27-07-2025
One of 1st real-world data sets shows how tropical marine life cope with acidifying seas
Published on: Sunday, July 27, 2025
Published on: Sun, Jul 27, 2025 Text Size: ARMS (Autonomous Reef Monitoring Structures) are stacked PVC plates that mimic the complex reef structures for marine organisms to colonise, which helps to monitor marine biodiversity of seabed at MERC, Gaya Island, over time. DRIVEN by climate change, oceans are absorbing more heat and carbon dioxide, causing a triple threat: warming waters, ocean acidification, and deoxygenation – a condition increasingly observed in coastal areas of Malaysia and across the tropics. In layman's terms: the oceans is getting Hotter, Sour and Breathless. The OA (Ocean Acidification) station at Merc (Marine Ecosystem Research Centre), launched on 1 February 2023, is pioneering long-term monitoring of reef changes linked to acidification. It fills a critical data gap in Southeast Asia and aligns with global efforts under the UN Decade of Ocean Science. On March 27, 2023, Merc was recognised by the Malaysia Book of Records a s the first OA monitoring station for South China Sea. Researchers have deployed Autonomous Reef Monitoring Structures (ARMS) and Calcification Accretion Units (CAUs). These devices mimic reef habitats and passively collect sessile (attached to or fixed in one place) and mobile invertebrates, allowing scientists to assess biodiversity changes over time without disturbing the environment. Using innovative tools like ARMS and CAUs, researchers are tracking not only corals but also hidden reef dwellers, including sponges, molluscs, bryozoans, and mobile invertebrates, which are essential for a healthy reef ecosystem. The ARMS and CAUs deployed by Centre For Marine & Coastal Studies (Cemacs), Universiti Sains Malaysia in 2023 (led by Prof. Dato' Dr Aileen Tan) two sets each (ARMS & CAUs) were retrieved on 17 July 2025 – 2.5 years after deployment, offering valuable insights into how marine communities have responded to ongoing acidification, warming, and other stressors over a multi-year period. This long-term monitoring is rare in the region and will provide one of the first real-world data sets on how tropical marine life is coping with acidifying seas. The retrieval process involves carefully collecting each structure to analyse colonised organisms, from tiny snails and worms to sessile sponges and bryozoans. This long-term observation is crucial for detecting early signs of biodiversity shifts linked to ocean acidification, particularly among calcifying species such as barnacles, polychaetes, and jewel box clams (Chama spp.). The project examines both mobile organisms (e.g. crabs, worms, shrimp) and sessile organisms (e.g. sponges, bryozoans, Chama bivalves). These often-overlooked species are crucial to reef function and can serve as early indicators of environmental stress. This research could reveal which reef organisms are winners and losers in a changing ocean. Many species found in ARMS are cryptic, meaning they look identical but are genetically distinct. This includes encrusting sponges and bryozoans that blend into the reef structure. DNA barcoding helps researchers detect this hidden biodiversity. The ARMS deployed at Pulau Gaya, Sabah, reveal a distinctly different assemblage of marine organisms compared to those found in the Straits of Malacca. This variation likely reflects the broader biogeographic transition between the Indian Ocean and the Pacific Ocean. Sabah lies within the Coral Triangle and is influenced by Pacific biodiversity, while the Straits of Malacca are more closely aligned with Indian Ocean faunal patterns. The macro-invertebrate community observed here is noticeably different from what we typically see in the Straits of Malacca, featuring species like crinoids, cemented bivalves (Chama sp.), and various types of brittle stars. However, when it comes to cryptic species such as bryozoans and sponges, it is still difficult to distinguish them at this stage. We hope that the upcoming eDNA analysis will provide better resolution and help clarify their diversity. Succession has started with the presence of Chama sp. (Overall, the ARMS looks like already entering later successional phases because of the presence of Chama which is a slow-growing species). Mercs plans to gradually retrieve remaining ARMS units over the next 2.5 years, creating a multi-year time series to understand trends in biodiversity and calcification under changing ocean conditions. Ongoing monitoring is essential to capture the full picture of ocean acidification's impacts, especially as marine conditions continue to shift. Each ARMS unit is like a time capsule of biodiversity, helping researchers track slow but significant changes in the marine ecosystem. Various organisms found on ARMS: Brittle star
Chama bivalve (Jewel box clam)
Six-legged starfish
Crustacean larvae (not identified)
