Something is destroying Long Spine sea urchins in U.S. Virgin Islands waters, and efforts are underway to find and disarm the killer.
Right now, it’s unclear whether the situation is an isolated, limited event or whether it is the start of a major calamity.
While sea urchins can be troublesome for swimmers, snorkelers and divers, they are essential to the health of coral reefs and the general marine ecosystem. The Long Spine is especially helpful, eating generous quantities of algae that could otherwise proliferate and smother corals.
“They are essentially the lawnmowers of the reef,” as University of the Virgin Islands professor Marilyn Brandt put it.
Reports of dead Long Spine (Diadema Antillarum) began circulating on social media earlier this month. Wednesday, the Department of Planning and Natural Resources issued a notice, asking help from the community in tracing the problem.
In the 1980s the entire Caribbean region experienced a major loss of Long Spine sea urchins. By some estimates, the region lost as much as 90 percent of the creatures at that time, Brandt said.
The cause of the 1980s die-off was never determined. Brandt said one of the more popular theories was that a pathogen was released into the heavily-trafficked waters at Panama, where ships typically dumped their ballast water, and that it traveled throughout the Caribbean.
It’s taken decades for the sea urchin population to recover, but, “They’ve been making a comeback,” she said.
All the sightings of dead and dying sea urchins so far have been in and around the southwest shores of St. Thomas, at Flat Cay, Black Point, Range Cay and Lindberg Bay. There are also reports from nearby Hassel Island that have not yet been confirmed.
Marine researchers have been checking out various sites around St. Thomas and St. John, but the work is time-consuming and the staff is small, so the findings are limited. They have found pockets of extensive sea urchin deaths as well as reefs that appear to be unaffected.
The worst-case scenario is that some new pathogen is making its way through V.I. waters. But Brandt offered a less drastic possibility.
It could be an “environmental event” rather than a disease, she said. Quick changes in water temperature, caused by rain or by a temporary change in currents, could stress the sea urchins, for example. Or an excess of stormwater runoff could stir up chemicals in the water and decrease oxygen levels.
“It may be related to the rain bursts that we’ve been getting lately,” she said. “We’re not sure that it’s a disease.”
She noted a curious element that may or may not prove significant. The known affected area is the same as the area where stony coral tissue loss disease first made its appearance in V.I. waters.
The first sighting of the coral disease was in January 2019 off St. Thomas’ southwest shore. In the three years since then, it has been found throughout the Virgin Islands.
Some sites have lost as much as 70 percent of their corals, said Brandt. On St. Croix, stony coral tissue loss disease is an epidemic now, she added. On St. Thomas, it is considered “endemic.” That is, “It’s here to stay.”
Efforts to control the coral disease by applying an antibiotic paste to areas at and near affected coral seem to be working, Brandt said. Researchers are working now to analyze whether that is true.
The defense against stony coral tissue loss disease has been a joint effort by professional and citizen scientists. Recreational and professional scuba divers have been key both in identifying areas of concern and in aiding in applying antibiotics.
Brandt said the network established in that fight, is already helping in the current situation.
“We really didn’t know about this (sea urchin kill) until a diver posted it on Facebook,” she said. Since then, divers have been sharing their information.
She stressed that divers should report sightings of healthy sea urchins as well as those that appear dead or damaged. That will help researchers to pinpoint trouble spots.
A release from the Department of Planning and Natural Resources urged people to submit photos here.