Seasonal planktonic food web structures

Using these long-term zooplankton biomass data, along with multi-year phytoplankton biomass estimates, we constructed three food web models for the plankton community in the SoG using Ecopath (https://ecopath.org/). Each model provides a steady-state, but seasonally-varying, mass balance in one of three seasons in the SoG: spring, summer, and winter. Our models describe the plankton community using fifteen functional groups, with variations in biomass, diet, and growth and consumption rates. These functional groups include heterotrophic bacteria, phytoplankton, mixotrophic microzooplankton, and mesozooplankton.

The models indicate that the planktonic component of the food web in the Strait of Georgia spans 3 trophic levels. All mesozooplankton have lower trophic levels in the spring than the other two seasons, indicative of the shift to more herbivorous activity in this season. After the spring bloom, microzooplankton increase in dominance and zooplankton diets shift to reflect this change in food availability, increasing their trophic position.

These taxonomically diverse, seasonal models give insights into how energy pathways and trophic interactions within the plankton community vary between the seasons. These structural changes within the plankton food web throughout a year have implications for higher trophic levels, including the seasonal availability and quality of food for plankivorous fish. Further, they can be applied to nutrient cycling, detrital sinking, and contaminant bioaccumulation through the food web.