Freshwater Lake Producers: It's Plants and Algae, Not Animals

Primary Production 101

No animals are producers. By definition, producers (autotrophs) synthesize organic compounds from inorganic carbon (CO₂) using light (photoautotrophs) or chemical energy (chemoautotrophs). Animals are consumers (heterotrophs)—they obtain carbon by eating other organisms.

Freshwater Lake Producers

Phytoplankton (Free-Floating Algae)

• Diatoms (silica frustules) – spring bloom dominants.
• Green algae (Chlorophyta) – diverse, year-round.
• Cyanobacteria (“blue-green algae”) – N-fixers; bloom formers (some toxic).
• Dinoflagellates, cryptophytes, chrysophytes – niche specialists.

Periphyton / Biofilms

Algae + bacteria + detritus on submerged surfaces (rocks, plants, sediment). Critical base for grazers (snails, mayflies, tadpoles).

Macrophytes (Aquatic Plants)

• Submerged: Pondweeds (Potamogeton), watermilfoil, elodea, chara (stoneworts).
• Floating-leaved: Water lilies (Nymphaea), spatterdock.
• Emergent: Cattails (Typha), bulrushes, sedges, wild rice.
• Free-floating: Duckweed (Lemna), water hyacinth (invasive).

Chemoautotrophs (Niche)

Sulfur-oxidizing bacteria in anoxic sediments/hypolimnion—minor but non-zero primary production.

Food Web Integration

• Primary consumers (herbivores): Zooplankton (Daphnia, copepods), snails, tadpoles, some fish (tilapia, grass carp), mussels.
• Secondary consumers: Insect larvae, small fish, dragonfly nymphs.
• Tertiary+: Bass, pike, herons, otters, humans.

Why the Distinction Matters

Understanding who fixes carbon drives lake management: nutrient control (P, N) targets algal blooms; macrophyte management balances habitat vs. recreation; fishery yields trace to phytoplankton productivity.