BENTHOS: CHARACTERISTICS, NUTRITION AND EXAMPLES OF ORGANISMS - BIOLOGY - 2025

The term benthos is used to define the communities of organisms that live at the bottom of aquatic environments. This term began to be used at the end of the 19th century and comes from the Greek “βένθος” or benthos, which means seabed.

Although the word benthos refers to the seabed, it is also used for freshwater and estuarine ecosystems. Benthic communities can be composed of an immense variety of species, such as those of coral reefs.

Corals and other benthic reef organisms. Taken and edited from US Fish & Wildlife Service - Pacific Region's, via Wikimedia Commons.

They can also be not very diverse, such as the benthic communities of the abyssal areas. Many species of benthos are of high interest in fisheries, such as some shrimp species, others have biomedical importance.

The organisms that inhabit the benthos are called benthic, an ecological term that lacks taxonomic validity. These communities are made up of a great diversity of species. In the benthos can be found from microscopic organisms to seagrass and fish.

Benthic zone

The benthic zone covers all the bottoms of bodies of water, be they marine, freshwater or estuarine. The depth at which these funds are found is highly variable. They can go from the tidal zones, which are eventually exposed, to more than 6 thousand meters (hadal zone) in depth.

Benthic or benthic zones can be composed of rocky substrates, coral reefs, sandy and muddy bottoms, they can also consist of seagrass meadows.

General characteristics

Community of benthos at an abyssal depth in the islands of Hawaii. Taken and edited from NOAA Photo Library, via Wikimedia Commons.

Almost all known taxa or organism taxa have representatives in the benthos. The common characteristic of all is that they live associated with the fund. These organisms have evolved in such a way that they present a great variety of adaptations for this type of environment.

Some characteristics shared by different taxa of benthic organisms include:

-They can be completely sessile, for which they develop structures that allow them to adhere to the substrate. An example of these structures are rhizoids (algae), fixation discs (algae, anemones), sucker species (mollusks), cement glands (crustaceans, mollusks), among others.

-They can form colonies, which can be reduced in size (for example some species of ascidians) or acquire large dimensions (coral reefs).

-They have developed a great variety of structures that allow them to move along the bottom. Among these structures are pseudopodia (protists), legs with sharp nails (crustaceans), fins (fish), tube feet (echinoderms), among others.

-Its body shape was modified to better adapt to the substrate, flattening or depressing. For example, sole, marine rays and starfish.

-Finally, they have developed a great variety of ecological relationships, such as parasitism, symbiosis, mutualism, amensalism, among others.

-Benthos organisms come in a wide range of sizes. According to their size, they can be classified into macrobenthos (greater than one millimeter), meiobenthos (less than one millimeter but greater than 32 microns) and microbenthos (organisms smaller than 32 microns).

-Benthos animals can live on top of the substrate (epifauna), or within the substrate (infauna). Fish that live in the water column, but near the bottom and not directly above it, are called demersal.

Nutrition

The nutrition or feeding of the benthic organisms depends on many biotic and abiotic factors. Biotic factors include the relationships of complex food webs and the individuals that compose them.

On the other hand, abiotic factors such as availability of light, depth, salinity and even temperature, influence photosynthetic and chemosynthetic communities and those that feed on them.

Autotrophs and Chemotrophs

They are organisms that produce their own food or nutrients using sunlight (photosynthetic autotrophs) or through the synthesis of chemical compounds (chemotrophs). For example, seagrass beds (autotrophs) and methanotrophic bacteria that can live associated with mussels (chemotrophs).

Heterotrophs

Heterotrophs are those organisms that cannot synthesize their own food, therefore they require another or other organisms to obtain it. Heterotrophic feeding can be divided, in a general way, into:

Herbivorous

Herbivores are those organisms that feed exclusively on organisms of the plant kingdom. In the case of benthos, they can feed on varieties of algae, aquatic phanerogams, colonies of microalgae and other plant forms. For example, chitons and some species of spider crabs.

Carnivorous

Organisms that feed on other animals, commonly called predators. These organisms include a wide variety of fish, such as groupers and snappers, blue crabs (portunidae) and starfish.

Omnivora

Individuals capable of feeding on plants or algae as well as animals. Many benthos animals have developed mixed eating habits. Examples of this are some fish, as well as some snails and crabs.

Ghouls or scavengers

Scavengers are individuals that feed on dead or decomposing animals. In the case of benthic scavengers, the remains of food and dead organisms from the benthic and pelagic environment (upper zone of the water column) that are deposited on the bottoms.

Examples of benthic organisms

Bacteria

Benthic communities contain a wide variety of bacteria. Aerobic, anaerobic and facultative bacteria have been identified in different benthic environments. Bacteria play a fundamental role in these environments, as they are part of many biological and chemical cycles.

Algae

The communities of algae associated with benthic substrates include almost all the large taxonomic groups, such as chlorophytes (green algae), rhodophytes (red algae) and phaeophytes (brown algae).

The morphology of these algae and the type of life they lead is quite diverse. An example of this are some algae that are epiphytes (live on top of) other algae, while others live on rocky bottoms, and others on muddy bottoms.

Phanerogams

Seagrass meadows are very important, as they are one of the most productive ecosystems. In addition to this, these meadows also protect coastal areas from erosion by waves, and because they are CO2 sinks.

Invertebrates

Invertebrates are a vast group of organisms made up of more than 30 phyla. Benthic communities can host large numbers of these phyla.

One of the most representative invertebrates of benthic communities are corals, which are capable of forming reefs that extend for kilometers, such as the Great Australian Barrier Reef. These structures provide shelter and food for a practically incalculable variety of organisms, both plants and animals.

Other examples of benthic invertebrates are sponges (porifers), anemones (cnidarians), fireworms (annelids), crabs, shrimp, lobsters (crustaceans), snails, clams, octopuses (mollusks), starfish, urchins and also sea cucumbers (echinoderms).

Vertebrates

Fish are the dominant vertebrates in the benthos. These organisms have developed adaptations to the environment, such as depressed bodies characteristic of stripes and compressed bodies like that of sole.

Other adaptations are the pectoral fins, which in some species of chimera sharks make it appear that they are walking on the bottom.

Sole fish of the Soleidae family. Taken and edited from: Sébastien Vasquez, via Wikimedia Commons.

References

1. Benthic algae. Ecured. Recovered from ecured.cu.
2. Benthos. Marine Research Findings of the VECTORS Project. Recovered from marine-vectors.eu.
3. CP Hickman, LS Roberts & A. Larson (1997). Integrated principles of zoology. Boston, Mass: WCB / McGraw-Hill.
4. EE Ruppert, RD Barnes & RD Barnes (1994). Invertebrate zoology. Fort Worth: Saunders College Pub.
5. Benthic Fish. A Dictionary of Ecology. Recovered from encyclopedia.com.
6. CR Nichols & RG Williams (2009). Encyclopedia of Marine Science. Facts On File, Inc.