Recent (post-1930) changes in the extent of subtidal seagrass (Zostera muelleri) beds of the eastern Bay of Islands, New Zealand

Study Extent

Sampling

Method steps

1. Aerial images useful in defining the extent of the main subtidal seagrass beds over time were scanned/downloaded, with particular focus on early (pre-satellite) ones. The aim was to acquire a time-series, with at least one image every decade through to the present, that could be used to identify any large-scale (on the order of ≥20%) changes in the seagrass footprint. High-resolution imagery spanning multiple beds was particularly useful because such depictions typically included well-established beds that provided reference for smaller and less well-known ones. Images taken at intervals shorter than a decade – even those separated by a year – were also useful because they could potentially indicate how much the surface manifestation of the seagrass beds changed over short timeframes. (Although plant-condition is important in the dynamics of seagrass, this is not readily assessed from aerial imagery. As it turned out, almost all images were from spring and summer, when this seagrass is typically most lush.

1. Zostrea muelleri
   common name: Seagrass rank: species