Diadema urchin mass mortality

In late March, Ian (along with several other microbiologists) was contacted by several scientists and resource managers in the Caribbean who were seeing a new mass mortality in Diadema antillarum (the long-spined black urchin). This species plays a very significant role in mediating the balance between macro algae and corals in Caribbean reef ecosystems – both compete for space and it is largely through Diadema’s grazing on macro algae that coral succeeds in these environments. Diadema, which were once very numerous throughout the region, suffered an enormous mass mortality in the early 1980s (see the many amazing papers by Haris Lessios documenting the decline). That event started on the Atlantic side of the Panama Canal, moving eastwards along the north coast of South America and northwards along Belize and Quintana Roo (Mexico) before demolishing populations in the windward islands, the Antilles, and finally the coral reefs of Florida. Ultimately the loss of these important herbivores caused an ecosystem shift, considerably damaging coral extent. The cause of the early 1980s event remains unknown, though it was widely believed to be caused by some kind of infectious agent.


Just like in the early 1980s, the cause of the current outbreak is also unknown. It’s not even clear if it is transmissible, so it could be any number of things – from cold stress (temperatures were oddly cold when this event hit), to a pollutant, to runoff from recent heavy rainfall, to upwelling, to any number of microbial (and macrobial) agents. There is currently no data to support any hypothesis for its etiology.

Because often the timing of mass mortality events is incongruent with funding, and since there are no existing samples from the last Diadema mass mortality, the team has sprung into action – with the generous support of Cornell’s Atkinson Center for Sustainable Futures – to ensure that scientists in the region have supplies and opportunities to capture this important event and preserve material which is amenable to wide downstream analyses to determine its cause – everything from molecular microbiology to biochemistry to oceanography and veterinary histopathology.

Working with the Atlantic and Gulf Rapid Reef Assessment (AGRRA) network, the team along with scientists in Florida, Hawaii, and at several institutions in the Caribbean brainstormed ideas for what to collect to allow meaningful analyses. The first “kits” to sample specimens were deployed in early April to the Caribbean Netherlands island of Saba, where a collaborator (Alwin Hylkema) was organizing a workshop on Diadema aquaculture. Following this first sampling, kits were sent to the lab of Marilyn Brandt (Moriah Sevier) at the University of Virgin Islands. Ian was very fortunate to be able to travel to Saint John (USVI) to participate in sampling of urchins in late April, since this fell in the middle of teaching 2 classes!!

Heading down there was incredibly valuable, since it can be difficult to get a sense of the scale and environmental interactions of any marine mass mortality event from Ithaca. On the first day, the UVI divers and Ian traveled to Saint John, working from the National Parks office, to process grossly normal specimens from a site with no observed mass mortality; on the second day, Ian and the UVI crew traveled to Saint John again to sample specimens at an affected site.

The condition affecting Diadema is certainly dramatic, and different from sea star wasting (on which the team worked for over 8 years). For a start, affected urchins catastrophically die – they lose their spines and become a test (shell) very rapidly. Sea stars affected by sea star wasting sometimes developed lesions and then recovered, and sea star wasting described a myriad of signs from deflation to limb unco-ordation, to discoloration. Urchins have unusual behavior before they die, but this appears limited to only a few types of behavior. Hence, identifying what comprises an abnormal specimen is simpler for urchins than for sea stars.

After returning to Ithaca, Ian and Chris set about preparing sequencing libraries from these initial samples – which will broadly look at gene expression and some types of potentially pathogenic agents. The first set of these was just submitted! So fingers crossed for more info soon.

Since coming back from Saint Thomas, Ian has deployed additional kits to sample specimens widely across the region, and importantly to work with scientists in these countries, including to Antigua and Barbuda, Grenada, Jamaica, Mexico, as well as sampling grossly normal animals in Florida. These will shortly be augmented with kits to Barbados, Cayman Islands and Turks and Caicos to bracket geography of the condition.

Stay tuned for more updates in coming weeks!

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