Black Band Spread (image) Max-Planck-Gesellschaft Caption The dark front of the BBD migrates towards the healthy tissue and leaves the bare coral skeleton behind. Sulfidic (+H2S) and anoxic (-O2) conditions are responsible for the necrosis of the coral tissue in the BBD zone. Credit M. Glas/R. Dunker Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.