Enhanced monitoring of the globally renowned Tubbataha Reef in the Sulu Sea is required for its continued preservation, marine scientists from the De La Salle University (DLSU) said.

The scientists warned that continued nutrient buildup can greatly reduce the coral cover and diversity of the reef in the coming years.

Sponge - Enhanced monitoring needed to preserve Tubbataha Reef in Sulu Sea
A patch of coral-killing sponge (dark gray; measuring about 5 m x 1 m) sustained by the nutrient buildup in Tubbataha Reef. (PHOTO VIA DHEL NAZARIO / MANILA BULLETIN)

The Tubbataha Reef 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.

According to him, hard coral cover in four study sites shrunk by 1.1 percent per year from 2012 to 2019, as algal cover expanded by 1.9 percent over the same period. Rocky spaces for coral growth are steadily being overrun by sponges and cyanobacteria or “blue green algae.”

Cyanobacteria - Enhanced monitoring needed to preserve Tubbataha Reef in Sulu Sea
Close-up images of the cyanobacteria (dark brown) and sponges (light gray) overgrowing corals (light brown) resulting from the nutrient buildup in Tubbataha Reef.

He added that 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.

Licuanan said that these low-key changes may indicate that the area is slowly becoming “eutrophic” in which buildup of nutrients from “guano” or seabird droppings would trigger the bloom of species that can seriously affect coral survival, growth, and reproduction.

He explained that 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, 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 to preserving it even amid 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,” he said.

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