Beyond the tropics: ocean warming, shifts in species interactions and the tropicalisation of temperate reefs

Adriana Vergés (1), Hamish Malcolm (2)

1 UNSW Australia, School of BEES, NSW 2052, Australia,, @adriatix

2 NSW Department of Primary Industries, Coffs Harbour NSW 2450, Australia,

Climate-driven changes in species interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in plant-herbivore interactions can lead to the loss of dominant habitat forming species such as corals when tropical fish herbivory decreases, or to declines in algal forests when temperate urchin grazing increases. Emerging evidence from Japan and eastern Australia indicates that ocean warming is causing a novel type of phase-shift in tropical-temperate transition zones, whereby tropical and subtropical herbivores are overgrazing the canopy forming algae that typically dominates shallow temperate reefs. In eastern Australia, we use a ten-year (2002-2012) video dataset that encompassed a 0.6°C increase in mean sea surface to quantify patterns of kelp-herbivore interactions in a tropical-temperate transition zone. Kelp was present on 70% of surveyed reefs in 2002, declined through time and completely disappeared from 2010 onwards. Simultaneously, grazing incidence on kelp increased steadily from <10% to over 70% in the years preceding kelp disappearance. The proportion of tropical and herbivorous species in fish communities increased as kelp declined. Experimental video evidence shows transplanted kelp is quickly consumed within hours by tropical rabbitfish (Siganidae) and drummers (Kyphosidae) in reefs from where it has disappeared, where large densities of grazing surgeonfish dominate consumption of algal turfs. Our results suggest that climate-mediated increases in herbivory pose a very significant global threat to kelp dominated ecosystems and the communities they support.

Species on the Move

An International Conference Series

The conference brings together scientists and natural resource managers working in the disciplines of global change, biogeography and evolution, and relevant in contexts of natural resource management, biodiversity management and conservation, and theoretical ecology.

Species responses to climate change is a rapidly evolving research field, however, much of our progress is being made in independent research areas: e.g. understanding the process vs responding to the implications, terrestrial vs marine ecosystems, global meta-analyses vs in depth species-specific approaches. This interdisciplinary conference develops connections between these parallel streams, and across temporal and spatial scales.

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