TO DIVE OR NOT TO DIVE: SCUBA VERSUS ROV SAMPLING OF MACROALGAE AT 30M DEPTH

Abstract

Spalding, H. L.Moss Landing Marine Laboratories, 8272 Moss Landing, Rd., Moss Landing, CA 95039 USARemotely Operated Vehicles (ROVs) and enriched air Nitrox SCUBA diving have recently become available to researchers for studying the deep‐water environment. Each use a different technique for collecting macroalgal abundance data: ROVs use collections and high‐resolution digital video which can be quantified using an integrative laser and computer imagery program (high tech), while divers often count the densities of individuals and use a point contact method for sampling percent (%) cover in situ (low tech). While the types of data collected by both techniques are the same, the effects of the different sampling methods on data resolution are unknown. As part of a larger study on deep‐water macroalgae in central California, I compared the abundance of common macroalgae (% cover of macroalgal groups and individuals/m2) collected by divers and the ROV Ventana at a depth of 30m at 3 locations in central California. Generally, there were no significant differences between diver and ROV data in the % cover of coralline Rhodophyta, non‐coralline Rhodophyta, and Pleurophycus gardneri/m2. The use of a laser‐calibrated computer imagery program and an ROV with user‐controlled lighting greatly decreased lab analysis time, and a method for sampling macroalgal layers with the ROV was developed. Thus, ROVs with high‐resolution digital video and supplemental macroalgal collections can be used to quantify deep‐water algae as accurately as in situ divers, but without the limited dive time, depth limits, and physical demands of the latter.