Spatial and Temporal Comparisons of Benthic Composition at Necker Island, Northwestern Hawaiian Islands

Abstract

Necker Island, a remote island located in the Northwestern Hawaiian Islands, provides a unique opportunity to investigate species-level algal and benthic invertebrate assemblages and assess temporal variation of coral reef ecosystems exposed to minimal anthropogenic impacts. This study provides a robust baseline of common benthic species at Necker Island and their relative abundances before any known ecological response to changing oceanographic conditions. Rapid ecological assessment (REA) methods using photoquadrat imagery from long-term monitoring sites coupled with towed-diver surveys conducted between 2002 and 2006 were analyzed to determine percentage cover of benthic organisms around the island, and macroalgal species lists were compiled from voucher specimens. Benthic substrates were typically dominated by turf algae at all sites for all years, and macroalgal and coral covers were found to be low. A total of 25 macroalgal and 11 anthozoan species was identified. Of these, 13 macroalgal species and one coral species represent new records for Necker Island. Analyses of community similarity found spatial differences among sites in 2006, as well as temporal differences between 2005 and 2006, an outcome primarily driven by significant increases in percentage cover of macroalgae and coral at one site. However, benthic communities observed during extensive towed-diver surveys around Necker Island did not identify significant differences among geographical sectors or years, suggesting that benthic communities are relatively homogeneous. Necker Island contains macroalgal and coral populations similar to those of neighboring reef systems within the Northwestern Hawaiian Islands, and this study provides a baseline of benthic assemblages for ongoing temporal monitoring.