Research Technical Report

Examining Diver-Operated Stereo-Video as a Benthic Surveying Tool in Temperate Rocky Reef Habitats

Leggett, T., S.I. Lonhart, and J. Lindholm (April 2023)

Oral presentation at AAUS Diving for Science Symposium, 23-29 April 2023, Pensacola, FL

ABSTRACT

Kelp forest degradation continues along California’s coastline and government and citizen monitoring efforts expand in response. Historically, monitoring programs have relied on underwater visual census (UVC) surveys to produce diversity and abundance estimates of nearshore organisms and uniform point contact surveys (UPC) to describe habitat complexity. As researchers attempt to scale up monitoring efforts, surveying practices may need to be equally scalable. Imagery-assisted monitoring is a possible solution and currently contributes to intertidal and surface monitoring efforts but has yet to see adoption in subtidal habitats. To address this, we compared benthic organism population metrics and habitat characteristics between diver-operated stereo-video (stereo-DOV) and UVC surveys in kelp beds and barren reefs. The influence of angle on estimates was examined by conducting stereo-flight at two angles, 45° and 90°. In kelp beds, pairwise comparisons of linear mixed effect models revealed UVC estimated significantly greater (Tukey’s HSD, p <0.05) benthic invertebrate diversity (Shannon-Wiener Diversity Index), species richness, adult canopy and subcanopy forming algae density, and giant kelp stipe density when compared to both stereo-DOV angles (45° and 90°). However, in urchin barrens, both stereo-DOV angles produced comparable diversity estimates to UVC surveys. No differences (Tukey’s HSD, p >0.05) were observed between stereo-DOV angles for invertebrate diversity, algae density, or stipe density in either habitat. UPC and stereo-DOV comparisons are underway, but preliminary findings parallel the muted responses produced by stereo-DOV when compared to UVC. Our findings suggest stereo-DOV surveys can be a valuable tool for monitoring urchin barrens and rapidly collecting benthic data in the field. Future research is needed to optimize the use of stereo-technologies in this capacity in other conditions and habitats.