Are all seagrasses created equal? Quantifying the relative value of ecosystem services on the Great Barrier Reef

Seagrasses are recognized as one of the most productive ecosystems on earth. They provide a wide array of ecosystem services including particle trapping that improves water quality, stabilization of sediments, provision of... [ view full abstract ]

Seagrasses are recognized as one of the most productive ecosystems on earth. They provide a wide array of ecosystem services including particle trapping that improves water quality, stabilization of sediments, provision of food for dugong and turtles, carbon sequestration, and the creation of habitat for animals thereby facilitating biodiversity. Alarmingly, however, global coverage of seagrass ecosystems is declining rapidly, with habitat loss estimated at 110 sq. km / year and accelerating. Approximately 30% of the world’s seagrasses have disappeared since World War II. In response, seagrass habitats in Australia have been protected through legislative efforts. The Great Barrier Reef (GBR) contains approximately 35,000 sq. km of seagrass representing 6-12% of the world’s known seagrass area. Within the GBR 90% of seagrasses are found in deep-water (>15 m) habitats, placing them among the most extensive populations on Earth. At present, information is lacking on how the ecosystem services provided by seagrasses growing in deep-water environments compare to those documented in shallow habitats. Deep-water seagrasses on the GBR are characterised by ephemeral or seasonal populations dominated by sparse coverage of low biomass Halophila species and may not provide the same level of services as the more permanent, densely populated multi-species meadows that are characteristic of shallow water habitats. This presentation combines data from recent surveys of carbon storage capacity in deep versus shallow water meadows in the GBR with a review of the capacity of the two habitats to contribute to other major ecosystem services to make the case that deep-water seagrasses are not as "valuable" as their shallow water counterparts. Estimating the relative magnitude of the contributions of ecosystem services in different seagrass habitats will provide the best result for protecting and managing these important natural resources.