Reef Tribe Join The Reef Tribe

Reef Map · Mindanao

Sulu Archipelago and Tawi-Tawi

The Sulu–Sulawesi seascape at the southern edge of the Coral Triangle

About 1,218 words · 20 numbered sources · Updated 2026-11-13

Hundreds of islands and some of the country's largest reef systems between Mindanao and Borneo. Market surveys by Mindanao State University in Tawi-Tawi record the richest commercial reef-fish fauna in the Philippines, alongside the Turtle Islands green turtle rookery, yet the reefs remain among the least studied in the country.

Geography and reef types

The Sulu Archipelago runs south-west from the Zamboanga Peninsula towards Borneo. It divides the Sulu Sea from the Celebes (Sulawesi) Sea. Its southern half is the province of Tawi-Tawi, which Mindanao State University–Tawi-Tawi College of Technology and Oceanography (MSU-TCTO) researchers describe as having more than 300 islands and huge reef systems at the heart of the Coral Triangle 1. Habitats range from reefs around islands such as Bongao to wide intertidal flats and seagrass, such as the Pagasinan tidal flat surveyed for sea cucumbers 12. The six islands of the Turtle Islands Wildlife Sanctuary lie in the far west of the province and straddle the border with Malaysia 6,7.

The archipelago is part of the Sulu–Sulawesi Marine Ecoregion, shared by the Philippines, Malaysia and Indonesia. Fisheries and migratory species cross national borders here, which makes management across borders necessary 13,14.

Biodiversity

The clearest data on biodiversity come from fish markets. Muallil et al. (2020, MSU-TCTO with UP Diliman and UP Mindanao) surveyed markets in Tawi-Tawi from October 2015 to December 2018 for 11 groups of commercially important reef fishes 1. They recorded 266 species, led by groupers (48 species), snappers (40) and surgeonfishes (33). The same groups yielded only 159 species in Palawan and 139 in Panay, and Tawi-Tawi had about five times more unique species than either 1. The catch included four species listed as Vulnerable by the IUCN: the bumphead parrotfish Bolbometopon muricatum, the groupers Epinephelus fuscoguttatus and E. polyphekadion, and the squaretail coral grouper Plectropomus areolatus 1. The authors conclude that Tawi-Tawi and the Sulu Archipelago are the richest in the Philippines for commercially important reef fishes 1. The same team has published length–weight data for 161 reef fish species to support biomass surveys 2.

New molecular tools are filling gaps. MSU-TCTO, MSU-Iligan Institute of Technology and Ehime University have published environmental DNA (eDNA) baselines for marine fishes and decapod crustaceans in Tawi-Tawi 3,4. These methods let researchers sample biodiversity from seawater, which helps where diving surveys are hard to run.

The Turtle Islands Wildlife Sanctuary is part of the largest green turtle nesting ground in ASEAN, with nesting all year round 6. Bird surveys of its six islands recorded 44 species, including the Vulnerable grey imperial pigeon and the Philippine megapode. Only Baguan Island retains mature beach forest 7. Seagrass and seaweeds are also central. Nearly all of 280 people interviewed in Tawi-Tawi coastal communities eat seaweed 8.

Threats

  • Fishing pressure. Commercially important reef fishes are the backbone of local diets and markets, and several Vulnerable groupers and the bumphead parrotfish appear regularly in catches 1. A fisheries assessment of Tandubas, Tawi-Tawi, describes fishing as the main livelihood of coastal residents 17.
  • Turtle egg poaching. Fischer, Trono and Salinas (2021) found that the illegal turtle egg trade in the Turtle Islands was still ongoing, driven by poverty. Livelihood projects in the late 1990s and early 2000s had not lasted 6.
  • Habitat shift. Living coral is giving way to dead coral and algae on monitored reefs 9.
  • Tourism hotspots. At Great Santa Cruz Island off Zamboanga City, a study linked visitor anchoring and littering at the "pink beach" to reef degradation 18.
  • Limited data. The region's remoteness and limited research funding mean that reef condition is often inferred from markets, eDNA or short surveys rather than long time series 1,3,10.

Management and protected areas

The Turtle Islands Wildlife Sanctuary (242,958.29 ha) is among the largest legislated protected areas in the country under the Expanded NIPAS Act (RA 11038). The same schedule lists the Great and Little Santa Cruz Islands Protected Landscape and Seascape off Zamboanga City 19. The Turtle Islands are also part of the Turtle Islands Heritage Protected Area, set up under a memorandum of agreement between the Philippines and Malaysia 5,20.

