Humboldt Bay Eelgrass Survey: Biomass and Plant Density:

The primary natural resource of interest for the Humboldt Bay Natural Resource Management Plan is eelgrass, Zostera marina. This prolific angiosperm is found throughout the intertidal and shallow subtidal habitats of Humboldt Bay interspersed with several species of green algae. Three independent attempts to quantify the distribution and abundance of eelgrass from digitized aerial photographs failed. The technology of the GIS software could not distinguish between Z. marina and the green algae. Marine Advisor Susan McBride and colleagues from the Humboldt Bay Harbor, Recreation, and Conservation Districit and the California Department of Fish and Game completed field work to determine the biomass and plant density of eelgrass at 15 sites in the summer of 2001. Biomass ranged from 0.31 to 0.84 kg fresh weight/m2 and plant densities were between 31 and 198 plants/ m2. Areas with low biomass or low plant density either contained a narrow band of eelgrass or uneven terrain divided by multiple small channels and bare mud, accounting for the lower values. Areas with high biomass and plant density tended to have a more consistent elevation.