Experimental dispersal of recovering Diadema antillarum increases grazing intensity and reduces macroalgal abundance on a coral reef

Abstract

The 1983 mass mortality of the sea urchin Diadema antillarum greatly decreased grazing intensity on Caribbean reefs, contributing to widespread increases in algal abundance and exacerbating decreases in coral cover. Urchin populations have been recovering in some areas, most notably the reefs of Jamaica's north coast. We manipulated the density of D. antillarum in the buttress zone of a previously unstudied Jamaican reef where the recovering urchins have a clumped distribution. Some buttresses have a large number of urchins while others nearby have none. We transplanted half of the urchins from high urchin density donor buttresses to low urchin density recipient buttresses. Transplantation significantly decreased the percent cover of macroalgae and increased the amount of bare space. These changes occurred despite a generally low retention of transferred urchins on recipient buttresses. Those urchins remaining on the recipient buttresses aggregated at rugose locations around which algae-free barrens appeared. Transplantation of urchins decreased their local density while maintaining overall density on the reef. The increase in algal consumption after transplantation implies that aggregated urchins compete for algae. Whereas aggregated D. antillarum tend to graze within the same area and have only a localized effect on algae, dispersed urchins compete less and eat more. Increased bare space could enhance recruitment of corals, further improving reef health. Our methods could potentially be used as an inexpensive reef restoration tool. Such restoration projects would be most effective if recipient sites with natural or artificially increased rugosity are used.

Topography and spatial arrangement of reef-building corals on the fringing reefs of North Jamaica may influence their response to disturbance from bleaching

“…Hawaii (Howard et al, 2009), the Great Barrier Reef (Emslie et al, 2008), Barbados (Chapman and Kramer, 1999), the Seychelles (Wilson et al, 2007), and the Gulf of Mexico (Rooker et al, 1997). Rugose locations aid aggregation of Diadema antillarum urchins, important to keep macroalgae in check (Macia et al, 2007).…”

Coral Reef Populations in the Caribbean: Is There a Case for Better Protection against Climate Change?

“…34,35]. However, some studies have highlighted continued climatic and other impacts in regions of MPAs [36][37][38].…”

Coral responses to macroalgal reduction and fisheries closure on Caribbean patch reefs

“…Various experimental manipulations, such as removing algae, ad ding the sea urchin Diadema antillarum, and fisheries management have failed to return these patch reefs to coral dominance (McClanahan et al 2001). Adding sea urchins can assist in reducing algae, but they can also quickly decline within days after additions (Maciá et al 2007, T. R. McClanahan pers. obs.).…”

“…Experimental efforts to reduce algae in order to promote coral recovery found that algae return quickly, within 6 mo, and this is not sufficient time to facilitate coral recovery (McClanahan et al 2001). There is some evidence that the recovery of herbivorous sea urchins and fishes facilitate coral recovery, but these changes have often been small or on a small spatial scale (Carpenter & Edmunds 2006, Mumby et al 2006, Maciá et al 2007, Idjadi et al 2010. Fisheries closures have been promoted as a way to increase herbivorous fish abundances, creating high grazing conditions required of corals.…”