Corals are small colonial animals that secrete hard outer skeletons. One of the principal corals for building reefs in Hawaii, known as rice coral, Montipora capitata, spawn for four nights after each new moon from May through August.
Scientists with the U.S. Geological Survey (USGS), the University of Hawaii, the Hawaiian Division of Aquatic Resources, the Maui Ocean Center, and the University of Washington are trying to learn how waves, currents, and seawater properties affect the dispersal of coral larvae.
Dr. Curt Storlazzi, USGS’s chief oceanographer for the project, said the scientists used high-tech instruments to track the coral larvae’s night journey.
The packets of eggs and sperm rise to the ocean’s surface and float along by the millions in surface currents until the fertilized eggs, or larvae, sink and start to grow on rocky areas. The problem is, said Storlazzi, no one knows exactly where the currents take the larvae.
As researcher Eric Brown of the University of Hawaii explains, "Some coastal areas may not be developing coral reefs simply because the larvae are unable to settle."
Where the larvae go is what the USGS scientists and their collaborators aim to determine. The researchers used underwater tripods that look much like lunar landers to monitor temperature, water clarity, waves, and currents.
At the same time, satellite tracked drifters were released at night to float along with the larvae, and the researchers monitored the drifters’ positions all night on radio frequencies.
Storlazzi noted that the currents off West Maui are complex, and understanding the fate of the larvae requires scientists to monitor currents for days to detect shifts due to changes in tides and wind.
Storlazzi will round out the experiment by measuring water speeds along the coast from a boat using an acoustic doppler current profiler.
The USGS Coral Reef Team, led by Dr. Michael Field, has been studying the effects that current movements and sediment particles have on the condition of Hawaiian coral reefs for the past several years to provide resource managers with information on how to best protect these Hawaiian reefs.
Field says, "Our goal has been to identify the pathways of sediment to the reef, and how it is moved onto corals by waves and currents." After several years of research on the islands of Maui and Molokai, the USGS team is applying their expertise to the tracking of microscopic larvae.