Torres Strait Eastern Cluster: intertidal seagrass baseline survey

This report describes a baseline survey of reef-top and island intertidal benthic habitats, including seagrass, algae and coral, in the Eastern Cluster of the Torres Strait. The Central Cluster’s Masig Island was included in the survey due to the island’s ecological links with the Eastern Cluster. Torres Strait contains extensive seagrass habitat, the largest dugong population in the world, and globally significant populations of green turtles. Dugong feed exclusively on seagrass while green turtles consume seagrass and algae. Torres Strait’s Eastern Cluster is an ecologically important region in the traditional land and sea country of the Kemer Kemer Meriam Nation. The area is a potential thermal refuge for coral reefs and contains the most important green turtle rookeries in Torres Strait for the northern Great Barrier Reef population. 2575 + 323 hectares of intertidal seagrass was mapped across 24 intertidal meadows in September 2020. Large seagrass meadows occurred on fringing reefs around the inhabited islands of Erub (Darnley), Masig (Yorke) and Mer (Murray). Smaller high biomass meadows surround Waier and Dauar Islands. Patchy, low biomass meadows occurred on reef-tops close to Erub Island and at Maizub Kaur (Bramble Cay). Seagrass species diversity was greatest at meadows surrounding the largest continental islands of Mer and Erub and the heavily vegetated cay of Masig Island. Six seagrass species were recorded, but meadows were dominated by two common reef-associated species Thalassia hemprichii and Cymodocea rotundata. Intertidal reefs and islands also contained extensive algae habitat and coral communities. Hard coral cover was as high as 100% at some survey sites. The presence of meadows in similar areas to surveys conducted >10 years prior, and the dominance of the persistent reef-top species T. hemprichii, indicates the Masig Island and the Eastern Cluster’s intertidal meadows provide a relatively stable foraging ground for marine herbivores. Seagrass information presented in this report and available on eAtlas can be used to inform the Erubam Le, Keriba Luzabzab-Lera Dorge and Masigalgal Dugong and Turtle Management Plans. Assessing and managing the health of Torres Strait seagrass and other benthic habitats requires the collection of baseline information plus ongoing monitoring to understand longterm variation and detect seagrass decline. We recommend the establishment of long-term, meadow-scale monitoring at Masig, Mer and Erub Islands. We also recommend expanding baseline surveys to include Ugar (Stephens Island) as data there is >10 years old