Black coral

Despite the name, living black coral appears dark green or brown due to a thin layer of polyp tissue covering the dark internal skeleton. The branching tree-like colonies on the Bookends walls grow extremely slowly — some specimens may be over 70 years old — and serve as microhabitats for longnose hawkfish, decorator crabs, and cryptic commensal shrimp. Black coral is protected under CITES Appendix II; its historical collection for jewellery has devastated populations at shallower Caribbean sites.