Coral Reefs in the Anthropocene

Abstract

Although coral reefs cover only 0.00063 of the surface of Earth, they have had important effects on the atmosphere, ocean chemistry, the shape of the surface of Earth, the diversity of life, the biogeographic distribution of life, and they provide hundreds of billions of dollars in value per year in goods and services to tens of millions of humans. All the continents, islands and freshwater habitats of Earth together occupy more than 460 times the total surface area of coral reefs, yet host only 19 phyla while coral reefs host at least 30 phyla of animals. The per square meter value of coral reefs in goods and services has substantially increased since estimated in 1997, but the total value has decreased from loss of coral-reef habitat and stock of large fishes. Coral reef ecosystems in natural undisturbed states can be inverted trophic biomass pyramids with especially high primary production, but meagre yield or net production. Extractive commercial fishing is potentially sustainable if medium-sized individuals and not large individuals are taken. The net yield for human consumption can be increased by removing the upper trophic levels, but the system is more sustainable and beneficial for humans when managed as a service-based economy rather than an extraction-based economy. The present interglacial period (the Anthropocene) has been exceptionally favorable to coral reefs for thousands of years until the recent three or four decades, in which the living coral cover has abruptly declined about 53% in the western Atlantic, about 40% in the general Indo-Pacific, and about 50% on the Great Barrier Reef. Reefs are presently threatened by increasing CO₂. Although there have been few, if any, extinctions, reefs are declining in topographic complexity and ecosystem services. This is most likely the trajectory for future decades and reflects the norm for much of the geologic history of coral reefs.