student Sanni Hintikka takes genetic samples from urchins in the Tela Marine Research Centre's aquarium facility.
Having identified a lack of 3D complexity as a primary barrier to urchin recovery, our team of scientists are now exploring how artificial refuges might be used to increase urchin survival.
The urchin research team embark on a dawn dive to the reefs of Banco Capiro in Tela Bay, Honduras.
By collecting urchins from different reef systems, tissue samples can be taken and exported to the UK genetic differences between each population can be investigated.
Juvenile urchins could hold the key to restoring their populations, as evidence suggest there is a bottleneck preventing enough individuals from reaching maturity.