Habitat Complexity and Manta Ray Cleaning Station Use in the Maldives: A Photogrammetric Analysis

2024

James Holloway (MSc - University of Exeter)

Summary: Species interactions are vital for marine ecosystem stability, particularly amid habitat loss and climate change. This study examined manta ray and cleaner wrasse mutualisms at seven Maldivian cleaning stations using novel Structure-from-Motion photogrammetry. While reef rugosity had no significant impact, megafauna richness increased with station volume. Manta ray abundance peaked from April–June and was higher when recorded with Insta360 cameras. Cleaning duration remained unaffected by habitat complexity, suggesting megafauna respond differently than smaller reef species. Photogrammetry proves valuable for future habitat monitoring efforts.

Abstract

“Species interactions are crucial for ecosystem stability, especially as marine biodiversity faces threats from habitat degradation and climate change. Understanding mutualisms such as cleaning interactions between manta rays and cleaner wrasse is vital for guiding conservation efforts. While cleaning station traits such as structural complexity are known to influence smaller reef fish, their effect on manta ray abundance and cleaning behaviour remains unclear. We employed Structure-from-Motion (SfM) photogrammetry, a novel technique for the Maldives, to model habitat complexity (rugosity and volume) at seven cleaning stations. Remote underwater videos (61 deployments, ~64 hours) recorded megafauna from April to December 2023. Megafauna species richness increased with cleaning station volume, while reef rugosity had no significant effect. Manta ray abundance (n = 36) peaked between April and June (mean maxN / hour ± SD = 0.98 ± 1.18) and manta rays were associated with a 41% increase in abundance when using Insta360 cameras compared to GoPro cameras, though cleaning duration was unaffected by habitat complexity. These findings suggest that megafauna may respond differently to habitat complexity than smaller reef species, and highlight the need to consider additional factors such as prey density. This research supports photogrammetry as an effective tool for monitoring reef dynamics and the resulting 3D models provide a valuable reference for future habitat monitoring programs.”

Author Affiliations

  • University of Exeter

  • The Manta Trust

  • The Maldives Manta Conservation Programme