Chris T. Perry & Lorenzo Alvarez-Filip
The ecosystem goods and services that coral reefs provide largely depend on the capacity of reef ecology to sustain key geo-ecological functions, including the maintenance of reef structural complexity, reef growth potential and sediment generation. These functions depend on the rates at which reef species produce carbonate – skeletal material deposited by corals and other calcifying species – and the rates at which other taxa, such as parrotfish, urchins, sponges and microendolithic organisms, erode those carbonate structures or convert them to sediment. The balance between these constructional and erosional processes largely determines the geo-ecological functioning of coral reefs.
As local and global pressures increase, the capacity of reefs to sustain these geo-ecological functions is likely to be increasingly impaired. Thus, although the Anthropocene footprint of reef disturbance will be expressed differently across eco-regions and habitats, the end point for many reefs may be broadly similar. Specifically, many reefs will progressively shift towards net neutral or negative carbonate budget states, will become structurally flatter, and will having lower vertical growth rates. The net consequence of these changes is that the Anthropocene is likely to be defined by an increasing disconnect between the ecological processes that drive carbonate production on the reef surface, and the net geological outcome of that production (the accumulation of the underlying reef structure).
Whilst there is evidence of some reefs recovering from short-lived disturbances, such as climate-driven coral bleaching, the frequency and intensity of these events is predicted to increase. This would increase the spatial footprint of disturbances and reduce the capacity of important reef-building corals to recover and sustain positive carbonate budgets. Reef structures are thus likely, in many areas, to become increasingly relict features, defined by low habitat complexity, low growth rates and low sediment production regimes. Whilst geographic isolation or the presence of favourable (refugia) environmental conditions may buffer some reefs from these negative trajectories, the enforcement of effective marine protection alongside rapid actions on CO2 emissions will be required if more optimistic futures are to be envisaged over large geographic areas.