Spatial variation in sea urchins, fish predators, and bioerosion rates on coral reefs of Belize

摘要

Although sea urchins are critical for controlling macroalgae on heavily fished coral reefs, high densities threaten reefs, as urchins are also prodigous bioeroders. This study examined urchin population characteristics, bioerosion rates, their fish predators (Labridae), and potential competitors (Scaridae) on unprotected reefs and a reef within a marine protected area (MPA) in the lagoonal regions off Belize. Urchin density (<1 m?2) and bioerosion rates (～0.2 kg CaCO3 m?2 year?1) were lowest and members of the Labridae were the highest (～20 fish 200 m?3) within the MPA, while several unprotected reefs had higher (～18–40 m?2) urchin densities, lower Labridae abundances (1–3 fish 200 m?3), and bioerosion rates ranging from ～0.3–2.6 kg CaCO3 m?2 year?1. Urchin abundances were inversely related to Labridae (wrasses and hogfish) densities; however, on reef ridges, low algal cover (～15%), small urchin size (～14 mm), and low proportion of organic material in urchin guts suggested food limitation. Both top–down (predation) and bottom–up factors (food limitation) likely contribute to the control of urchins, predominantly Echinometra viridis, off Belize, thereby potentially diminishing the negative impacts of bioerosion activities by urchins.