West Philippine Sea and Benham Bank Stand Out in Global Study of Soft Coral Diversity

Philippine Reefs Emerge as Centers of Soft Coral Diversity

More than 4,400 soft coral samples from over 40 countries have helped place the West Philippine Sea and Benham Bank in the Philippine Rise among the richest habitats for zooxanthellate soft corals. An international study published in Nature Scientific Reports in May 2024 identified the Philippine waters as part of a major center of diversity for these animals, whose flexible colonies are prominent features of the country's reefs.

The research, led by Dr. Catherine McFadden with an international team of marine scientists, mapped the diversity and geographic distribution of soft corals across the Indo-Pacific. Filipino researchers contributed samples collected between 2019 and 2021 from the Kalayaan Island Group, Western Palawan, Pangasinan, Puerto Galera and Benham Bank.

Three broad regions stood out as simultaneous centers of species richness and endemism: the Western Indian Ocean, the Western Coral Triangle, which includes the Philippines, and the Northeast Australian Shelf. Species richness describes how many kinds of organisms live in an area. Endemism describes how restricted their distribution is, including species found only in a particular place.

The West Philippine Sea and Benham Bank showed diversity comparable to these global hotspots. Their soft coral communities include an extraordinary variety of species, many of which are likely still undiscovered. The findings give Philippine scientists a stronger basis for studying and protecting habitats that have received much less attention than reefs built by hard corals.

The challenge now reaches beyond identifying species. Climate change, damaging fishing practices, possible resource extraction and territorial tensions all affect the conditions in which research and conservation must take place.

What Makes Soft Corals Different?

Soft corals belong to the class Octocorallia. Unlike hard corals, which build the rigid skeletons that form the backbone of coral reefs, they grow as flexible colonies, often resembling small trees. Each colony consists of individual animals called polyps.

These corals do not produce the hard calcium carbonate skeleton associated with hard corals. Their branching forms still add complexity to reef habitats, creating shelter and breeding spaces for many other marine organisms. Protecting a reef therefore involves more than preserving its rigid framework: the living communities growing across it also matter.

Zooxanthellate soft corals live with microscopic algae called zooxanthellae. The algae use sunlight to produce energy through photosynthesis and share that energy with their coral hosts. This relationship, known as symbiosis, helps sustain the corals and contributes to the productivity of the reef around them.

Soft corals also have economic and medicinal value. Some species produce biologically active compounds with potential pharmaceutical uses. Their varied colors and forms attract divers, supporting ecotourism in places such as the Philippines.

For coastal communities, the importance of these animals extends from the habitats they help create to the fisheries and tourism activities associated with healthy reefs. Their scientific value is also considerable, particularly where researchers are still working to identify the species present.

How DNA Helped Map Hidden Diversity

McFadden's study represents the most comprehensive effort to date to map the biodiversity and biogeography of zooxanthellate soft corals. Biogeography examines where organisms live and how their distributions vary between places.

The researchers used DNA barcoding to compare specimens. This technique examines genetic information to help distinguish organisms that can be difficult to identify through appearance alone. The team grouped specimens into molecular operational taxonomic units, or MOTUs, which served as practical substitutes for species identification in the analysis.

Those genetic groupings allowed scientists to investigate both diversity and endemism across the vast Indo-Pacific. For soft corals, whose identification requires specialized knowledge, the approach provided a way to compare thousands of samples within a common framework.

Dr. Jue Lalas and Dr. Maria Vanessa Baria-Rodriguez, researchers at the University of the Philippines Marine Science Institute, were among the Filipino contributors. Their team collected all the Philippine samples used in the study, bringing several distinct Philippine reef areas into the international comparison.

The research sequence spans several years:

• 2019 to 2021: The Philippine team collected soft coral samples from the Kalayaan Island Group, Western Palawan, Pangasinan, Puerto Galera and Benham Bank.
• May 2024: The international study was published in Nature Scientific Reports, drawing on more than 4,400 samples from over 40 countries.

