A New Baseline for Diadema antillarum, Echinometra viridis, E. lucunter, and Eucidaris tribuloides Populations Within the Cayos Cochinos MPA, Honduras

Abstract

AbstrAct: We investigated the density of 4 urchin species from 5 shallow reefs in the Cayos Cochinos Marine Protected Area in Honduras. Individual species density varied among reefs with total urchin density ranging from 3.2–7.9 individuals/m 2 . Echinometra viridis (Agassiz, 1863) was the numerically dominant species (2.29/m 2) followed by E. lucunter (Linnaeus, 1758) (1.76/m 2) with Eucidaris tribuloides (La-marck 1816) representing the fewest individuals (0.42/m 2). Our results indicated that density of Diadema antillarum (Philippi, 1845) differed significantly among reefs (0.4—1.3/m 2 , mean = 0.63/m 2), but are three times greater than data collected 12 years after the mass mortality event of the1980's. Size frequency analysis of D. antillarum indicated that test diameter also differed significantly among reef sites while cor-relation analysis showed that D. antillarum density was negatively related to both coral and algal cover. Echinometra viridis density, however, was positively related to coral cover (p < 0.05). When all urchins were combined, they showed a negative correlation with algal cover and a positive correlation with coral cover indicating a potential top—down effect within the reefs. While urchin densities remain relatively low compared to other sites in the Caribbean, the D. antillarum population appears to be recovering in this Honduran MPA. If overall grazer abundance continues to increase then they may limit macroalgae on reefs, thereby encouraging coral settlement.