BENHAM BANK, on the Philippine Rise, hosts one of the Philippines’ richest coral ecosystems, including important fish species, marine researchers said.
They cited the potential for Benham Bank coral to play a role in restoring damaged coral reefs elsewhere in the Philippines.
The bank, one of the several seamounts in the Philippine Rise, a continental shelf extension off the east coast of the Philippines, contains one of the richest mesophotic or deep coral ecosystems despite being on the track of typhoons, according to researchers from the University of the Philippines Marine Science Institute.
The study cited the pristine state of Benham Bank’s reefscapes, with at least 11 hard coral genera of varying morphotypes, with four sites having excellent coral cover, 10 soft coral genera, at least four genera of seaweed, and some arborescent sponges.
The hard coral cover across the 50-80m depth range of Benham Bank was recorded at an overall mean of 30%, “being substantially higher than other tropical mesophotic coral ecosystems on isolated seamounts and those closer to mainland Philippines.”
Typically, live hard coral cover on mesophotic reefs is relatively poor, but the Benham Bank can “maintain high hard coral cover,” according to the study.
“Benham Bank is in a way resilient to physical and thermal stress. There is stratification or layers with different water properties, which perhaps protected the Benham Bank from the effects of stress,” according to Joey P. Cabasan, one of the researchers.
“The water at Benham Bank is very clear. Since there are no major sources of nutrients like large rivers, nutrients and chlorophyll in the water column are low, and light is able to penetrate to greater depths. This allows the corals and algae to thrive there,” according to fellow researcher Cesar L. Villanoy.
Benham Bank showed eight probable habitat types — macroalgae-dominated, octocoral-dominated, hard coral-dominated, hard coral and octocoral, turf algae and hard coral, turf algae-dominated, rocky, and sandy — that may need special protection via legislation.
Classifying the probable habitat types at the Benham Bank “could be helpful for legislators in properly zoning the area and determining which parts may be designated for protection, fishing, and other uses,” the researchers said.
Benham Bank, an underwater seamount taller than Mt. Apo. It is a three days’ travel by ship from the mainland Philippines.
The United Nations in 2012 declared Benham Rise as part of the Philippine continental shelf. In 2017, Manila renamed it the Philippine Rise and declared it a “protected food supply exclusive zone.”
The Philippine military last year flagged the loitering of Chinese research vessels in the area.
The researchers said during their fieldwork, they had seen traditional small-scale fisherfolk from Infanta, Quezon, working in the area.
Citing a 2014 survey, the study said Benham Bank, despite its depth, hosts more than 60 reef-associated fish species, many of which are commercially important food fish include large species of snappers, emperor breams, groupers, trevallies, and surgeon fishes.
It said the area also serves as an important breeding and nursery area for various tuna species and other commercially valuable fish.
Meanwhile, the study noted that Benham Bank is “affected by the North Equatorial Current, which potentially receives larvae from other Pacific islands,” Mr. Cabasan said.
The north equatorial current flows towards the northeast coast of the Philippines and splits northwards to form the Kuroshio or the Japan Current and southwards as the Mindanao Current, the researchers said.
“This current could mean that coral populations are connected, making coral reef recovery a possibility in mesophotic reefs with poor live hard coral cover.”
The research team, which underwent at least six months of preparations due to seasonal challenges such as monsoons, included various specialists, including marine biologists, oceanographers and geologists.
The team said since it was only able to study the Benham Bank area outside the monsoon season, “many recommendations can be made for further studies, such as exploring the potential seasonal variation in stratification.”
“A dedicated paper on the fish communities in the area can also provide a better picture of the ecological role Benham Bank plays,” it said.
The emerging threats at the Benham Bank, whether natural or manmade, must be studied to continue to preserve its “pristine state,” the team added, noting that only 5% of seamounts around the world are protected. — Kyle Aristophere T. Atienza
