Project: RAPID: Mass Mortality of the Keystone Herbivore Diadema antillarum Underway around the Caribbean Sea

NSF Award Abstract:
The long-spined sea urchin (Diadema antillarum) is an important organism on coral reefs throughout the Caribbean. These urchins feed on algae, thereby helping to keep it from overgrowing the hard corals that form coral reefs. From 1983-1984, a mortality event killed on average 97% of the long-spined urchins and led to a shift in dominance to algae on many coral reefs. That event proceeded rapidly, spreading across the Caribbean in just 13 months and the cause was never identified. A similar event is currently unfolding. This project addresses three interconnected science questions to optimize what can quickly be learned from this temporary event: 1) What urchin population characteristics or environmental conditions may have led to this event and are they like past urchin mortality events around the globe? 2) If a pathogen is responsible for the current mortality event, what is it and can it be transmitted through seawater? 3) Whether the agent responsible for this mortality event is a pathogen, toxin, or something else, how long does it remain viable in seawater, and can oceanographic models be used to explain its distribution and predict its future spread? This event provides a rare opportunity to study a temporary situation in ways not possible after the event is over. Answers to these key questions have broader societal impacts by advancing our knowledge of long-spined urchins, the disease- causing agent; informing local management practices and population monitoring programs; and improving the chance of survival of hatchery-reared animals that will play a critical role in coral reef restoration efforts.

This project addresses three project goals that will optimize what we can learn from this event quickly. First, the investigators are collecting demographic and environmental data from sites that are experiencing mortality and those not yet affected. Second, to optimize diagnostic evaluations and progress toward determination of etiology, histologic assessment of both normal and diseased urchins are being performed. Third, to identify any etiological agent, the investigators are assessing the microbiome and virome of healthy and diseased urchins. Similarly, host transcriptome analyses leading up to gross abnormalities may reveal animal responses to infectious or non-infectious agents. Although a pathogen is suspected, comparative analysis of chemical levels among impacted and non-impacted sites can provide valuable information on contamination levels potentially contributing to stress and immunosuppression in Diadema. The investigators are using tangential flow filtration of mesocosm water to investigate the potential mode(s) of transmission and link to any putative pathogens. They are leveraging existing biophysical models to describe the spread of the disease and contaminants in the wider Caribbean Sea. The models will predict the likely routes and speed that an emergent pathogen and/or contaminant would travel if it remained viable within the water column or travels via shipping lanes.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.