Quadrat vs. video assessment of macroalgae cover: a methods comparison

In 2004–2007, the beaches of Sanibel Island, Florida, were affected by large drifts of macroalgae that accumulated on shore. The adjacent seafloor is composed of three ecoregions: inshore, nearshore and offshore. To measure attached and unattached macroalgae on various substrata, two field survey methods were compared from 2008 to 2010 along thirteen 100 m long transects. One method used visual assessments of macroalgae in 1 m² quadrats along the transects and one used an underwater camcorder to capture video footage along the transects. Results of each method were converted to percent cover of the transect and compared for each sampling date. The results showed that digital video observations were not significantly different than diver assessments for two of three ecoregions. Sparse amounts of macroalgae were underestimated nearshore using visual SCUBA, due to the inconsistent, but high percentage, of algae cover. Uses, advantages, disadvantages, and time-effectiveness of the two methods were compared. Natural resource managers can choose which survey method meets their scientific, management and budget needs. Based on these results, it is suggested that video analysis of bottom cover is a practical method for rapid, widespread assessment of macroalgae abundance surrounding Sanibel Island.