Marine biology is the scientific study of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy. Most marine biologists choose a specialty field such as phycology, ichthyology, invertebrate zoology, marine mammalogy, fishery biology, marine biotechnology, marine microbiology, or marine ecology. Specialization in studying a particular species also is common.