Effects of irradiance, flow, and colony pigmentation on the temperature microenvironment around corals: Implications for coral bleaching?

Abstract

Experiments were conducted to determine the effects of colony pigmentation, irradiance, and flow on the temperature microenvironment that corals experience in shallow water. The warming of colony surfaces increased with increasing colony pigmentation (darker surfaces) and at high irradiance but was alleviated by higher water flow. Dark colonies were up to 1.5°C warmer than ambient seawater at high irradiance and slow flow. In contrast, very light colonies were similar in temperature to ambient water at all levels of flow and irradiance. The darkness of corals progressively increased along a gradient of decreasing water clarity from oligotrophic offshore reefs toward turbid high-nutrient reefs near the coast. The surface temperature of these darkly pigmented turbid-water corals was significantly greater than that of the paler corals in the clear-water environments at comparable seawater temperatures, light, and current conditions. The surface warming of darkly pigmented colonies in coastal environments is sufficiently high to exceed their bleaching threshold during warm, calm, and clear seawater conditions. © 2006, by the American Society of Limnology and Oceanography, Inc.