Field Guide to Select Eastern Pacific Corals and Associated Coral Reef Biota

Abstract

Bioerosion, the weakening and erosion of hard substrates by boring, etching, and grazingorganisms, is a major structuring force on coral reefs of the Eastern Tropical Pacific (ETP).Bioerosional processes are the main source of reef erosion, and facilitate recycling of reefalcarbonate. In healthy reefs, a dynamic balance exists between destructive (i.e. bioerosion)and constructive (i.e. bioaccretion) processes, allowing for maintenance and growth of reefframeworks. In changing environments, however, bioerosion rates can exceed those ofcoral calcification, leading to reduced reef development and the destruction of reefframeworks. In the ETP, high rates of bioerosion are promoted by nutrient-rich upwellingand high primary productivity conditions, recurrent coral bleaching and mortality events,and a chemical environment characterized by high-pCO2and low aragonite saturation state.Here we examine bioerosion in ETP coral habitats and the variable roles of reef-dwellingbioeroder taxa: microbial euendoliths (microendoliths), sponges, polychaetes, sipunculans,crustaceans, molluscs, echinoids, and reeffishes. Among these agents of bioerosion,sponges, sipunculans, bivalves, and echinoderms have been relatively well studied in this region, while information is currently lacking or limited for microendolith assemblages,polychaetes and reeffishes. The frequency of coral invasion by clionaid sponges (e.g.,Cliona vermiferaandThoosa mismalolli) is variable between ETP coral habitats. Denseboring sponge assemblages can lead to high rates of carbonate losses exceeding those ofbioaccretion. Boring bivalves (i.e., species ofLithophagaandGastrochaena) are veryabundant on many actively accreting reefs and are generally more prominent contributors toreef erosion in the ETP than in other regions. Sea urchins are by far the most destructivegrazers of coral substrates in habitats where abundant. Following ENSO-associated coralmortality events, intense bioerosion by sea urchins has impeded coral recovery andcompromised reef health at many eastern Pacific sites. This chapter reviews factorsimportant in ETP bioerosion, and current knowledge of bioeroder populations in the region.