Crinoid paradox
The status of coral reefs around the world is almost exclusively gauged by data on reef-building corals (live coverage, diversity, prevalence of diseases or bleaching), macroalgae (coverage, diversity), and fish (diversity, abundance). Long-term monitoring data on the myriad of other reef biota are quite scarce. Exceptions are population density of the echinoderms Diadema antillarum or Acanthaster planci, or the Queen Conch, Lobatus gigas. In most cases, as we are well aware, long-term trends in population density are declining. Gradual long-term or drastic increases are well known for macroalgae, lionfish or A. planci. Here I am calling attention to changes in population density of reef- dwelling comatulid crinoids (“feather stars”, Echinodermata) on some western Atlantic reefs in Jamaica and the Netherlands Antilles, that are paradoxical as they are counter to long-term trends in the better-known indicators of coral coverage and fish abundance.