Mapping and Monitoring Floating Kelp Canopies in Washington State

Canopy-forming kelp is a important contributor to the detritus-based food web and provides habitat for a wide range of fish, birds, and invertebrates. In Washington State, we have mapped canopies of Nereocystis luetkeana and Macrocystis pyrifera since 1989 using a variety of methods including color-infrared aerial photography, multispectral remote sensing, and  helicopter-based videography. These diverse datasets provide substantial information on kelp distribution, and are distributed to support planning and research activities. Information on trends in floating kelp canopies over time is available from one sub-area where annual surveys have taken place since 1989 (the Strait of Juan de Fuca and the outer coast). Kelp canopies have increased significantly (p<0.05) over two decades along the Strait of Juan de Fuca and outer coast. These long term data also suggest strong climate impacts on total kelp canopy area. While kelp canopies throughout the area are increasing, some sub-areas are stable or decreasing, which demonstrates the important role played by local environmental factors. Within Central and South Puget Sound, long term trend information is lacking, but limited review of historical surveys suggest that extensive losses may have occurred in kelp canopies.