Abstract Summary
The spatial context in which species interactions occur strongly influences an ecosystem’s resilience and ability to recover after disturbance events. Therefore, understanding how spatial interactions impact coral growth, recruitment, and diversity is of paramount importance when restoring a degraded coral reef ecosystem. On Palmyra, a remote atoll in the equatorial Pacific, the corallimorpharian Rhodactis howesii has dramatically increased in abundance and now dominates >3 km2 of reef, displacing hard corals and other dominant biota in the process. To curtail further ecosystem degradation, a restoration experiment was established at the epicenter of the corallimorph outbreak. Restoration was initiated by removing corallimorph to create a bare CaCO3 substrate, which was accomplished by tenting and application of granulated bleach for 48-hours followed by manual removal of remaining corallimorph tissue fragments. Of the 12 9m2 treatment plots created, 9 plots received coral transplants and the remaining 3 were designated as treatment controls. Coral fragments of Acropora acuminata (n = 27), Pocillopora damicornis (n = 27), and Montipora capitata (n= 27) were collected from nearby regions of reef unaffected by the corallimorph outbreak and transplanted with non-toxic two-part epoxy. Fragments were transplanted in same-species aggregations, aggregations consisting of all three species, and non-aggregated arrangements to determine how spatial distribution impacts growth among corals with varying competitive abilities and life history strategies. Four years post establishment, the restoration site has experienced nearly a 300% increase in coral cover due to growth of original transplants. Plots in which corals were transplanted in aggregations consisting of three different coral species had the highest amount of coral recruitment and an additional 100% increase in coral cover due to prolific A. acuminata growth. Corallimorph reinvasion in treatment plots has been negligible. The methods used to produce this restoration experiment can be applied to other locations around Palmyra to effectively mitigate further expansion of the corallimorph throughout the atoll. Moreover, aspects of these methods, such as multi-species coral transplant aggregation and substrate preparation, could benefit coral reef restoration programs aiming to limit biological invasions, enhance coral cover and diversity, and improve branching Acropora growth rates.
