What Is a Filter Feeder?

Learn How Filter-Feeding Works and See Examples of Filter-Feeders

Humpback Whale Lunge-Feeding / Blue Ocean Society for Marine Conservation
A humpback whale lunges vertically to the surface in a feeding maneuver, with its baleen and throat pleats clearly visible. © Jen Kennedy, Blue Ocean Society for Marine Conservation

Filter feeders are animals that get their food by moving water through a structure that acts as a sieve.

Stationary Filter Feeders

Some filter feeders are sessile organisms - they don't move much, if at all. Examples of sessile filter feeders are tunicates (sea squirts), bivalves (e.g. mussels, oysters, scallops), and sponges. Bivalves filter-feed by straining organic matter from the water using their gills.

This is accomplished using cilia, which are thin filaments that beat to produce a current over water over the gills. Additional cilia remove the food.

Free-Swimming Filter Feeders

Some filter feeders are free-swimming organisms who filter the water while swimming, or even actively pursue their prey. Examples of these filter feeders are basking sharks, whale sharks, and baleen whales. Basking sharks and whale sharks feed by swimming through the water with their mouths open. The water passes through their gills, and food is trapped by bristle-like gill rakers. Baleen whales feed either by skimming the water and trapping prey on the fringe-like hairs of their baleen, or gulping in large quantities of water and prey and then forcing the water out, leaving prey trapped inside.

A Prehistoric Filter-Feeder

One interesting-looking prehistoric filter feeder was Tamisiocaris borealis, a lobster-like animal that had bristled limbs that it may have used to trap its prey.

This may have been the first free-swimming animal to filter feed.

Filter Feeders and Water Quality

Filter feeders can be important to the health of a water body. Filter feeders like mussels and oysters filter small particles and even toxins out of the water and improve water clarity. For example, oysters are important in filtering the water of the Chesapeake Bay.

Oysters in the bay have declined due to overfishing and habitat destruction, so now it takes about one year for oysters to filter the water, when it used to take about a week (read more here). Filter feeders can also indicate the health of water. For example, filter feeders like shellfish can be harvested and tested for toxins that could result in paralytic shellfish poisoning.

References and Further Information