Predicting seagrass recovery times and their implications following an extreme climate event

Extreme temperature events are predicted to become more frequent and intense as climate change continues, with important implications for ecosystems. Accordingly, there has been growing interest in what drives resilience to climatic disturbances. When a disturbance overwhelms the resistance of an ecosystem, it becomes vulnerable during recovery, with implications for ecosystem function and persistence. Understanding what influences ecosystem recovery is particularly important in seagrass ecosystems because of their functional roles, vulnerability, and divergent recovery strategies. Seagrass cover was monitored for 3 yr following a large, heatwaveassociated mortality event in Shark Bay, Australia. Although the ecosystem's historically dominant foundational seagrass, Amphibolis antarctica, is capable of rapid disturbance recovery, this did not occur, likely because of the failure of mechanisms which have driven rapid recovery in other systems (persistence of rhizome beds, sexual reproduction among neighboring beds). Instead, a tropical early successional seagrass, Halodule uninervis, became more common, increasing diversity. These changes in the structure of the Shark Bay seagrass ecosystem, and reduction of biomass and structural complexity, will have important implications for ecosystem services and community dynamics and indicates that this ecosystem is highly vulnerable to future disturbances. More generally, our work suggests that seagrass ecosystems typified by a mix of early and late successional species may be particularly likely to exhibit a mismatch between recovery of cover per se and recovery of function following disturbance. As such, extreme climatic events have the potential to abruptly alter seagrass community dynamics and ecosystem services.