Impact of Marine Heatwaves on Seagrass Ecosystems

Abstract

Seagrass meadows deliver important ecosystem services such as nutrient cycling,enhanced biodiversity, and contribution to climate change mitigation and adap-tion through carbon sequestration and coastal protection. Seagrasses, however,are facing the impacts of ocean warming and marine heatwaves, which are altering their ecological structure and function. Shifts in species composition,mass mortality events, and loss of ecosystem complexity after sudden extremeclimate events are increasingly common, weakening the ecosystem services theyprovide. In the west coast of Australia, Shark Bay holds between 0.7 and 2.4% ofglobal seagrass extent (>4300 km2), but in the austral summer of 2010/2011, theNingaloo El Niño marine heatwave resulted in the collapse of ~1300 km2ofseagrass ecosystem extent. The loss of the seagrass canopy resulted in the erosionand the likely remineralization of ancient carbon stocks into 2–4TgCO2-eqover6 years following seagrass loss, increasing emissions from land-use change inAustralia by 4–8% per annum. Seagrass collapse at Shark Bay also impactedmarine food webs, including dugongs, dolphins, cormorants,fish communities,and invertebrates. With increasing recurrence and intensity of marine heatwaves,seagrass resilience is being compromised, underlining the need to implementconservation strategies. Such strategies must precede irreversible climate change-driven tipping points in ecosystem functioning and collapse and result fromsynchronized efforts involving science, policy, and stakeholders. Managementshould aim to maintain or enhance the resilience of seagrasses, and using propa-gation material from heatwave-resistant meadows to restore impacted regionsarises as a challenging but promising solution against climate change threats.Although scientific evidence points to severe impacts of extreme climate eventson seagrass ecosystems, the occurrence of seagrass assemblages across the planetand the capacity of humans to modify the environment sheds some light on thecapability of seagrasses to adapt to changing ecological niches.