Variation in algal turf species composition and abundance on two Hawaiian shallow subtidal reefs

In the tropics, algal turfs are a key marine community, floristically and ecologically, yet the turf structure and its spatial and temporal variation have seldom been quantitatively assessed. We compared species composition and abundance of turf algae on two shallow subtidal reefs (< 2 m deep) on the island of Hawai‘i from September 2000 to July 2002. Of the 102 species of marine algae identified in the algal turf community, 17 belonged to the Chlorophyta, 9 to the Phaeophyta, and 76 to the Rhodophyta. Red algae dominated the turfs at both sites. Species richness, species diversity, and evenness varied between sites and among sampling dates, perhaps due to differences in substratum, precipitation and wave exposure. The most abundant turf species (Ceramium macilentum J. Agardh, Pterocladiella caerulescens (Kützing) Santelices et Hommersand, Hypnea spinella (C. Agardh) Kützing, Coelothrix irregularis (Harvey) Børgesen, Amansia glomerata C. Agardh and Laurencia brachyclados Pilger) showed very patchy spatial distributions and variable seasonal abundances. 38 new records for the island of Hawai‘i were documented, many of which were common. Although growth form rather than dominant or diagnostic species defines the algal turf community, identification and monitoring of individual species, which have different reproductive and physiological characteristics, are essential to understanding the ecology of the turf.