Assessment of current rates of Diadema antillarum larval settlement

The generally slow and incomplete recovery of the long-spined sea urchin, Diadema antillarum, from the 1983–84 Caribbean-wide die-off, particularly in the Florida Keys, USA, raises the question of factors limiting population recovery. This study sought to quantify larval settlement rates as an indicator of larval supply at two sites in the Florida Keys, utilizing methods comparable to an historic study. Settlement at two sites in southwest Puerto Rico was also examined as a comparison of present-day settlement rates at a site where D. antillarum recovery has been moderate. Monthly settlement rates were low (max < 2 m−2) and did not differ between the two sites examined in the Florida Keys. Settlement was significantly higher at only one of the Puerto Rico sites (max 16 m−2), but still an order of magnitude lower than that reported for historic populations in Curaçao (1982–83). Results are consistent with the hypothesis of low larval supply limiting D. antillarum recovery in the Florida Keys.