Are deep sea reefs really a lifeboat for our vanishing corals?

Date: November 7, 2018

Source: Mongabay
Author: Emily Clark

When Luiz Rocha, a fish biologist at the California Academy of Sciences, goes scuba diving, he tacks on one and a half times his body weight in specialized diving gear. Once he submerges, he can’t spare a moment to take in the vibrant corals just beneath the surface — he has greater depths to plumb.

Rocha is headed toward what Smithsonian Institution fish biologist Carole Baldwin calls “a very diverse and productive portion of the tropical ocean that science has largely missed”: mesophotic reefs. “Mesophotic” is Greek for “middle light,” referring to the intermediate amount of sunlight that can penetrate to depths of 30 to 150 meters (100 to 500 feet) below the ocean’s surface.

The dives required to reach mesophotic reefs are as technical as they are deep. Strapped to a larger-than-average gas tank, Rocha uses the rebreather method, recycling the air he breathes as he goes.

The coral species from shallower reef communities begin to taper off around 30 meters into Rocha’s dive. At 100 meters (330 feet), the water chills significantly. This is the thermocline, defined by the National Oceanic and Atmospheric Administration (NOAA) as the transition layer between the sunlight-warmed water at the surface, and the colder water below.

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