Evidence of seabird guano enrichment on a coral reef in Oahu, Hawaii
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Seabirds and coral reefs are two of the most threatened marine communities on earth, and they co-occur on many tropical islands and subtropical islands and atolls. Seabirds concentrate marine-derived nutrients on breeding islands in the form of feces (guano), and these nutrients dramatically alter terrestrial ecosystem ecology. Recent work in the remote Pacific indicates seabird-derived nutrients may also subsidize nearshore coral reefs, but the consequences of guano on complex, anthropogenically modified coral reefs are unknown. The impact of seabird guano on nearshore coral reefs around Moku Nui, an islet with a large seabird colony in Oahu, Hawaii, was investigated in comparison with coral reefs around three islets with lower seabird abundance. Reefs in close proximity to Moku Nui (where thousands of wedge-tailed shearwaters, Puffinus pacificus, breed) had greater concentrations of dissolved phosphate in seawater and greater δ15N in adjacent subtidal macroalgae relative to reefs next to smaller breeding colonies. However, dissolved nitrate was not different among islets. These results indicate that seabirds may be a source of nutrients for the waters surrounding Moku Nui that are already inundated with local and global stressors.
KeywordsCoral Reef Macroalgae Stable Isotope Analysis Halimeda Seabird Coloni
We are grateful to the faculty and staff at the Hawaii Institute of Marine Biology for assisting in the logistics of this work, particularly F. Thomas, R. Toonen, and J. Jones. We thank G. Marino for fieldwork assistance. We acknowledge B. Patel, K. Mattingly, R. Tallman, J. Bachellier, D. Pruitt, K. McElroy, K. Kopecky, B. Buttler, and J. Walden for laboratory assistance. We thank R. Brainard for suggesting the study site, assistance with experimental design, and editing the manuscript. We thank P. Raimondi, D. Croll, B. Tershy, J. Estes, and M. Beck for their assistance with experimental design, statistics, and editing of the manuscript. We thank M. Foley, R. Franks, and D. Andreasen for their assistance with seawater and stable isotope analyses. We thank A. Marie, L. Young, and the Hawaii Division of Forestry and Wildlife for information on seabird population ecology. Finally, we acknowledge the following funding sources: National Science Foundation Doctoral Dissertation Improvement Grant (#1110815), the Friends of Long Marine Lab Student Education and Research Award, Myers Trust, Center for Tropical Research in Ecology, Agriculture, and Development (CenTREAD) tropical research grant, and Ecology and Evolutionary Biology graduate research and travel grants from the University of California Santa Cruz. No permits were necessary in the collection of algae for this work.
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