Between 1985 and 2012, the area of Australia’s Great Barrier Reef covered by coral declined by about 50%. Three processes drove the observed decline: physical destruction by tropical cyclones, predation by Crown-of-Thorns Sea Stars, and bleaching. Over the same interval, reefs in the Caribbean Sea similarly declined at a rate of about 1.5% per year, mostly because of storms, disease, bleaching, and the spread of algae due to overexploitation of fish that keep algal populations in check.

The declining health, areal extent, and diversity of coral reefs reflect some of the same factors that challenge biodiversity in general: overexploitation of associated species and habitat alteration due to fertilizer runoff. Outbreaks of Crown-of-Thorns Sea Stars may reflect both the overexploitation of predators on the sea stars and increased nutrient influx that appears to increase the survival of sea star larvae. Increased storm frequency and intensity, as well as bleaching, reflect another factor—climate change. Human activities such as agriculture and fishing will continue into the future, but warming temperatures and ocean acidification are becoming increasingly important threats to reefs in coming decades. This shouldn’t deter us from addressing threats to reef ecosystems from local disturbances, but underscore the probability that reef conservation and management will require strategies to mitigate the effects of global change, as well.

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The same is true on land. It is necessary and important to maintain reserves that protect natural habitats and the species they support, but, on the timescale of the next century, the climate of protected areas will change, and with it the capacity of the reserve to support its native biodiversity. Under these conditions, corridors will play a particularly important role in enabling populations to move from one reserve to another with local climate more amenable for growth and reproduction. Many ecologists think that natural corridors to promote migration will not be sufficient—that conservation biologists will need to implement a carefully considered program of assisted migration to match populations with appropriate environments.

In southern Africa, conservation efforts have benefited substantially by grouping reserves across national borders and connecting them with corridors. For example, a broad conservation area now links national parks and other reserves in South Africa, Mozambique, and Zimbabwe, providing an enlarged area for conservation corridors that connect established reserves and permit seasonal migration (Fig. 49.26). A key point is that, within this conservation area, animals and people coexist. Many corridors, in Africa and elsewhere, necessarily pass through populated areas, so local support is essential. In southern Africa, people within the conservation area have been persuaded that the preservation of biodiversity is in their best economic interests.