Quantifying intertidal macroalgae abundance using aerial photography on the Isle of Wight

In 2015 Thomas Bell conducted a master’s research project examining the use of remote sensing data to monitor change in seaweed habitat.

Highlights

• Adapted pre-existing public RGB photographic record for new purpose
• SVM modelling able to separate different habitat classes using RGB DN values
• Isle of Wight intertidal macroalgae abundance has increased in the 21st century

Abstract

Intertidal macroalgae are indicator species whose population changes could be used to track environmental changes, including climate change. Information about their distribution is however difficulty to obtain, as traditional survey methods perform poorly in intertidal environments, necessitating alternatives such as remote sensing. This study assessed intertidal macroalgae abundance over time through analysis of a publically available red-green-blue (RGB) photographic record of the Isle of Wight taken by the Channel Coast Observatory (CCO). The CCO records contain georeferenced aerial surveys from 2001, 2005, 2008, and 2013. A support vector machine model that distinguished between macroalgae classes based on pixel digital number values was trained through the linking of habitat identifications made during ground-truthing to specific pixels in the 2013 CCO images. Four macroalgae classes were included in the model: green algae, red algae, Fucus, and Sargassum. This model was then applied to the entire island for all four surveyed years. Macroalgae abundance increased over the surveyed period, suggesting climate change has not yet detrimentally impacted Isle of Wight macroalgae populations. Fucus abundance increased between 2005 and 2008, while red macroalgae abundance increased linearly with time from 2001 to 2013. Analysis of aerial RGB photography of intertidal macroalgae provides a viable tool to monitor spatial and temporal environmental change.

Citation

Bell T (2015) Quantifying intertidal macroalgae abundance using aerial photography on the Isle of Wight. A thesis submitted for the partial fulfilment of the requirements for the degree
of Master of Research at Imperial College London. Supervised by Juliet Brodie & Chris Yesson. (PDF)

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