AEBR 366 Satellite derived national time series of giant kelp (Macrocystis pyrifera) abundance and key environmental drivers

Tait, L.W.; Pearson, R.; Whiteside, A; Thoral, F.; Mangan, S. (2025). Satellite derived national time series of giant kelp (Macrocystis pyrifera) abundance and key environmental drivers. New Zealand Aquatic Environment and Biodiversity Report No. 366. 50 p.

Giant kelp is one of the largest and fastest growing seaweeds in the world, it provides food and habitat for marine life, and engineers the physical environment around it. It is also a managed fishery in Aotearoa New Zealand. Because of its key role in supporting marine fisheries (particularly pāua, kina, kōura, and several key finfish) and the increasing interest in the commercial harvesting of seaweeds, we need a greater understanding of the current distribution of giant kelp.

Here we utilise satellite remote sensing to track the distribution of giant kelp across Aotearoa New Zealand over the last decade. Satellites provide a passive and free tool for monitoring the expanse of surface canopies. This is particularly relevant as kelp forest ecosystems are impacted by extreme events such as marine heatwaves and cyclones.

We show that satellite remote sensing of giant kelp can be used effectively to track the status and health of giant kelp which provides a powerful tool for identifying the drivers of change in kelp beds. By looking for relationships between key environmental parameters and kelp forest coverage, we found that national level declines in giant kelp beds are highly associated with periods of warmer oceanic conditions.

We provide a summary of regional trends of giant kelp coverage and assess the environmental factors that drive variation. This work is accompanied by a web interface that allows managers and stakeholders to view and assess satellite products and the outputs of our kelp cover estimates.

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