Bull Kelp Monitoring
Floating bull kelp (Nereocystis luetkeana) is important habitat for marine invertebrates, such as pinto abalone, and marine fishes, including forage fish and the endangered rockfish bocaccio (Sebastes paucispinis). However, the distribution and area of bull kelp beds in Puget Sound is not regularly monitored, so changes in abundance of this critical habitat would be poorly documented.
BOAT-BASED BED SURVEYS
Since 2015, the Island County MRC has collaborated with the Northwest Straits Commission to conduct annual boat-based surveys of selected beds (see map below). Using handheld GPS units and kayaks, volunteers map the perimeter of beds and collect accessory data such as surface water temperatures and bed depth estimates. They conduct monthly surveys during the bull kelp growing season at a zero-foot tidal height. In addition to mapping, surveyors also record observations of animals using kelp beds.
One observation is that the beds under strong river influence (Lowell Point and Polnell Point) have a very different monthly growth pattern than the bed with consistent marine influence (Ebey's Landing).
Bottom temperature measurements show that in August, there are large differences among the sites. Ebey's Landing exhibited little variation in bottom temperatures throughout the bed, and had the lowest mean temperature of 13.5°C. Polnell Point exhibited the widest variation in temperatures and had a mean of 16.2°C. Possession Point had relatively high bottom temperatures throughout the bed and had the highest mean temperature of 17.0°C.
See some of the inhabitants of bull kelp beds!
- Tubesnouts feeding in the kelp bed
- Rockfish (possibly a copper) hiding in the kelp forest
- Submerged aquatic vegetation beneath bull kelp with shiner perch, forage fish, and kelp perch
- Herring school! (& a tubesnout)
- Forage fish (mostly herring) with shiner perch
- Salmon cruising through the kelp forest
- Kelp crabs feasting on bull kelp
- Abundant green urchins in the kelp forest
- Perch (probably kelp perch) & greenling (probably kelp greenling)
In 2017, an aerial component was added to the bull kelp surveys. Photographs using two different angles to the water surface (oblique vs orthogonal) were tested, and paired images were captured using different light wavelengths (visible vs near infrared). These images were used to compile an inventory of bull kelp bed locations along Island County’s shoreline.
Based on the 2017 aerial surveys, an estimate of the length of shoreline with associated bull kelp was determined. At least 21 miles, or ~ 10% of Island County shoreline, has bull kelp beds located in the nearshore zone.