A Rapid Ecological Assessment (REA) Quantitative Survey Method for Benthic Algae Using Photoquadrats with Scuba

The challenge of assessing seldom-visited, benthic substrates has created the need for a method to describe benthic communities quickly and efficiently. Macroscale rapid ecological assessments (REAs) of algal assemblages provide managers of coral reefs and other benthic ecosystems with the fundamental descriptive data necessary for continued yearly monitoring studies. The high cost of monitoring marine communities, especially remote sites, coupled with the time limitations imposed by scuba, require that statistically valid data be collected as quickly as possible. A photoquadrat method using a digital camera, computer software for photographic analysis, and minimal data collection in the field was compared with the conventional method of point-intersect (grid) quadrats in estimating percentage cover in subtidal benthic communities. In timed studies, photoquadrats yielded twice the number of quadrats (and an almost infinite number of data points) as conventional methods, provided permanent historical records of each site, and minimized observer bias by having only one observer identifying algae in the field. However, photoquadrats required more post-collection computer analyses of digital photographs than conventional methods. In the manual method, observer bias in algal identification can occur depending on the degree of experience of individual divers. On the other hand, photoquadrats rely on one observer in the field and one observer in the laboratory, standardizing algal identification. Overall, photoquadrats do not yield the finer resolution in diversity that was found using point-intersect quadrats but do provide a more precise estimate of percentage cover of the abundant species, as well as establishing a permanent visual record in the time allowed by work with other teams. EXTENDING OVER 1930 km northwest of Kaua'i in the main Hawaiian Islands is the Northwestern Hawaiian Islands (NWHI) Coral Reef Ecosystem Reserve: 257,700 km of marine reserve that was created by presidential executive order in 2000. Since the 1 This project was supported by the Botany Department, University of Hawai'i at Manoa; Hawai'i Coral Reef Initiative (HCRI); and the National Oceanic and Atmospheric Administration. Manuscript accepted 27 May 2003. 2 Department of Botany, University of Hawai'j at Manoa, 3190 Maile Way, Honolulu, Hawai'i 96822. 3 Coral Reef Ecosystem Investigation, Honolulu Laboratory, National Marine Fisheries Service, 1125B Ala Moana Boulevard, Honolulu, Hawai'j 96814. Pacific Science (2004), vol. 58, no. 2:201-209 © 2004 by University of Hawai'i Press reserve's instatement, the Coral Reef Ecosystem Investigation (U.S. National Marine Fisheries Service) and the Division of Aquatic Resources (Department of Land and Natural Resources, State of Hawai'i) have conducted yearly and biyearly, respectively, assessment and monitoring research expeditions to the numerous islands and reefs situated in this remote part of the Pacific. These trips have included oceanographers and algal, coral, fish, and invertebrate biologists in a cooperative effort to quantitatively assess this isolated and relatively untouched ecosystem. Teams of biologists have conducted surveys to record the flora and fauna using rapid ecological assessment (REA) protocols with scuba. As the name implies time was limited, thus requiring carefully designed methods for quantitative data collection. The goal of the algal surveys was to describe the algal community