|A coral colony tagged on May 26 is not bleached.|
The good news is that almost all of the corals are still hanging on. They are going it alone though, their symbiotic algae mostly gone. When we look closely as the surface of the bleached corals, the coral polyps are stretching their tentacles out into the water, grasping for food.
By June 1st, the same colony as above has lost most of its
color, appearing bleached. The green on top of the colony
is a layer of mucus.
Another possibility is that the corals are not getting enough food without their symbionts and are burning through their fat reserves. If this is the case, the clock is ticking for these corals until those fat reserves run dry. The question is whether these corals can continue to feed themselves, or live off their fat reserves, long enough to acquire new symbionts.
A mucus layer shedding off a bleached coral. Notice the
white color of the coral where the mucus has fallen away.
The thousands of tiny white bumps are the living coral
The coral colonies that are bleaching on Dongsha are spewing out mucus, which coats the colony. Producing lots of mucus is a general coral stress response, the mucus may be a way for the coral to shed its symbionts or harmful bacteria.
When we first observed bleaching on May 26, it was only massive, dome-shaped corals of the genus Porites. Now we are beginning to see the start of bleaching in different species of branching coral.
|Bleaching is starting in several different species.|
Recent coral mortality. A thin layer of algae is covering the
We will continue to keep an eye on the bleaching happening on Dongsha, keep following our blog for more updates in the weeks to come.
- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution
Temperature recorded by a logger on the Dongsha
reef flat. The sharp up and down spikes are daily
temperature changes. The 4-5°C warming trend
beginning around May 9th likely caused the
bleaching event on Dongsha.
Partial bleaching of branching