Coral reefs in the Virgin Islands recovering from an unprecedented bleaching event last year, now are likely suffering from a disease known as white plague.
When we saw the extent and severity of the bleaching in September of last year, we were all very concerned about the downstream long term effects that it would have on the reefs, said National Park Service fisheries biologist Jeff Miller.
Were starting to get some of that data now, and it looks like the reef is being substantially affected by the bleaching and by a post-bleaching disease, added Miller.
Although there is no definitive test to determine if a reef is suffering from white plague disease, the external symptoms of V.I. reefs appear to point toward this bacteria.
Many factors about the recent bleaching and disease are unique, according to U.S. Geological Survey Marine Ecologist Dr. Carolyn Rogers.
Its unprecedented in the sense that this is the worst bleaching episode that weve ever had here, Dr. Rogers said. The bleaching started severely in September and October.
We began to see some recovery in the corals, and then they were hit by disease, the marine expert continued. Its more severe than ever.
Last years bleaching event was also unique because for the first time elkhorn coral suffered from the episode, Rogers added.
Its unprecedented in that the bleaching is the worst that weve seen, and this is the first time weve seen elkhorn coral bleach, said Rogers.
Although corals can recover from bleaching, the white plague bacteria are causing the reefs to continue to suffer, according to experts.
Weve had several outbreaks of disease mortality several times, but none of them have been associated previously with bleaching events, said Miller. What we dont understand is the connection between the two.
The hypothesis is that the extensive nature of this bleaching episode made the corals more susceptible to the patho-gens that cause the disease, he added. Its been kind of a one-two punch.
Research Is Difficult
When it comes to the bleaching and disease, not much is known, and not much can be done to save the coral from these problems.
Coral is very difficult to do research on, said Dr. Rogers. Theres not very much known about them. Theres some indication that disease can be related to things like sewage runoff, but were seeing disease in places where theres nothing thats obviously causing it.
Were still at such an infancy with this, Miller added. Its exceptionally hard to understand and to figure out why or how corals get sick. But that doesnt mean we just throw our hands up and say that theres nothing we can do.
Both Rogers and Miller acknowledged they were disturbed by the recent suffering of the V.I. coral reefs.
Reefs in Crisis
In this case, the combination of the bleaching and the disease has been followed by really the worst mortality that Ive seen, said Rogers. It is true to say that the reefs in the Virgin Islands are in crisis right now. Its a very disturbing thing for all of us who work on these things to see.
Were having such extensive mortality of such slow-growing, long-lived corals with a low reproductive output, Miller added. Theyre dying in very high numbers, very fast. Ive never seen anything like it in my 21 years of work.
One of St. Johns worst affected reefs is the Tektite Reef at Great Lameshur Bay.
My focus in all of this is that what this means is we dont get discouraged, said Miller. It means we focus our efforts on what we can do about it.
The reefs are being monitored by the National Park Service and the U.S. Geological Survey, and the monitoring program in the Virgin Islands is one of the best, said Rogers.
One thing thats making it possible to quantify whats going on is that we monitor the same reefs and areas every month, or every year, she said. We have regular monitoring going on, so we know what they looked like before the bleaching and the disease. That does distinguish the research programs here from many other places; here, were actually able to say what is happening in pretty precise terms.
In some cases, the monitoring program has revealed troublesome data.
One site that is being monitored has shown approximately a 30 percent loss of coral cover as a result of last years bleaching and the recent disease, said Miller.
Weve been monitoring coral disease at that site monthly since 1997, he said. Weve had disease mortality at that site every month that weve monitored it.
Reefs Destroyed in Weeks
Because of the combination of bleaching and disease, Virgin Islands reefs that have been growing for hundreds of years are being destroyed in a short amount of time.
We are seeing that the major reef-building corals are being affected by this mortality, said Miller. They grow about a millimeter a year, and the reefs that we see today have taken many hundreds, if not thousands, of years to grow. Theyre dying in a matter of months, and weeks in some cases.
Previous cases of coral deaths have been limited to specific species and depths. The most recent mortality is being seen across all depth zones, from shallow, to moderate, to deep.
Although not much can be done about the disease affecting the reefs, humans can minimize the damage that they contribute. One important point is, because the reefs are under so much stress already, its especially important not to add to that, said Rogers. They obviously have suffered quite a lot of deterioration, so its especially important not to allow sediment to run into the water during all the construction that is going on and to avoid anchor damage. Everything people do that adds insult to injury can make a difference and can result in a coral dying that wouldnt ordinarily die.
In addition to sediment runoff and anchor damage, people should not touch reefs while snorkeling or diving. Overfishing can also harm coral.
These are all manageable aspects of the resource protection, said Miller. The reefs certainly need our protection. We need to work on compliance with all the CZM (Coastal Zone Management) laws and the building codes that require certain sediment control practices to the highest degree possible.
Neither Rogers or Miller speculated on what the future holds for Virgin Islands coral reefs.
I think the reefs of the V.I. are going through a change right now, said Miller. Geologically speaking, this is a blip in time.
We really are not sure whats going to happen next August and September, said Rogers. Were really hoping we dont see a repeat of this.