Thin cylindrical branches that grew in dense thickets in mid-depth water. It declined with the elkhorn and for the same reasons, and most of what is seen now is in restoration plots.
Thickets exceeding 2 m in both height and width, with branches roughly 2.5 to 7.5 cm thick. Open antler-like branching with cylindrical branches tapering to blunt tips, and at the tip of each branch a distinct tubular cup surrounded by smaller ones. Light brown, beige or tan, sometimes green, blue or purple, with the branch tips typically paler or white.
Elkhorn coral has flattened blade-like branches rather than round ones. Between the two sits a naturally occurring hybrid of the two species, which is intermediate and bushy with somewhat flattened branches and is genuinely ambiguous.
It is the fastest-growing Caribbean reef coral, adding up to five centimetres of new skeleton per centimetre of existing skeleton per year, and it historically built the back-reef and fore-reef thickets. It spreads mostly by fragments breaking off and regrowing, which is why it is the workhorse of coral nurseries and restoration. It is most common in the top 20 m of clear water.
It is critically endangered and was one of the first two corals listed under the US Endangered Species Act, in 2006. The collapse was caused by white-band disease, first seen in 1979, which accounts for as much as 95 per cent of the decline. That is a different disease from the stony coral tissue loss disease that has emptied Florida reefs since 2016, which largely spares this family. The two should not be run together.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
