Abstract
Coastal macroalgae worldwide provide multiple ecological functions and support vital ecosystem services. Thereby, it is important to monitor changes in the extent of benthic macroalgal cover. However, as in situ sampling is costly and time-consuming, areal estimates of macroalgal species cover are often based only on a limited number of samples. This low sampling effort likely yields very biased estimates, as macroalgal communities are often characterized by large spatial variability at multiple spatial scales. Moreover, ecological time series are often short-term, making it impossible to assess changes in algal communities over decades and relate this to different human pressures and/or climate change. The Landsat series satellites have operated for 40 years. In the current study, we tested if the Landsat sensors could be used for mapping the cover of shallow water benthic macroalgae. This study was carried out at two sites in the West Estonian Archipelago, in the northeastern Baltic Sea. Our results show that the Landsat imagery accurately reflected both spatial and temporal variability in benthic algal cover. To conclude, the current methodology can be used to improve the existing assessments of areal macroalgal cover, or to estimate the cover values, in areas and times lacking ecological observations.
Highlights
Coastal habitats worldwide are often characterized by lush and diverse communities of benthic macroalgae
Our results show that the Landsat imagery accurately reflected both spatial and temporal variability in benthic algal cover
Instead of targeting only fully cloud-free images, the future applications should determine a lowest threshold of the percentage of available pixels that representatively captures macroalgal patterns, and use this threshold criterion for the image classification and the assessment of macroalgal cover in coastal waters
Summary
Coastal habitats worldwide are often characterized by lush and diverse communities of benthic macroalgae. In these areas, macroalgal communities stabilize sediments, filter nutrients, provide food and shelter for invertebrates, fish, and birds, and support other vital ecosystem services [1,2]. Macroalgal communities stabilize sediments, filter nutrients, provide food and shelter for invertebrates, fish, and birds, and support other vital ecosystem services [1,2] These communities are very dynamic, being shaped by tidal and wave action, upwelling events, coastal currents, and sedimentation, and thereby are often characterized by large spatial patchiness and temporal variability [3]. The areal estimates of macroalgal species cover are often based on a limited number of samples, yielding very biased estimates
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