Field samples of giant kelp canopy blade reflectance and
chlorophyll a, chlorophyll
c, and fucoxanthin pigment concentration were
taken at five kelp forest sites along the California coast: Arroyo
Burro, Arroyo Quemado, and Mohawk kelp forests in the Santa
Barbara Channel, La Jolla kelp forest near San Diego, and Pleasure
Point kelp forest near Santa Cruz. Sites in the Santa Barbara
Channel were sampled monthly over a three-year period (August 2012
– August 2015) and the La Jolla and Pleasure Point sites were
sampled quarterly (May 2013 to July 2015). One mature blade
(approximately 14 days of age) was collected 2 meters back from
the tip of an actively growing frond from 15 different plants at
each site. Blades were placed in a sealed plastic bag which was
immediately placed on ice in an opaque cooler. The blades were
then transported to the lab where they were stored at 4°C until
being processed within 24 hours of collection.
A 5 cm square was cut from the center of each blade approximately
5 cm above the pneumatocyst and any epibionts were removed (blades
usually had no epibionts). The reflectance of the square was then
measured between 350 – 800 nm, at 1 nm intervals, using a Shimadzu
UV 2401PC spectrophotometer with an integrating sphere attachment.
Pigment concentration was determined from a 0.8
cm2 disc excised from the center of
each square. Each disc was weighed and placed in 4 mL of dimethyl
sulfoxide for 45 minutes at room temperature in the dark. The disc
was then removed and washed with 1 mL water, bringing the total
volume of the first extraction to 5 mL, before being placed in 5
mL of a 3:1:1 acetone, methanol, and water solution for 2 hours at
4°C in the dark. The extractions were placed in individual quartz
cuvettes and absorbance was measured between 350 – 800 nm using
the spectrophotometer. Pigment concentrations were determined
using known absorbance-based equations (Seely et al. 1972).
References:
Bell, T.W., Cavanaugh, K.C., Siegel, D.A. (2015) Remote monitoring
of giant kelp biomass and photosynthetic condition: An evaluation
of the potential for the Hyperspectral Infrared Imager (HyspIRI)
mission. Remote Sensing of Environment, 167,
218-228.
Bell, T.W., Reed, D.C., Nelson, N.B., Siegel, D.
A. (2018), Regional patterns of physiological condition determine
giant kelp primary production dynamics. Limnology and
Oceanography, 63, 472-483.
Bell, T.W., Nidzieko, N., Siegel, D.A., Miller, R., Cavanaugh,
Ky., Nelson, N., Reed, D., Federov, D., Cavanaugh, Ka., Moran,
C., Snyder, J., Griffith, M. (2020), The utility of satellites and
autonomous remote sensing platforms for monitoring offshore
aquaculture farms: A case study for canopy forming
kelps. Frontiers in Marine Science,
7:520223.
Bell, T.W., Siegel, D.A. (2022), Nutrient availability and
senescence spatially structure the dynamics of a foundation
species, Proceedings of the National Academy of
Sciences, 119, 1, e2105135118.
Seely, G., Duncan, M., Vidaver, W. (1972) Preparative and
analytical extraction of pigments from brown algae with dimethyl
sulfoxide. Mar. Biol. 188.
