- Fauna
- animal life of a region, special environment
- Feces
- excrement
- Fecund
- fertile or capable of producing many offspring
- Feduncity
- capacity, especially in female organisms, of producing eggs, sperm, or offspring in great numbers
- Feral
- individuals of a domesticated species that have returned to a wild state
- Festoon
- string
- Filamentous
- chainlike series of cells as in many algae
- Filaments
- fine or threadlike structures
- Filter feeder
- animal that eats by passing surrounding water through a filtering device and filtering or straining out small particles of food
- Fission
- form of asexual reproduction in which the parent organism divides into two or more parts, each becoming an independent individual
- Float
- gas containing structure found on the stem of large kelp that buoys up the plant; pneumatophore or pneumatocyst
- Flora
- plant life of a region, special environment, or period of history
- Flukes
- two lobes of a cetacean or dugong's tail
- Flyway
- route followed by migrating birds. There are four major north to south routes in the US.
- Food chain
- progression of feeding levels in which one organism is the food source for the next level
- Food web
- description of the interactions or complex relationships between various food levels
- Forage
- food for animals, especially when taken by browsing or grazing; to search for food
- Fossil
- hardened remains or traces of plant or animal life of a past geological period; usually preserved in rock
- Fouling
- mass of living and non-living bodies and particles attached to a submerged object
- Frond
- leaf-like structure of a plant: kelp stipe (stem-like part) and the attached blades
- Fusiform
- spindle or torpedo shaped; rounded, broadest in the middle and tapering toward each end
