[A-CG41] Coastal Ecosystems -2. Coral reefs, seagrass and macroalgal beds, and mangroves

[ACG41-10] Degraded turf algal systems are ‘locked-in’ by ocean acidification

*Benjamin Paul Harvey¹, Ro Allen^2,3, Sylvain Agostini¹, Linn J Hoffmann², Koetsu Kon¹, Tina C Summerfield², Shigeki Wada¹, Jason M Hall-Spencer^1,4 (1.Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka 415-0025, Japan, 2.Department of Botany, University of Otago, Dunedin, New Zealand, 3.The Marine Biological Association, Plymouth, Devon PL1 2PB, UK, 4.School of Biological and Marine Sciences, University of Plymouth, Plymouth PL4 8AA, UK)

Keywords:Regime Shifts, Feedback Loops, Hysteresis, CO2 Seeps, Turf Algae

Human activities are rapidly changing the structure and function of coastal marine ecosystems. Large-scale replacement of kelp forests and coral reefs with turf algal mats is resulting in homogenous habitats that have less ecological and human value. Ocean acidification has strong potential to substantially favour turf algae growth, which led us to examine the mechanisms that stabilise turf algal states. Here we show that ocean acidification promotes turf algae over corals and macroalgae, mediating new habitat conditions that create stabilising feedback loops (altered physicochemical environment and microbial community, and an inhibition of recruitment) capable of locking turf systems in place. Such feedbacks help explain why degraded coastal habitats persist after being initially pushed past the tipping point by global and local anthropogenic stressors. An understanding of the mechanisms that stabilise degraded coastal habitats can be incorporated into adaptive management to better protect the contribution of coastal systems to human wellbeing.