Decline of crinoids on the reefs of Curaçao and Bonaire, Netherlands Antilles

Since 1996 at the latest, comatulid crinoids on the leeward reefs of Curaçao and Bonaire have declined drastically in population size and diversity. Prior to this decline, five species inhabited the forereef slope from depths of 6 to >30 m. Davidaster rubiginosa and an undescribed species of Davidaster were common from about 6 to 15 m depth, and D. discoidea was common below about 15 m. Nemaster grandis and Ctenantedon kinziei were found in lower abundance at about 30 m depth. Transect data from Bonaire showed that a drastic decline in numbers of the Davidaster taxa occurred between 1989 and 1996. Transects in Curaçao in the late 1990s through 2001 documented a similar decline. In 2007, sites in Curaçao where species of Davidaster were formerly common were practically devoid of crinoids. In particular, D. discoidea, once the most numerous crinoid in these islands, has all but disappeared. The cause of this decline on both islands is unknown. It is possible that heating associated with the severe coral bleaching event of 1995 also affected the crinoids. As far as we are aware, reef crinoid populations across the broader western Atlantic region have not shown a similar decline. 

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