Wave exposure explains some of the variation among benthic communities at Pearl and Hermes Atoll, study proves

Pearl and Hermes Atoll, located at 27°50′ N, 175°55′ W, is the largest atoll in the Northwestern Hawaiian Islands (NWHI) and part of the Papahānaumokuākea Marine National Monument, one of the largest marine conservation areas in the world. A recently published paper (Page-Albins et al. 2012; see the abstract and reference below) presents the most comprehensive synthesis of benthic data on both corals and algae to date for this atoll, a study that provides a baseline for future management and monitoring efforts there.

NOAA Fisheries and the NOAA Office of National Marine Sanctuaries and other partners in a multiagency, interdisciplinary effort have conducted assessment and monitoring surveys of the benthic communities and fish assemblages in the NWHI on an annual basis since 2000. Photographs taken at 17 Rapid Ecological Assessment (REA) sites at Pearl and Hermes Atoll during the PIFSC cruise aboard the NOAA Ship Townsend Cromwell in September 2002 were used in the Page-Albins et al. (2012) study.

Benthic cover was determined from image analysis of 406 photographs from 34 transects in 4 different wave-exposure zones at Pearl and Hermes Atoll. Wave exposure can result in disturbance on coral reefs and contributes to general water motion and circulation across reefs.

Peter Vroom and Ronald Hoeke, a phycologist and an oceanographer who work or worked for the PIFSC Coral Reef Ecosystem Division, contributed to this study, which was led by Kimberly Page-Albins, formerly of the Joint Institute of Marine and Atmospheric Research of the University of Hawai`i at Mānoa and now of the Department of Zoology of Oregon State University.

The results of this study describe and explain patterns in the structure of benthic communities at Pearl and Hermes Atoll, providing a tool to make predictions about community assemblages in the NWHI on the basis of knowledge of wave exposure.

Page-Albins KN, Vroom PS, Hoeke R, Albins MA, Smith CM. 2012. Patterns in benthic coral reef communities at Pearl and Hermes Atoll along a wave-exposure gradient. Pacific Science 66(4):481-496. doi:10.2984/66.4.6

This study compares percentage cover of benthic organisms at the species level at Pearl and Hermes Atoll (PHA), the largest atoll in the Northwestern Hawaiian Islands, to determine (1) the degree of difference among sites, (2) whether wave-exposure zones explain observed patterns in benthic community structure, and (3) whether species richness differs among wave-exposure zones. Thirty-four sites were surveyed representing four categorical wave-exposure regimes: high, intermediate-high, intermediate-low, and low. A two-way nested analysis of similarity (ANOSIM) found significant differences among sites and that wave exposure explained some, but not all, of this variation. High and low wave-exposure zones were found to differ significantly from other zones. Low wave-exposure sites exhibited the highest similarity to each other and were dominated by the finger coral Porites compressa (38% cover). High wave-exposure sites were also similar to each other and were dominated by crustose coralline red algae (37% cover). Sites within the intermediate-high zone exhibited substantial variability; however, the presence of the green alga Microdictyon setchellianum was a unifying characteristic among many sites in this zone. Finally, intermediate-low wave-exposure sites exhibited the greatest degree of variability among sites and also exhibited the greatest level of benthic species diversity, including presence of rarer species. Wave exposure proved a useful tool in describing the diverse assemblages of benthic communities at PHA, especially for sites experiencing extreme high and low wave exposure.

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