Elevated sea surface temperatures associated with El Niño-Southern Oscillation (ENSO) can severely impact coral populations in the Galápagos Islands, Ecuador. During the 1982-83 event, 95-99% of reef-building corals bleached and died. This study examines if the onset of the 2015-2016 ENSO affected the important reef-building coral Pocillopora damicornis. The largest known population of this species in the Archipelago is found in the Concha de Perla lagoon on the southern coast of Isabela Island. Asexual reproduction via fragmentation is an important mode of population maintenance and growth in this species. Consequently, there is often low genetic variability in local populations. However, surprisingly, this population comprises a single genet. It was first surveyed in 2012 and was visited again in 2015 to determine if colony size and coral condition (bleaching, paling, or mortality) changed. Underwater photographs were quantified for these attributes using the Coral Point Count with Excel Extensions (CPCe) program. In 2012 nearly the entire population (1,617 colonies) was surveyed and compared to a smaller, haphazard survey (370 colonies) performed in 2015.
Results/Conclusions
There was a significant increase in live mean colony size from 2012 (249.8 ± 305.3) to 2015 (327.8 ± 257.4), (p < 0.001, t-Test), suggesting that colony growth is occurring. Live colony sizes were skewed right in both surveys, typical of coral population structure for most species. However, the mode shifted from the smallest size classes (0-100 cm2) in 2012 to slightly larger size classes (100-150 cm2) in 2015. This indicates that colonies grew in size, but there was a reduction in new recruits, suggesting a decline in successful asexual reproduction. In 2012, 263 fragments were observed associated with 1,617 colonies (16.3%), compared to 29 fragments associated with 370 colonies (7.8%) in 2015. Coral bleaching and paling were not observed, however positive sea surface temperature anomalies had not persisted for long, and impacts may yet occur. Because this population is monoclonal with no genetic variability, it is more susceptible to the types of environmental change associated with ENSO. Its proximity to the population center of Puerto Villamil on Isabela Island gives this ecological oasis high touristic appeal and consequently high economic value. Continued monitoring of this persistent population is warranted.