A key consideration in assessing impacts of climate change is the possibility of synergistic effects with other human-induced stressors. In the ocean realm, climate change and overfishing pose two of the greatest challenges to the structure and functioning of marine ecosystems. In eastern Tasmania, temperate coastal waters are warming at approximately four times the global ocean warming average, representing the fastest rate of warming in the Southern Hemisphere. This has driven range extension of the ecologically important long-spined sea urchin (Centrostephanus rodgersii), which has now commenced catastrophic overgrazing of productive Tasmanian kelp beds leading to loss of biodiversity and important rocky reef ecosystem services. Coincident with the overgrazing is heavy fishing of reef-based predators including the spiny lobster Jasus edwardsii. By conducting experiments inside and outside Marine Protected Areas we show that fishing, by removing large predatory lobsters, has reduced the resilience of kelp beds against the climate-driven threat of the sea urchin and thus increased risk of catastrophic shift to widespread sea urchin barrens. This shows that interactions between multiple humaninduced stressors can exacerbate nonlinear responses of ecosystems to climate change and limit the adaptive capacity of these systems. Management actions focused on reducing the risk of catastrophic phase shift in ecosystems are particularly urgent in the face of ongoing warming and unprecedented levels of predator removal from the world’s oceans.
Marine protected areas (established 12 and 31 years before experiment for the two different sites respectively)
|Climate change impacts||Effect of Nbs on CCI||Effect measures|
|Increased pests||Positive||Survivorship of Centrostephanus rodgersii (pest)|
The Maria Island Marine Reserve (MIMR, 42° 35.26 S, 148° 3.03 E) and the Crayfish Point Research Reserve (CPRR, 42° 57.37 S, 147° 21.30 E) (the intervention sites) and adjacent fished sites (the control sites)