Regional frameworks cover the wider seascape. Pomeroy et al. (2019, with Palawan State University) discuss scaling the ecosystem approach to fisheries management in South-east Asian seas, including the Sulu–Sulawesi 13. Ellett, Thomsen and Besançon (2025) identify barriers to, and openings for, transboundary marine management in the seascape 14.

Local capacity is growing. MSU-TCTO in Bongao runs fisheries and marine science programmes, and its researchers lead most of the recent peer-reviewed work on Tawi-Tawi's reefs and fisheries 1,2,3,10.

Key research and studies

  • Market-based biodiversity inventories. Muallil et al. (2020) and the length–weight dataset (2023) by MSU-TCTO 1,2.
  • eDNA baselines. MSU-TCTO, MSU-IIT and Ehime University (2026) 3,4.
  • Reef invertebrate change. Genito and Campos (2013, UP Visayas) 9.
  • Coral transplantation outcomes. Samaniego et al. (2023), including Bongao 11.
  • Turtle Islands. Livelihood, poaching and bird surveys 6,7, and the transboundary heritage area 5,20.
  • Seaweed and coastal food systems. A survey of seaweed consumption in coastal communities 8.

Restoration work

Published restoration results for the archipelago are limited to coral transplantation sites under the national programme. The Bongao result is among the strongest fish responses reported in that evaluation 11. The authors caution that transplantation effects are hard to detect without sound study design, and that the evidence remains thin 11.

For the Sulu Archipelago, the most valuable next steps may be monitoring rather than building. That means permanent reef transects run by MSU-TCTO and partners, regular eDNA sampling 3,4, and market monitoring of Vulnerable groupers and bumphead parrotfish 1. Linking turtle conservation to lasting livelihoods, as Fischer et al. recommend, is also likely to protect nesting beaches and nearby reefs better than any single restoration project 6.

Open research questions

  1. Baseline coral condition. What is the current hard coral cover across Tawi-Tawi's major reef systems, and how did they fare in 2024 9,15?
  2. Why so many fish species? What explains Tawi-Tawi's higher commercial fish richness compared with Palawan and Panay: habitat extent, connectivity with the Celebes Sea, or lower fishing pressure 1?
  3. Sustainable catches. Are the Vulnerable groupers and bumphead parrotfish in Tawi-Tawi markets being fished sustainably 1,10?
  4. eDNA versus diving surveys. How well do eDNA inventories match visual census and market data 1,3,4?
  5. Transboundary connectivity. How strongly are Sulu Archipelago reefs linked by larvae to Sabah and the Celebes Sea, and how should that shape joint management 13,14?
  6. Restoration evidence. Do the Bongao transplantation gains persist, and can they be repeated 11?

