Mapping the relationship of reef structure and surfer spatial patterns at Cloudbreak, Fiji

Area of Science:

• Marine geology
• Oceanography
• Sports science

Background:

• Understanding the relationship between underwater reef topography and human activity is crucial for marine management.
• Surfing, a popular recreational activity, is directly influenced by wave dynamics, which are shaped by reef structures.

Purpose of the Study:

• To investigate the correlation between three-dimensional (3D) reef structure and surfer activity at KuruKuru Mailani (Cloudbreak), Fiji.
• To identify specific topographical features of the reef that attract or concentrate surfer behavior.

Main Methods:

• Combined GPS tracking of surfers with structure-from-motion (SfM) photogrammetry to create high-resolution 3D reef models.
• Analyzed surfer track density, cumulative track length, and various 3D structural variables (e.g., VRM, slope, complexity) across different reef zones.
• Employed multivariate matching, Principal Component Analysis (PCA), and boosted regression trees to link reef structure with surfer activity.

Main Results:

• Surfer activity (density and track length) was significantly higher in the Middle zone of the reef.
• Live coral cover showed no association with surfing activity.
• Specific 3D reef structural elements, including surface ruggedness, curvature, and complexity, were identified as key predictors of surfer concentration, with threshold-like responses observed.

Conclusions:

• The spatial distribution of surfer activity at Cloudbreak is strongly associated with specific ranges of 3D reef topography, rather than live coral cover.
• The developed workflow offers a transferable methodology for analyzing surf-reef interactions at other locations.
• Findings provide insights for marine spatial planning and management of recreational reef environments.