Lalas, a co-author of the study, described the Philippine contribution and the geographic importance of the findings:

The samples from the Philippines were major representatives for the Coral Triangle region. The paper shows that the Philippines, including the West Philippine Sea and Benham Bank in northeastern Philippines, is part of one of the centers of zooxanthellate soft coral diversity.

Why So Much Remains Unknown

Philippine reefs can contain abundant soft corals while still having relatively little research devoted to them. Lalas pointed to the small number of scientists working on the group as a central reason for that gap:

There are just very few papers on soft corals in the Philippines, despite them being obviously dominant components of Philippine coral reefs. One of the reasons for this is just the lack of people working on this group, as compared to hard corals.

Hard corals have historically attracted more research attention and funding. Their rigid skeletons and their role in building reefs make them easier subjects for many kinds of study. Soft corals present more difficult identification and classification tasks, requiring specialized training and experience.

The Philippines has also had relatively few specialists in soft coral taxonomy and ecology. Taxonomy is the work of identifying, naming and classifying organisms; ecology examines how organisms interact with their surroundings. Both are needed to understand which soft corals occur on a reef and how those communities change.

Baria-Rodriguez and her team at the UP Marine Science Institute's IMBiBE Laboratory have organized training with international specialists, including Dr. Yehuda Benayahu. These sessions aim to build Philippine expertise in soft coral identification and research.

The training is gradually expanding the country's knowledge base and encouraging a new generation of coral scientists. Lalas and Baria-Rodriguez are optimistic that continued research, training and international cooperation will lead to further discoveries.

Benham Bank's Deep, Diverse Reef

Benham Bank is an underwater seamount off the eastern coast of Luzon, with its shallowest area about 50 meters below the sea surface. Within the Philippine Rise, it supports one of the richest mesophotic coral ecosystems documented in the Philippines, with high biodiversity and relatively untouched reefscapes.

Mesophotic coral ecosystems occupy deeper waters where sunlight still reaches the seabed. At Benham Bank, clear water allows light to penetrate far enough to support corals and algae. Stratification, in which the water column forms distinct layers, also contributes to protective conditions around the reef.

Surveys have documented at least 11 genera of hard corals and 10 genera of soft corals, together with several types of macroalgae and a variety of sponges. A genus is a classification group that can contain several related species. Macroalgae are larger algae, rather than the microscopic algae living within coral tissues.

Researcher Joey P. Cabasan described why underwater mountains such as Benham Bank can support so much marine life:

Seamounts, in general, are known for having high biodiversity and unique benthic structures. Seamounts enhance ocean productivity and are considered biodiversity hotspots.

Benthic structures are features of the seabed and the communities living on it. At Benham Bank, these habitats also provide breeding and nursery areas for commercially important fish, connecting the health of a remote reef to fisheries and food security.

What Surveys Found Beneath the Surface

Benham Bank's diversity is visible in both the amount of coral present and the range of habitats recorded. Surveys across depths of 50 to 80 meters have recorded hard coral cover as high as 30%, while some individual sites have reached nearly 100%. Such extensive cover is exceptional for mesophotic reefs.

Researchers have identified eight distinct habitat types, ranging from areas dominated by macroalgae to zones dominated by octocorals. These differences mean that protecting the bank requires attention to a varied underwater landscape, rather than a single uniform coral habitat.

More than 60 fish species associated with reefs have been documented, including commercially valuable snappers, groupers and tunas. Together with the bank's role as a breeding and nursery area, those findings make its conservation relevant to people who depend on marine resources.

Ocean currents may also connect Benham Bank with reefs elsewhere in the Pacific. The North Equatorial Current could help move coral larvae between locations. Such exchanges may support recovery and resilience across the region by allowing young corals to reach other reefs.

The bank's remote location and depth have so far shielded it from the worst effects of human activity. Those same characteristics make research difficult. Expeditions require extensive planning, coordination among government agencies and specialized equipment.

Recent studies have nevertheless established valuable baseline information about the bank's biodiversity and ecological conditions. That starting record can guide decisions on protected zones, sustainable fishing and future research priorities, while giving later surveys a basis for measuring change.

