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Limited scope for latitudinal extension of reef corals

Science  05 Jun 2015:
Vol. 348, Issue 6239, pp. 1135-1138
DOI: 10.1126/science.1259911

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Not as deep

As our climate warms, many species ranges are predicted to shift toward the warmer poles. Focusing solely on temperatures, however, ignores many factors that change across latitudes, such as the intensity of solar radiation. Muir et al. looked at global distributions of two groups of reef-building corals (see the Perspective by Kleypas). Most reef-building corals occur deep enough to be protected from surge. However, corals require sunlight to sustain their symbiotic photosynthetic algae. Because solar radiation is more limited farther away from the equator, future populations might be limited to more turbulent shallow waters.

Science, this issue p. 1135; see also p. 1086

Abstract

An analysis of present-day global depth distributions of reef-building corals and underlying environmental drivers contradicts a commonly held belief that ocean warming will promote tropical coral expansion into temperate latitudes. Using a global data set of a major group of reef corals, we found that corals were confined to shallower depths at higher latitudes (up to 0.6 meters of predicted shallowing per additional degree of latitude). Latitudinal attenuation of the most important driver of this phenomenon—the dose of photosynthetically available radiation over winter—would severely constrain latitudinal coral range extension in response to ocean warming. Latitudinal gradients in species richness for the group also suggest that higher winter irradiance at depth in low latitudes allowed a deep-water fauna that was not viable at higher latitudes.

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