Middle Food Web

The middle food web acts like a bridge — transporting carbon from the tiny photosynthesizers of the lower food web to the large predators at the top.

Filter feeders such as oysters and clams and tiny grazers called zooplankton consume algae (phytoplankton), and as they in turn become food for other species, the organic matter created in the lower web gets passed on throughout the ecosystem.

While zooplankton, particularly copepods, are the most important grazers of the middle food web, not all zooplankton feed on phytoplankton. In fact, most are carnivorous, primarily consuming other zooplankton.

Small fish and gelatinous creatures like ctenophores (comb jellies) and sea nettles also eat zooplankton, playing a large role in keeping phytoplankton-grazing zooplankton in check. In the summer, their predation upon zooplankton is so heavy that it actually exceeds zooplankton reproduction.

Predation on zooplankton, combined with high rates of primary production, ensures that there is excess phytoplankton available to fall to the bottom as detritus — feeding benthic deposit feeders like crustaceans, polychaete worms, and meiofauna (tiny animals that live between grains of sand). In turn, blue crabs — the most dominant predator and scavenger of the Bay’s bottom — feed on these benthic creatures. A blue crab’s diet consists mainly of bivalves, polychaetes, dead fish, and even juvenile blue crabs.

Zooplankton are also a main prey item for suspension feeders such as fish larvae, alewives and herring, bay anchovy, menhaden, and shad. As food for large top predators like striped bass, blue fish, and summer flounder, these small fish of the middle food web act as important go-betweens, enabling carbon to flow to higher levels.