Experimental effects of sediment burial and light attenuation on two coralline algae of a deep water rhodolith bed in Rio de Janeiro, Brazil

A dense rhodolith bed on deep-water soft bottoms in the Peregrino oil field in Campos Basin, Brazil was recently described. This critical habitat is increasingly subjected to disturbances that promote massive sediment dislodgment. This study aimed to test the combined effects of sediment burial and light attenuation on two main rhodolith-forming coralline algae. Experiments were conducted using the dominant algae Mesophyllum engelhartii and Lithothamnion sp. Color changes were measured as a response to burial with a thin layer of fine and coarse sediments compared to uncovered samples at two natural light levels. A mesocosm system exposed species to combined treatments of light and burial by sediments that mimic drill cuttings. M. engelhartii bleached after 75 days and Lithothamnion sp. earlier than that, at 41 days, when buried by fine sediments. Sediments had a strong negative effect on the photosynthesis of coralline algae species within two weeks. Low light levels are not a problem for these deep-water coralline species, but fine sediments have a negative effect after a relatively short time. Lithothamnion was more sensitive than M. engelhartii in terms of color changes but less sensitive in terms of their fluorescence responses to burial.