The term “bottom feeder” refers to an aquatic animal that primarily forages for nutrition on or within the sediment of the sea floor, consuming detritus, organic waste, or other deposited matter. This behavior is associated with animals like catfish and certain flatfishes that sift through the substrate. The public perception is that these organisms consume waste material, which leads to a misconception about the cleanliness or quality of seafood found near the ocean floor. Scallops, often harvested from the bottom, frequently become mislabeled under this broad and negatively connotated category.
Scallops Are Filter Feeders, Not Bottom Feeders
Scallops are bivalve mollusks, belonging to the same group that includes clams, oysters, and mussels. They are obligate filter feeders, meaning their entire diet is composed of microscopic particles suspended in the water column. This dietary strategy places them in stark contrast to true deposit-feeding bottom feeders that actively consume and process seafloor sediment. The distinction between living on the bottom and feeding on the bottom is important to understand the scallop’s ecology. While many species of scallops rest on the ocean floor, their food source is not detritus, but nutrients extracted from the surrounding water.
The Mechanics of Scallop Feeding
A scallop acquires nutrition by drawing water into its shell cavity using specialized structures. This water is passed over the gills, which serve the dual purpose of respiration and food capture. The gills are lined with tiny, hair-like structures called cilia that beat rhythmically to create a current, pulling water inward. As the water moves across the gills, microscopic organisms are trapped in a layer of mucus. The primary food source is plankton, which consists of both tiny plants (phytoplankton) and small animals (zooplankton). These captured particles are then transported along grooves on the gills toward the scallop’s mouth. The food is ultimately delivered to the stomach and digested in a specialized organ called the digestive gland, ensuring the scallop consumes only organic matter suspended in the water.
Habitat, Mobility, and Diet
Scallops are considered benthic organisms because they live on or near the sea floor. This position is the likely source of the persistent “bottom feeder” confusion, as their location is mistaken for their diet. Many scallop species are not permanently attached to the substrate like oysters or mussels. Most scallops possess a unique method of mobility that distinguishes them from truly sedentary bottom dwellers. They can “swim” in short, rapid bursts by quickly clapping their two shells together. This action expels water, creating a jet-propulsion effect that allows them to escape predators, primarily sea stars. Even when resting on the seafloor, their feeding mechanism remains focused upward into the water column, drawing in suspended particles.