The neritic zone is the part of the pelagic environment that is located on the continental shelf. The latter is the shallowest part of the continental margin and extends from the lowest point of low tide to approximately 200 meters deep.
This zone corresponds to the so-called sub-littoral zone or the coastal zone of the epipelagic province. It is also linked to the photic zone, which indicates that the neritic province extends as far as sunlight can reach the seabed.
Divisions of the ocean, photic zone. Taken and edited from: Oceanic divisions.svg: Chris huh.
It is an area of high primary productivity due to the photosynthetic activity of phytoplankton, macroalgae and seagrasses that develop in it. This productivity is sustained mainly by nutrients that are transported from land by rivers and rains.
characteristics
This area extends from the lowest point of low tide to 200 meters deep, which means that it is always submerged under water.
It is a well-lit area and generally the sun's rays can reach the seabed.
The environmental conditions in this area are quite stable, although the water temperature depends on the latitude where it is located, it is maintained more or less in each area in question.
The waters of the neritic zones are generally rich in nutrients due to carry-overs from the terrestrial zone by means of rivers and runoff waters. Coastal upwelling or upwelling also contributes to this nutrient richness.
The neritic zone is the most productive area of the marine areas. Some researchers have estimated that more than 90% of the organisms caught worldwide come from this zone.
Flora
The flora of the neritic zone is represented by the photosynthetic species that inhabit the water column (pelagic), as well as those that inhabit the seabed (benthic). The former are dominated by phytoplankton, while the latter are by macroalgae and sea grasses (phanerogams)
Phytoplankton
Phytoplankton diversity. Taken and edited from: Prof. Gordon T. Taylor, Stony Brook University, via Wikimedia Commons.
It is mainly made up of unicellular algae and photosynthetic bacteria. It is the main responsible for primary production in the neritic environment, with a contribution close to 80% of the total primary production in this area.
Among the main components of neritic phytoplankton are cyanobacteria, dinoflagellates and also diatoms. Cyanobacteria are prokaryotic organisms endowed with chlorophyll a and phycocyanin, a blue pigment that gives cells that color and is also responsible for the old name of the group (cyanophytes or blue algae).
Diatoms are unicellular algae that are covered by a pair of valves of unequal size, the upper or epitheca is smaller in size and fits into the lower or mortgage, which is larger.
Dinoflagellates, dinofitos or also called peridineals are the most important representatives of phytoplankton behind diatoms. They may or may not be protected by a structure called teak, which is cellulosic in nature. They are characterized by presenting two flagella arranged perpendicular to one another.
Dinoflagellates in particular environmental conditions can present exponential population growth and produce massive outcrops known as red tides.
Macroalgae
Macroalgae belong to three distinct groups known as green, red, and brown algae. They are located clinging to the substrate using different structures, such as rhizoids
Green algae belong to the phylum Chlorophyta, characterized in that they contain chlorophylls and they store starch. In addition to representatives within the macroalgae, this phylum also has representatives among the microalgae. An example of chlorophyte macroalgae is the members of the Enteromorpha and Ulva genera.
Red algae, or Rhodophytas, are algae that lack flagellate cells, possess chlorophyll a and d and accessory pigments such as α and β-carotenes, xanthophyll, zeaxanthin, lutein and phycobiliproteins. They are predominantly filamentous, but there are also foliaceous-looking parenchymal forms.
These algae present their highest abundance of species in the tropical zone, decreasing considerably towards the temperate zones.
The phylum Heterokonthophyta (class Phaeophyceae) contains brown algae. These have their characteristic coloration thanks to the large amounts of fucoxanthin in their chloroplasts. In addition, these algae contain chlorophylls a, c 1 and c 2.
Seagrasses
They are a group of phanerogams that grow in the benthos and resemble the grasslands of the terrestrial environment, among the main species of this group are the Thalassia, Zostera and also Posidonia.
Fauna
Neritic fauna is very diverse, harboring representatives of practically all existing animal phyla.
Zooplankton
It is a heterogeneous group of heterotrophic organisms that move at the mercy of the marine currents and contains from microscopic animals to large jellyfish with an umbrella diameter of more than one meter. Virtually all animal groups have representatives who spend at least one stage of their life as members of plankton.
The main representatives of this group of organisms are copepods, small crustaceans that have a body divided into a head or cephalosome and a body or metasome. Copepods are present in great numbers in all seas as well as at all times of the year.
Pteropods (mollusks), ketognaths, rotifers, some polychaetes and the larvae of numerous species of fish are also part of the plankton.
Necton
Nekton organism, whale shark, Rhincodon typus. Taken and edited from: Tilonaut, via Wikimedia Commons.
Nekton are made up of pelagic organisms that are capable of actively swimming opposing or overcoming currents and waves. This group includes organisms as diverse as pelagic fish (herring, mullet, tuna, among others), cephalopod molluscs (squid), reptiles (sea turtles) and mammals (dolphins).
Benthic fauna
The benthic fauna is the fauna that is associated with the seabed. In this case, to the bottoms of the neritic zone. Among the littoral benthic animals, there are, for example, a great variety of sponges, echinoderms (sea cucumbers, sea spiders, regular and irregular urchins), crabs, shrimp, anemones, corals, sea squirts or snails, among others.
Biodiversity of the photic zone, coral reefs. Taken and edited from: Wise Hok Wai Lum.
There are also numerous species of benthic fish in the neritic zone, such as frogfish, rays, moray eels, conger eels and sole. The latter have undergone a great bodily change as a mechanism of adaptation to benthic life.
These fish have a laterally compressed body and rest on the seabed on one side, while the eye on the "lower" side of the body has moved, leaving both eyes on the same side of the body.
References
- G. Cognetti, M. Sará & G. Magazzú (2001). Marine biology. Editorial Ariel.
- G. Huber (2007). Marine Biology. 6 th edition. The McGraw-Hill Companies, Inc.
- Neritic zone. On Wikipedia. Recovered from: en.wikipedia.org.
- Adaptations of animals in the neritic zone. Recovered from: es. Scienceaq.com.
- R. Barnes, D. Cushing, H. Elderfield, A. Fleet, B. Funnell, D. Grahams, P. Liss, I. McCave, J. Pearce, P. Smith, S. Smith & C. Vicent (1978). Oceanography. Biological Enviroment. Unit 9 The pelagic system; Unit 10 The Benthic system. The Open University.
- F. Lozano. Oceanography, marine biology and fishing. Volume I. Auditorium.