Patterns and control of primary production
Standing crop and productivity of giant kelp
Giant kelp (Macrocystis pyrifera) is the world's largest alga and is one of the fastest growing autotrophs on earth. We are studying patterns and causes of variation in net primary production (NPP) by giant kelp at three sites in the Santa Barbara Channel (Arroyo Burro, Mohawk and Arroyo Quemado) using an approach that consists of monthly field measurements of standing crop and rates of biomass loss. We combine these data with a simple model of kelp dynamics to estimate specific growth rates and NPP for each season of each year. These methods in part follow a conceptual approach common in terrestrial studies that calculate NPP by measuring accumulation and loss of biomass. We are using these and other data to explore the physical, chemical and biological factors controlling growth and NPP in giant kelp.
Optical estimates of kelp biomass and productivity
Field based estimates of NPP are labor-intensive and thus limit the spatial scale of possible comparisons. With collaborative funding, we are exploring the use of optical information from remotely sensed hyperspectral imagery (PHILLS and SAMSON) to estimate the productivity and biomass of giant kelp canopies along the California coast. The consistent optical signature of the kelp canopy produces a blade area index (BAI) that is linearly related to diver estimates of kelp abundance. This correlation allows retrieval of standing crop biomass and productivity from remotely sensed below canopy irradiance and above canopy reflectance.