Population Fluctuation of the Nodular Coral Psammocora stellata in the Galápagos Islands, Ecuador: An Indicator of Community Resilience and Implications for Future Management

Corals are experiencing a worldwide decline in abundance and diversity. Reasons for this include anthropogenic impacts and associated changes to environmental conditions, including global climate change. Increasing atmospheric CO2 levels lead to a coordinated increase in sea surface temperatures and decrease in oceanic pH. Warming events associated with El Niño-Southern Oscillation (ENSO) amplify the impacts of steadily increasing temperatures. For example, coral communities in the Galápagos Islands experienced mortality rates of up to 95-99% during severe ENSO warming in 1982-1983. Persisting through such extreme conditions imposes additional challenges to survival in already marginal environments for coral growth and development that occur in the eastern tropical Pacific. This study quantifies via photoquadrats population changes in mean live coral cover, density, and colony size over a 7-year period (2004-2011) in a small community of the nodular coral Psammocora stellata located at Xarifa Island in the Galápagos Islands. The physical characteristics of this shallow (1-3 m depth) habitat include shading by tall basalt cliffs and strong water flushing action that may contribute to the persistence of this species at this atypical locality through mitigation of anomalously warm and cold conditions.Coral cover is high for this region, and significantly increased from 39.7% in 2004 to 58.3% in 2011 (p=0.006, Tukey HSD), an overall increase of 47%. Fluctuations in coral cover were associated with anomalous temperatures (up to +3.5° and -4.6° C compared to daily means). Negative temperature anomalies in 2007 were associated with a non-significant decrease in coral cover (55.3% in 2007 to 49.5% in 2009), and coral cover rebounded in 2011 to 58.3%. From 2004 to 2011 colony density increased significantly, from 258±62 to 612±245 colonies m-2 (p2 (pin situ, documenting values that ranged from 16.8° - 28.9° C. The persistence of the Psammocora community through both strong and moderate ENSO events demonstrates the resistance and resilience of the species to these temperature anomalies. Adding to the understanding of this species and its interactions with the surrounding physical processes will aid in the development and improvement of management strategies.