Soft Corals Can Reveal Environmental Stress

Soft corals are also useful to scientists studying changes in reef condition. Studies at some disturbed or degraded sites across the Indo-Pacific have recorded a shift toward soft coral dominance, suggesting that these animals can withstand certain pressures better than hard corals.

Rising sea temperatures, pollution and overfishing are among the stresses associated with changing reef communities. When soft corals become more prominent, researchers can examine that shift alongside other measurements to understand how the habitat is responding.

Lalas explained both their capacity to survive disturbance and the limits of that resilience:

In some disturbed sites in the Indo-Pacific, some studies have reported a shift to the dominance of soft corals. They have been generally reported to have high resilience to disturbances. However, soft corals may also eventually be subjected to mortality if stressors persist. Overall, soft corals can serve as useful indicators of environmental disturbances. Ongoing research continues to shed light on their ecological roles in coral reefs amid global and local changes.

Persistent or more intense stress can still kill soft corals and reduce their populations. Monitoring their abundance and condition therefore gives conservation teams another way to track environmental disturbance, alongside the condition of hard corals and other reef organisms.

Protection Faces Environmental and Political Pressures

The West Philippine Sea and Benham Bank face a range of conservation threats. Climate change brings rising sea temperatures, ocean acidification and more frequent severe weather events, all of which can threaten coral health and survival.

Illegal fishing and overfishing can damage delicate habitats and reduce the fish populations that depend on them. Destructive fishing practices create a particularly direct risk to coral communities and the shelter they provide.

Interest in mineral resources in the Philippine Rise creates another concern. Deep sea mining and other resource extraction could put the fragile ecosystems of Benham Bank at risk. Territorial disputes in the West Philippine Sea, particularly those involving China, also complicate efforts to enforce environmental protections.

The Philippines has established the Philippine Rise Marine Resource Reserve, one of the country's largest offshore marine protected areas. More comprehensive conservation strategies, backed by effective enforcement, are still needed as research reveals the area's global importance.

Only about 5% of the world's seamounts are currently protected. Against that backdrop, Benham Bank stands out as a model for protecting a valuable marine ecosystem before it experiences the worst effects of human activity and global environmental change.

Research Support Shapes Conservation Choices

Philippine soft coral research has received funding from the Department of Environment and Natural Resources-Biodiversity Management Bureau, the National Security Council, the University of the Philippines, and the Department of Science and Technology-Philippine Council for Health Research and Development. That support helps sustain research and conservation work over time.

Cooperation between Filipino scientists and international specialists is expanding the ability to identify soft corals, compare communities and investigate their ecological roles. The international study provides a broader setting for that work, linking Philippine samples with collections from more than 40 countries.

For conservation managers, the findings offer concrete information about what needs protection: diverse soft coral communities in the West Philippine Sea, multiple habitat types at Benham Bank, and deeper reefs that support commercially important fish. Continued monitoring can help guide where protection, fishing controls and further surveys are most needed.

The immediate task is to turn a growing scientific record into lasting care for these habitats. Sustained funding, trained researchers, cooperation and enforceable protection are central to preserving the marine diversity now being documented.

Key Points

• A study published in May 2024 analyzed more than 4,400 soft coral samples from over 40 countries and placed Philippine waters within a major global center of diversity.
• The Western Indian Ocean, Western Coral Triangle and Northeast Australian Shelf stood out as centers of both species richness and endemism.
• Philippine samples came from five areas surveyed between 2019 and 2021, including the West Philippine Sea and Benham Bank.
• Benham Bank surveys documented at least 11 hard coral genera, 10 soft coral genera, eight habitat types and more than 60 fish species associated with reefs.
• Soft corals support reef habitats, have tourism and potential medicinal value, and can help scientists monitor environmental disturbance.
• Climate change, destructive fishing, resource extraction risks and territorial tensions complicate conservation.
• Training, continued research, reliable funding and effective protection are needed to safeguard these diverse marine communities.