|Satellite View of Helen Reef|
We just completed our work at Helen Reef, the southernmost of Palau's reefs. Helen Reef is rather isolated from any large mainland, inside the atoll is a small island less that half a square kilometer in size, uninhabited, except for three rangers who patrol the reef's marine protected area. The closest other island is Tobi Island, which has a population of less than 100.
The coral reefs at Helen suffered greatly during the 1998 El Niño year, which led to bleaching events worldwide. El Niño years result in warmer waters and temperatures. Bleaching occurs when corals lose their endosymbiotic algae, Symbiodinium, due to stress, usually extremely hot temperatures. The colors of corals are actually a result of the pigmentation in this algae, so when corals lose their symbionts the colonies appear white, as the calcium carbonate skeleton becomes visible through the coral's naturally translucent tissue - hence the term bleaching. If temperatures return to normal and the stress ceases in time (at most a few weeks), corals can re-acquire their algal symbionts and return to a healthy state; however, if they remain bleached for too long, colonies can die as they starve without the input of carbohydrates that their algae typically provide.
|Example of a bleached coral |
colony in Dongsha Atoll
Photo credit: T. De Carlo
Much of the monitoring efforts implemented in Palau were a response to the extensive coral bleaching that occurred during 1998. Thanks to these efforts we now have data following the recovery, or lack thereof, of reefs from that time period thru today. Helen's reefs suffered dramatically during this event, but made a quick and remarkable come back, making Helen Reef an important site to characterize and understand. During our time here we collected samples and conducted surveys at various different habitats including the outer reef crest, inner reef and the channel that leads into the lagoon of Helen's atoll (the channel is the squiggly line in the satellite view above).
|Corals at Helen Reef|
Photo credit: H. Rivera
|Coral diversity at Helen Reef|
Photo credit: H. Rivera
|Wreck on Helen Reef|
During our dives we found colorful and diverse reefs, thriving with life. In our first dive on the outer reef, two small reef sharks greeted us as we swam from our boat over the drop off towards the reef, which was dominated by branching corals and small fish. On our way to the second dive site a pod of dolphins followed us into Helen's lagoon, jumping over the rough waves that are typical of Helen's NW side, where several wrecks in the distant attest to the dangers of running aground onto a coral reef. In our second dive site we found plenty of massive Porites, great for our coring and tissue sampling needs. Our second day of diving was likewise full of great dive sites, with good coral, a testament to Helen Reef's resilient recovery from previous bleaching events. Overall, our work here was a success and the diving spectacular. We even got to visit the ranger's island, but I'll tell you all about that in the next post. Next stop: Kayangel.