Date

Spring 2024

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The distribution and abundance of rhodolith beds off Santa Catalina Island, California are impacted by natural and anthropogenic factors. These complex, unattached coralline habitats provide food and shelter for important species; however, little is known about temporal variation in bed cover and distribution. Abiotic factors like heavy storms and surge can change bed boundaries and shape. Anthropogenic factors, such as disturbance from mooring chains, can create patchiness within beds. Studies of bed distribution and tracking changes in habitats have historically been done using labor-intensive SCUBA diving. This approach has excellent resolution at small scales but is limited in the temporal and spatial extent across which it can be employed. Emerging technologies, such as drones, may be able to address these limitations and provide an ability to survey large habitat areas beyond those which can be surveyed by SCUBA. Drones may also provide improved data resolution relative to satellite-based approaches to surveying coastal habitat. The objectives of this research were to 1) estimate the best conditions and methods for drones to assess live rhodolith beds, and 2) compare how well drone and diver surveys can be used to assess temporal and spatial shifts in rhodolith bed boundaries. Both drone and diver teams surveyed two beds Isthmus Cove and Emerald Bay at two times in different years. Drones best detected rhodolith beds when flying a lawnmower pattern overhead at 80 m altitude, with a 90-degree camera angle and 80% image overlap. Diver and drone survey methods provided significantly correlated estimates of rhodolith bed perimeter (p=0.039, R2=0.92) and area (p=0.004, R2=0.993), with a non-significant correlation in measuring live rhodolith cover (p=0.533, R2=0.218) due to variability in diver data. These results suggest dronederived estimates of rhodolith bed area and perimeter are comparable and complementary to subtidal SCUBA diver surveys. Drones can thus provide a long-term solution to conducting repeat subtidal surveys and will expand scientists' and resource managers' ability to monitor marine habitat over time.

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