Deep-Sea News

Discovery of Deep-water Seagrass in Pristine Indian Ocean

Research led by the Swansea University's Bioscience department, UK, has discovered for the first-time extensive deep-water seagrass meadows in the middle of the vast Indian Ocean through satellite tracking the movement of green sea turtles.

The new study, done in collaboration with Deakin University academics, published in the recent Marine Pollution Bulletin, reporting how the monitoring of the turtles -- which forage on seagrasses -- tracked the species to the Great Chagos Bank, the world's largest contiguous atoll structure in the Western Indian Ocean.

By using in-situ SCUBA and baited video surveys, the researchers investigated the day-time sites occupied by the turtles, resulting in the discovery of extensive monospecific seagrass meadows of Thalassondendron ciliatum. Seagrass was first reported to exist in this area – which lies in the heart of one of the world's largest Marine Protected Areas (MPAs) - anecdotally during a 2010 SCUBA based expedition.

EMBED 1 extensiveseaGreen turtle with seagrass in the Caribbean. Credit: Swansea University

Dr Nicole Esteban, a Research Fellow at Swansea University's Biosciences department, said, "Our study demonstrates how tracking marine megafauna can play a useful role to help identify previously unknown seagrass habitat. We hope to identify further areas of critical seagrass habitat in the Indian Ocean with forthcoming turtle satellite tracking research."

These habitats are critically important for storing huge amounts of carbon in their sediments and for supporting fish populations. At three sites that extended over 128km of the Great Chagos Bank, there was a high seagrass cover (average of 74%) at depths to 29 meters. The mean species richness of fish in the seagrass meadows was 11 species per site, with a mean average across all sites of 8-14 species.

Results showed a high fish abundance as well as a large predatory shark recorded at the three sites. Given that the Great Chagos Bank extends over approximately 12,500km and many other large deep submerged banks exist across the world's oceans, the results suggest that deep-water seagrass may be far more abundant than previously suspected. Reports of seagrass meadows at these depths with high fish diversity, dominated by large top predators, are relatively limited.

Dr Richard Unsworth, from Swansea University's Biosciences department, said "Seagrasses struggle to live in deep waters due to their need for high levels of light, but in these crystal-clear waters of Chagos these habitats are booming. Given how these habitats are threatened around the world it's great to come across a pristine example of what seagrass meadows should look like."


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