References

  1. Muallil RN, Tambihasan AM, Enojario MJ, Ong YN, Nañola CL (2020). Inventory of commercially important coral reef fishes in Tawi-Tawi Islands, Southern Philippines: the Heart of the Coral Triangle. Fisheries Research 230: 105640. Mindanao State University–Tawi-Tawi College of Technology and Oceanography, UP Diliman and UP Mindanao. https://doi.org/10.1016/j.fishres.2020.105640
  2. Muallil RN, Tambihasan AM, Enojario MJ, et al. (2023). Data on the length-weight relationship of 161 species of commercially important coral reef fishes in Tawi-Tawi islands, Southern Philippines. Data in Brief 50: 109537. MSU-TCTO. https://doi.org/10.1016/j.dib.2023.109537
  3. Pinsoy KMG, Watanabe K, Logronio DJ, Delostrico RQ, Ajik MNH, Pedrosa-Gerasmio IR (2026). Environmental DNA (eDNA) metabarcoding for marine fish biodiversity: advancing non-invasive monitoring techniques in Tawi-Tawi, Philippines. Ocean & Coastal Management 278: 108230. MSU-TCTO, MSU-IIT and Ehime University. https://doi.org/10.1016/j.ocecoaman.2026.108230
  4. Delostrico RQ, Watanabe K, Logronio DJ, Pinsoy KMG, Pedrosa-Gerasmio IR (2026). Decapod crustacean biodiversity in Tawi-Tawi, Philippines: a baseline assessment using environmental DNA (eDNA) metabarcoding. Estuarine, Coastal and Shelf Science 341: 110134. MSU-IIT and Ehime University. https://doi.org/10.1016/j.ecss.2026.110134
  5. Miclat E, Nunez E (2016). The Philippines–Sabah Turtle Islands Heritage Protected Area (TIHPA). Book chapter, Routledge. https://doi.org/10.4324/9781315724270-16
  6. Fischer C, Trono R, Salinas RAF (2021). Addressing gaps in socio-economic and natural assets to halt marine turtle egg poaching: a livelihood feasibility study in the Turtle Islands Wildlife Sanctuary, Philippines. Global Ecology and Conservation 32: e01913. https://doi.org/10.1016/j.gecco.2021.e01913
  7. Paguntalan LMJ, Canag JF, Oporto D, Jakosalem PG, Cruz MDS, Fernández G (2021). Bird surveys in Turtle Islands Wildlife Sanctuary, Philippines. The Palawan Scientist 13: 101–117. https://doi.org/10.69721/tps.j.2021.13.2.08
  8. Tahiluddin AB, Esmola FR, Abduraup SA, Camsain AMB, et al. (2025). Seaweed consumption practices in coastal communities of Tawi-Tawi, Philippines. Phycology 5: 25. https://doi.org/10.3390/phycology5020025
  9. Genito GE, Campos WL (2013). Temporal patterns of reef macroinvertebrate communities, Tawi-Tawi, Philippines. Galaxea, Journal of Coral Reef Studies 15: 143–153. UP Visayas. https://doi.org/10.3755/galaxea.15.143
  10. Muallil RN, Injani AS, Habibuddin AA, Ong YN, et al. (2026). Coral reef fish biomass and exploitation status in the Tawi-Tawi Islands, Southern Philippines: implications for management and conservation. Preprint (SSRN), not peer-reviewed. Mindanao State University and UP Mindanao. https://doi.org/10.2139/ssrn.6108500
  11. Samaniego BR, Ancog R, Nacorda HME, Hernandez H, Corales MC, Balatayo AG (2023). Indications of enhancement of reef fish community richness at selected coral rehabilitation sites in the Philippines. Journal of Environmental Science and Management 26 (2). UP Los Baños. https://doi.org/10.47125/jesam/2023_2/05
  12. Ajik JO, Ajik MNH, Tahiluddin AB, et al. (2021). Population density, distribution, and species composition of sea cucumbers in Pagasinan tidal flat, Tawi-Tawi. The Philippine Journal of Fisheries 28 (2). https://doi.org/10.31398/tpjf/28.2.2021-0008
  13. Pomeroy RS, Garces LR, Pido MD, Parks JE, Silvestre GT (2019). The role of scale within an ecosystem approach to fisheries management: policy and practice in Southeast Asian seas. Marine Policy 106: 103531. Palawan State University and partners. https://doi.org/10.1016/j.marpol.2019.103531
  14. Ellett LG, Thomsen JM, Besançon C (2025). Potential barriers and windows of opportunity for transboundary marine management in the Sulu-Sulawesi Seascape: a policy analysis. Marine Policy 171: 106473. https://doi.org/10.1016/j.marpol.2024.106473
  15. NOAA Coral Reef Watch. Regional Virtual Station time series: Southern Philippines (1985–present). https://coralreefwatch.noaa.gov/product/vs/data/southern_philippines.txt
  16. NOAA Coral Reef Watch. Methodology, product description and data availability for the daily 5 km products. https://coralreefwatch.noaa.gov/product/5km/methodology.php
  17. Mohammad HS, Ebbah J, Sahiyal K, et al. (2022). An assessment of small-scale fisheries in Tandubas, Tawi-Tawi, southern Philippines. Menba Journal of Fisheries Faculty. https://dergipark.org.tr/tr/pub/menba/issue/70523/1082445
  18. Zabala C (2023). Impact of pink beach tourism on the marine ecosystem of Great Santa Cruz Island, Zamboanga City. Lex Localis: Journal of Local Self-Government. https://doi.org/10.52152/mbsyn411
  19. Republic of the Philippines (2018). Republic Act No. 11038, Expanded National Integrated Protected Areas System Act of 2018 (schedule of protected areas). https://elibrary.judiciary.gov.ph/thebookshelf/showdocs/2/84999
  20. Government of the Philippines and Government of Malaysia (published 2002). Memorandum of agreement on the establishment of the Turtle Islands Heritage Protected Area. Journal of International Wildlife Law and Policy 5(1–2): 157–161. https://doi.org/10.1080/13880290209354004

Every source above was opened and checked when this page was written. Philippine university authorship is noted where it applies. Figures are quoted from the cited source and are not independently re-measured. This page is a research overview, not legal or management advice.

Other regions