Marine scientists from the De La Salle University (DLSU) Manila found ways to preserve the wonders of the Tubbataha Reefs Natural Park as they also warned that continued nutrient buildup can greatly reduce the coral cover and diversity of the reef in the coming years.
The Tubbataha Reef in the Sulu Sea is globally renowned for its high coral diversity. Recently, however, its status as a global benchmark for reef conditions within a marine protected area is under threat by notable changes in its residing species.
"These changes are small but significant and may presage a continuing decline in corals," said Dr. Wilfredo Y. Licuanan, a biology professor at DLSU and the founding director of the Br. Alfred Shields FSC Ocean Research Center.
Hard coral cover in four study sites shrunk by 1.1% per year from 2012 to 2019, as algal cover expanded by 1.9% over the same period. Rocky spaces for coral growth are steadily being overrun by sponges and cyanobacteria or “blue-green algae.”
Shifting conditions are most consistently seen at the South Atoll, where lagoon waters drain through during low tide. The atoll, which is already prone to damage from drifting logs and metal buoys, is also exposed to rising ocean temperatures and acidity.
These low-key changes may indicate that the area is slowly becoming “eutrophic,” wherein buildup of nutrients from “guano” or seabird droppings would trigger the bloom of species that can seriously affect coral survival, growth, and reproduction.
Sponges and algae can outcompete coral larvae for space to settle and impair the photosynthesis of symbionts that supply oxygen to corals, while the crown-of-thorns starfish aggressively feed on coral polyps.
Despite this alarming development, Dr. Licuanan is confident that the Tubbataha Reef—with its large size, a considerable population of algae-grazing species, and a high level of larval connectivity—can manage to withstand such risks.
Enhanced monitoring and management practices, he believes, would be the key—even amid the disruptions brought about by the COVID-19 pandemic. "Fortunately, the Tubbataha Management Office was able to continue the monitoring, but they require the help of additional scientific expertise and instrumentation.
The full article of the study “Changes in Benthic Cover in the South Atoll of Tubbataha Reefs due to Possible Eutrophication” will be published online by the Department of Science and Technology in Vol. 150 of the Philippine Journal of Science (philjournalsci.dost.gov.ph). The photos were taken from the said paper.
Map shows the Tubbataha Reefs Natural Park and study sites.
Close-up images of the cyanobacteria (dark brown) and sponges (light gray) overgrowing corals (light brown) resulting from the nutrient buildup in Tubbataha Reef.
A patch of coral-killing sponge (dark gray; measuring about 5 m x 1 m) sustained by the nutrient buildup in Tubbataha Reef.
By Allyster A. Endozo, DOST-STII