Neritic Zone: Definition, Animal Life, and Characteristics

Hawksbill turtle over coral reef
Hawksbill turtle swimming over coral reef with Golden butterflyfish and goldies.

Georgette Douwma / Getty Images

The neritic zone is the top ocean layer closest to the coastline and above the continental shelf. This zone extends from the intertidal zone (zone between high and low tide) to the edge of the continental shelf of the ocean floor, where the shelf drops off forming the continental slope. The neritic zone is shallow, reaching depths of about 200 meters (660 feet). It is a subsection of the pelagic zone and includes the ocean's epipelagic zone, which lies within the photic or light zone.

Key Takeaways: Neritic Zone

  • The neritic zone is the region of shallow water (200 meters depth) above the continental shelf where light penetrates to the sea floor.
  • Due to the abundant supply of sunlight and nutrients in this zone, it is the most productive ocean zone supporting the vast majority of marine life.
  • Regions within the neritic zone include the infralittoral zone, circalittoral zone, and subtidal zone.
  • Animal, protist, and plant life in the neritic zone include fish, crustaceans, mollusks, marine mammals, algae, kelp, and seagrass.

Neritic Zone Definition

From a marine biology perspective, the neritic zone, also referred to as the coastal ocean, is located in the photic or sunlight zone. The availability of sunlight in this region makes photosynthesis, which forms the basis of ocean ecosystems, possible. The neritic zone can be divided into biological zones based on the amount of light required to support life.

Ocean Zones
This image shows the ocean zones.  Encyclopaedia Britannica/UIG/Getty Images Plus

Infralittoral Zone

This region of shallow water in the neritic zone is closest to shore and below the low-water mark. There is ample light to allow for plant growth. In temperate environments, this region is typically dominated by large algae such as kelp.

Circalittoral Zone

This region of the neritic zone is deeper than the infralittoral zone. Many immobile organisms populate this zone, including sponges and bryozoans (aquatic animals living in colonies).

Subtidal Zone

Also called the sublittoral zone, this region of the neritic zone extends from the ocean floor near the shore to the edge of the continental shelf. The subtidal zone remains submerged and is home to algae, seagrasses, corals, crustaceans, and annelid worms.

From a physical oceanography perspective, the neritic zone experiences large-scale current movement that circulates nutrients in the region. Its boundaries extend from the intertidal zone to the continental shelf. The sublittoral zone is divided into inner and outer sublittoral zones. The inner sublittoral zone supports plant life that is attached to the seafloor, while the outer zone lacks attached plant life.

Physical Characteristics and Productivity

Coral reef scenery
Coral reef scenery with Red Sea bannerfish, golden butterflyfish, orange face or hooded butterflyfish, and lyretail anthias or goldies. Georgette Douwma / Photographer's Choice / Getty Images Plus

The neritic zone is the most productive ocean region, as it supports an abundance of living organisms. It has been estimated that 90% of the world's fish and shellfish harvest comes from the neritic zone. The stable environment of this zone provides light, oxygen, nutrients contributed by runoff from nearby land and up-welling from the continental shelf, as well as suitable salinity and temperature to support a wide range of marine life.

Abundant in these waters are photosynthetic protists called phytoplankton that support marine ecosystems by forming the basis of the food web. Phytoplankton are unicellular algae which use light from the sun to generate their own food and are themselves food for filter-feeders and zooplankton. Marine animals such as fish feed on zooplankton and fish in turn become food for other fish, marine mammals, birds, and humans. Marine bacteria also play an important role in the flow of trophic energy by decomposing organisms and recycling nutrients in the marine environment.

Animal Life

Shark and Sardines
This bronze whaler shark is swimming through a giant ball of sardines waiting to feed on them. wildestanimal / Moment / Getty Images

Animal life is truly abundant in the neritic zone. In tropical regions, coral reef ecosystems consisting of large colonies of corals are found. Coral reefs provide a home and protection for a multitude of marine animal species including fish, crustaceans, mollusks, worms, sponges, and invertebrate chordates. In temperate regions, kelp forest ecosystems support animals including anemones, star fish, sardines, sharks, and marine mammals such as seals, killer whales, sea lions, and sea otters.

Plant Life

Dugong and Cleaner Fish on Seagrass.
Dugong and Cleaner Fish on Seagrass. David Peart / arabianEye / Getty Images

Seagrass is a type of seaweed found in neritic marine environments. These angiosperms, or flowering plants, form grass bed underwater ecosystems that provide homes for fish, algae, nematodes, and other forms of marine life. Other marine animals such as turtles, manatees, dugong, sea urchin, and crabs feed off of these plants. Seagrass helps to stabilize the environment by preventing sediment erosion, producing oxygen, storing carbon, and removing pollutants. While seagrass seaweed is a true plant, other seaweed types such as kelp are not plants but algae.

Sources

  • Day, Trevor. Ecosystems Oceans. Routledge, 2014.
  • Garrison, Tom. Oceanography: an Invitation to Marine Science. Cengage Learning, 2015.
  • Jones, M. B., et al. Migrations and Dispersal of Marine Organisms: Proceedings of the 37th European Marine Biology Symposium Held in Reykjavik, Iceland, 5-9 August 2002. Springer Science & Business Media, 2013.
  • Karleskint, George, et al. Introduction to Marine Biology. 3rd ed., Cengage Learning, 2009.