Marine Biology Terms Starting With F

Filter Feeder is an animal that obtains food by drawing water across or through specialized structures that retain suspended particles such as plankton, bacteria, and organic detritus while allowing water to pass through.

Filtering structures differ widely across animal groups: bivalves like oysters pass water over mucus-coated gills, baleen whales force water through fibrous keratin plates, and sponges pump water through microscopic pores called choanocytes. A single eastern oyster (Crassostrea virginica) can filter up to 50 gallons of water per day, removing phytoplankton, bacteria, and suspended sediment in the process. This feeding activity links primary producers directly to larger consumers and transfers energy up the food web without the pursuit behavior seen in predators.

Dense oyster reefs historically kept Chesapeake Bay water clear enough for submerged grasses to grow at depths exceeding 2 meters, demonstrating how filter feeders can shape entire ecosystems.

Fish Migration is the regular, directional movement of fish between two or more distinct habitats, driven by reproductive, feeding, or environmental cues and often timed to specific seasons or life-history stages.

Some migrations are vertical, with species like lanternfish (family Myctophidae) ascending hundreds of meters to surface waters each night to feed and descending to depths exceeding 500 meters by day. Others span entire ocean basins: Atlantic bluefin tuna (Thunnus thynnus) cross the Atlantic Ocean multiple times per year, traveling more than 9,000 kilometers between feeding grounds off Newfoundland and spawning areas in the Gulf of Mexico or Mediterranean Sea. Anadromous species such as Pacific salmon hatch in freshwater, spend years maturing in the ocean, and return to their natal streams to spawn, navigating by magnetic fields, olfactory cues, and celestial orientation.

These movements link nutrient cycles across ecosystems, as salmon carcasses deposit marine-derived nitrogen deep into riparian forests after spawning.

Fjord is a long, narrow, steep-sided coastal inlet formed when a glacially carved valley was flooded by rising sea levels after the retreat of glacial ice, typically characterized by a shallow bedrock sill at its mouth and a deep basin farther inland.

Glaciers erode bedrock far below sea level, so fjord basins can exceed 1,300 meters in depth, as seen in Sognefjord in Norway, the world’s deepest fjord at approximately 1,308 meters. The shallow sill at the mouth restricts water exchange between the deep basin and the open sea, causing oxygen depletion in bottom waters where organic matter accumulates and decomposes. Freshwater from snowmelt and glacial runoff forms a low-salinity surface layer that floats above denser seawater, creating sharp vertical stratification.

Cold, nutrient-rich conditions in fjords support productive food webs that include cold-water corals, Atlantic cod, and seabird colonies that nest on the surrounding cliffs.