Updates on corals distribution in Devil’s Crown, Galápagos.

Supervisor: Ken Collins (NOCS, Southampton).
Devil’s Crown (Corona del Diablo) is a submerged volcanic caldera with an emergent basalt rim located in the southern Galápagos Islands, Ecuador. In the past, snorkelers were attracted to Devil’s Crown’s appealing setting in an extinct caldera, its dominant pocilloporoid coral community and its high variety of small invertebrates and fishes that did not occur on the adjacent sandy substrates (Feingold, 1995; 1996). However, rapid and sharp changes in sea surface temperature and storms associated to strong El Niño/Southern Oscillation (ENSO) events, followed by intensive sea urchins Eucidaris bioerosion have resulted in great mortality of the coral communities and the access to Devil’s Crown has been closed to the tourism. Glynn & Wellington (1983) and Glynn (1994) studies are some of the few sources on coral distribution in Devil’s Crown. The aim of this study was to map current coral distribution in Devil’s Crown and compare with previous published maps, under the hypothesis that changes have happened over the past 40 years. For achieving this goal, videos recorded by snorkeling/scuba-diving were used to assess coral distribution and build a 2018 map. Previous published maps of Devil’s Crown corals communities in 1976, 1985 and 1993 were digitalized, georeferenced and compared with the 2018 map. Pavona/Porites is the only coral community which recovery to 1976 levels was statistically confirmed in this study, although this population had significant decrease between 1985-1993. There are strong indications of recovery of Psammocora colonies (photographic evidences, areas estimated by ArcGIS) since their apparent disappearance in 1985 and 1993, however this recovery was not statistically confirmed. The previous dominant and centrally positioned Pocillopora population, now it is restricted to a few colonies in the northeastern part of Devil’s Crown and presents the lowest percentage between the six major categories analyzed (Pavona/Porites;Psammocora, Megabalanus/rock, sand, bed rock/coral rubble). Megabalanus/rock area cover increased substantially post 1982-1983 ENSO event and remained high, but with no significant increase after 1985. The presence of sea urchin Eucidaris population is still prevalent in Devil’s Crown, but only a few of them were found grazing living coral, usually Pavona/Porites. The majority of Pavona/Porites presented scars of fish bites and signs of mollusc bores. A few colonies of Pavona/Porites were found with a pinkish discoloration on the surface, an indication of disease or mechanical/chemical disturbance. It is expected that the updated coverage of the corals distribution, the images and the georeferenced maps from this study will inform marine reserve managers and provide data for a future monitoring baseline.