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Invasion Mechanisms of the corallimorph, Rhodactis howesii, at Palmyra Atoll /


As coral cover declines globally, management of remaining reefs is increasingly important. Even remote and ̀pristine' reefs are not free from anthropogenic impacts. Biological invasions have been observed in the Pacific Remote Islands Marine National Monument on Palmyra Atoll, a National Wildlife Refuge, and on Kingman Reef. A corallimorph, Rhodactis howesii, was observed on the reefs and is causing phase-shifts on coral dominated habitat. Phase-shifts can lead to loss of ecosystem services by altering the physical structure and characteristics of the reef. The invasions have been linked to shipwrecks at Palmyra Atoll and Kingman Reef. In 1991, a vessel grounded on the Palmyra reef terrace and subsequent growth of R. howesii was observed. The corallimorph now covers ̃2km² of the reef. Rhodactis howesii has also been observed around the wreck at Kingman Reef and the invasion mechanisms are largely unknown. It has been hypothesized that shipwreck iron has added a limiting nutrient to the waters, facilitating corallimorph growth. Population genetics, trace metal analysis, enrichment experiments, and in situ monitoring of the corallimorph were used to test this hypothesis. Results show increasing populations of the corallimorph at both proximal and distal sites to the wreck but a lack of correlation between iron content and proximity to the wreck. Additionally, exposure to shipwreck metal resulted in decreased growth and mortality of the corallimorph, suggesting that metal levels had a toxic effect. These results further an understanding of this invasive species and assist in advancing management strategies on reefs impacted by similar invasions

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