UC San Diego

Invasive and opportunistic species are known to cause turnovers in dominant taxa by rapidly monopolizing space following disturbance events, often producing lasting shifts in community structure provided that environmental conditions remain favorable. On Palmyra Atoll, the corallimorph Rhodactis howesii has become highly invasive and now covers > 3 km2 of reef radiating outward from a ship grounding that occurred in the early 1990s. In 2014, our team established a corallimorph removal and coral transplantation experiment within the epicenter of the corallimorph outbreak, following shipwreck removal, to determine if restoration is a viable option for recovering previously dominant reef-building taxa. Monitoring of the restoration site ran from 2014-2018 and consisted of annual surveys to assess changes in benthic community structure. By 2018, corallimorph reinvasion in experimental plots where it had been previously removed was negligible and in control plots, corallimorph cover decreased by 99%. Across the entire site, coral cover increased by 392%, turf and crustose coralline algae have dominated the remaining benthos, and coral recruits have been observed as well. Additionally, variations in growth rate and asexual propagation among coral transplant species appears to influence benthic community succession. Methods used within this study provide an effective strategy for protecting localized regions of reef most vulnerable to corallimorph invasion, namely those possessing low coral cover and in the initial stages of corallimorph invasion. Additionally, these results suggest that active reef management or restoration can drive changes benthic community succession, but only if the underlying causes of degradation have been removed.