Multispectral low altitude remote sensing of wild oyster reefs

Abstract

Although wild oyster reefs are invasive and are trophic competitors, they are an essential component of intertidal rocky reef systems that support a wide range of biodiversity in some intertidal estuaries. Despite their importance, their population locally and globally are declining, reflecting variations such as increased predation and anthropogenic influence in an estuary, such as excessive nutrients discharge. In addition, spatial assessment and mapping wild oyster reefs can be challenging due to complex and rugged structures that are challenging to access using conventional in-situ, time-extensive techniques. Therefore, the application of remote sensing for ecology and conservation of benthic habitats has emerged as a powerful technique to expedite many challenges. This study investigated VIS (visible spectrum) and VIS+NIR (visible + near-infrared spectrum) remote sensing for spatial assessment and mapping wild oyster reefs in a rocky intertidal reef at low tide. In addition, the study assessed the spectral reflectance signatures of wild oyster reefs from RPAS aerial imagery to in-situ spectral signatures. Although the VIS orthomosaic had a higher spatial resolution, wild oyster reefs detection was less efficient. In contrast, oyster reefs were correctly classified in the VIS+NIR imagery achieving an overall accuracy of 85%. This accuracy implies that the spectral resolution has been more critical to detect and correctly classify oyster reefs than spatial resolution. This remote sensing technique for ecology and conservation offers scale-appropriate spatial assessment, monitoring, and mapping of benthic habitats in challenging and inaccessible marine environments. Furthermore, this technique can be complemented with in-situ and other remote sensing datasets to enhance our understanding of the spatial dynamics of near-shore marine environments.