In the shadow of coral bleaching

Abstract

Coral reefs are highly susceptible to climate change, as evidenced by extensive mass bleaching events over the past decades. Until solutions to reduce greenhouse gas emissions are implemented, pro-active unconventional approaches to conserve local reefs are required. Here, we demonstrate a management strategy aimed at reducing the magnitude of bleaching events over designated reef sections (thousands of square meters). Since high levels of solar irradiance induce coral bleaching, our goal was to technically test the feasibility of shading a shallow reef at the "Japanese Gardens", the highest-value reef in the Eilat Coral Nature Reserve (Israel, Red Sea). In practice, a buoyant shade cloth of 400m2 was deployed on the sea surface over the shallow reef (ca. 6m deep) for a 24-hour period and irradiance, as well as water temperature, were continuously monitored in the shaded and the unshaded reef. The deployment was successful and was completed without causing any physical damage to the reef. In addition to decreasing the irradiance by 85.9% in average, the shade cloth eliminated wave lensing, which produces extremely high irradiance levels and is known to contribute to coral bleaching. Surprisingly, we also found that the water temperature on the shaded reef was up to ca. 0.5oC lower than on the unshaded reef. We propose that the reef shading management strategy can be applied to reefs worldwide and may be particularly valuable on spatially isolated locations. These "islands" of survivors may possibly function as source populations and accelerate the recovery of the destroyed region.