Trophic Resources to Subtidal Suspension Feeders in Kelp Ecosystems

Kelps are highly productive, yet little is known about the fates of kelp primary production. Traditionally, kelps have been assumed to form the base of kelp forest food webs. This assumption extended naturally to suspension feeders, which can comprise up to 80% of the animal biomass in kelp forests and have been hypothesized to consume small particles of kelp sloughing off the extensive surface canopy. Subtidal suspension feeders graze on abundant phytoplankton, but if kelp detritus is a viable food source for suspension feeders, it could be particularly significant during seasonal declines in nutrient concentrations and consequently phytoplankton production. However, direct evidence of kelp detritus assimilation by suspension feeders is scarce: most inference has been based on natural abundance stable isotope analyses which are often based on untested assumptions. To more directly address this problem, we measured kelp detrital sloughing rates and ran experiments to assess kelp particle availability and suspension feeder utilization of naturally occurring kelp detritus when phytoplankton are either abundant or scarce. We have also begun preliminary work to look at alternate pathways for kelp utilization by suspension feeders and detritivores in kelp forests. The bulk of these studies were conducted with two kelp species: Ecklonia radiata in northeastern New Zealand and with Macrocystis pyrifera in Santa Barbara, California. The results of these studies indicate that phytoplankton rather than kelp detritus are the primary food source for subtidal suspension feeders.

Back to: Impacts of Ecological Interactions on Marine Ecosystem Dynamics: New Insights from Models, Theory, and Field Measurements III Posters