The word “epifauna” means those organisms that live on the surface of the water. Episodes can be as short as a day or stretch for centuries, but they always end with significant changes in the living and non-living parts of an aquatic environment.
Many types of crustaceans live in epifaunal communities on the floor of bodies of water such as oceans or fresh-water lakes. These include crabs, lobsters, crayfish (or crawdads), copepods, barnacles, cumaceans (a type of crustacean), and ostracods. Epifaunal animals typically feed on the underlying surface by scraping up food particles from sediment, detritus, or algae matter which is deposited on the floor at low tide, in rain pools, or streams.
What are Epifaunal organisms?
Epifaunal organisms are those that live on the seabed and feed off of it. Epi means “above” or at the top, and phauna is a New Latin word meaning animal.
The word epifaunal was first coined by the Dutch biologist Johannes Thijsse in 1815, to describe invertebrates that live on the seabed and feed off of it. His list included sponges, annelids such as polychaetes and nematodes (Nemas), crustaceans such as amphipods and isopod (Isopoda), arthropods such as echinoderms, insects, mollusks such as Aplacophora.
Epifauna is the accumulation of animals that live on top of water strata. Epifaunal organisms can inhabit both freshwater and marine environments, but they are most common in the former due to the greater abundance of available food sources.
In the broadest sense, infauna is any group of organisms that live in or on a different substrate than an animal. In this way, it is similar to epifaunal and endofaunal, which typically characterize animals living above and below, respectively, one other kind of organism. Infauna may be mainly aquatic (e.g., often benthic) or terrestrial (e.g., epiphytic).
Infauna is usually divided into five different categories:
- Aquatic infauna, which lives in water
- Terrestrial fauna that lives on and under the ground such as earthworms and other invertebrates.
- Epifaunal animals, which live on top of the substrate
- Endofaunal animals that live underneath the substrate.
- Subterranean infauna, which are terrestrial organisms living in natural and artificial underground environments
Some aquatic invertebrates such as crabs may be considered to be both epifaunal and infaunal. These are termed interstitial, meaning that their living space is in between the spaces of other organisms and they can move freely through those spaces. Other aquatic invertebrates such as many polychaete worms have a fauna benthic epifauna lifestyle, with infaunal members including oligochaetes, leeches, and other worms.
Aquatic terrestrial invertebrates are termed aquatic or amphibious insects – they have a benthic epifaunal lifestyle (e.g., water bugs) but may also live on land either permanently (as many ants do) or temporarily while mating for example.
Many epiphytic plants live in the infauna because they cannot survive on land. Similarly, many sea anemones are not considered to be epifaunal as their living space is water and sometimes gas bubble such that there is no substrate below them – but they still have a benthic lifestyle.
The most common members of this group are earthworms, which live in soil – often at least 20 cm deep and can be found everywhere on the surface of Earth’s continents and islands. Other invertebrates have a fauna benthica endofauna lifestyle including mollusks such as snails, slugs, and bivalves (e.g., clams), some insects such as beetles and spiders, nematodes worms of the order roundworms, and flatworm segmented creatures like earthworms.
This group includes any terrestrial organism that lives in natural or artificial underground environments – they can be found in caves, rock crevices, and abandoned mines. Subterranean infauna includes a range of invertebrates including cave-dwelling crustaceans such as shrimp, many species of tardigrades (aka water bears), millipedes, centipedes, and isopods which are often scavengers because there’s often not much food in caves.
Some who are interstitial creatures live both above and below the substrate, or seafloor for example. This can be advantageous to these organisms because they have a better chance of finding food by being able to navigate through different layers. Some animals such as earthworms may inhabit either endofauna (below) or epifauna (above) depending on the kind of environment.
Earthworms are a great example because they live in the soil, and can be considered endofaunal or epiphytic if you’re thinking about how they inhabit different layers. They may live below ground by digging into it to create tunnels for living spaces made up of the soil they use as a food source. They may also live on top of the ground, by crawling across it and creating tunnels in what we call worm casts, for protection from predators or to find new sources of food such as decomposing leaves.
What is the difference between infauna and Epifauna?
‘Epi’ is the term for any animal that lives on top of another organism. Infauna, meanwhile, refers to animals and plants found below the surface or at a specific depth in water; these are sometimes collectively referred to as benthos. Epifauna can also refer to organisms living on plants such as lichens and mosses.
Are crabs infauna or Epifauna?
Crabs live on land and are classified as epifauna.
The difference between infauna and ‘Epi’ is that the latter refers to animals living on top of another organism whereas the former applies to those below or at a specific depth in water, which can also include benthos (plants).