Intertidal Zone Characteristics | Intertidal Zone Animals & Plants Ecosystems

Intertidal Zone

What is Intertidal Zone ?

Intertidal zone refers to the area of the shoreline community that is above water at low tide and submerged at high tide. This zone includes both wet and dry areas. The wet coastal zone includes marshes, mangroves, lagoons, estuaries, and salt marshes.

The dry coastal zone includes sandy beaches, dunes, and cliff tops. The plants and animals of this area are uniquely adapted to the high and low tides that happen throughout the day.

The intertidal zone is vital to marine animals and plants due to the lack of terrestrial predators that inhabit the seafloor. The upper reaches of this shore zone are sometimes called splash zone or supralittoral fringe, while its lower edges are known as the subtidal or sublittoral fringe.

Tides are the primary driving force for the horizontal transport of material and organisms in or across the intertidal zone. The simplest effect is the tidal flow of water, which can transport small land animals, such as terrestrial snails, across large distances.

However, even larger animal forms, such as seals and even whales, can move across this zone with the right conditions. Tides may also exert local effects on materials by carrying floating materials into the air at high tide and dropping them when the water recedes. The intertidal zone is also the home of many animals and plants whose ranges include more than one tide zone.

The intertidal zone is formed by the coastline. It varies in size from a few meters wide to hundreds of kilometers long, depending on the shoreline’s characteristics (e.g., tidal amplitude, sediment types, wave exposure). The intertidal zone’s key characteristics include the presence of sunlight, freshwater, varying temperature, and salinity.

Types of Intertidal Zones

High Tide Zone

The high tide zone (also called the supralittoral zone) is usually covered with the intertidal zone. It is characterized by being exposed to air at low tide and covered by water at high tide. The high tide zone includes the splash or spray zone, which is always flooded when the tide is very high. In this area, exposed animals must avoid predation by terrestrial animals. The high tide zone is sparsely populated with only a few species, such as littorinids, gastropods, and barnacles.

Middle Tide Zone

The middle tide zone (also called the sublittoral zone) is the area that is exposed and then covered by water twice daily. In this region, there are two types of animals: those that are able to survive on land for extended periods of time (e.g., limpets) and those that are fully adapted to aquatic life (e.g., snails).

Low Tide Zone

The low tide zone (also called the subtidal zone) is the area that is exposed and then covered by water once daily. It is the area where tidal waves strike when the tide recedes. Pods of sponges and other hard zooids are numerous in this zone. The soft-bodied organisms initiate their development at high tide, undergo a diapause at low tide, and resume their high tide activities.

Intertidal Zone Characteristics

Intertidal Zone Ecosystem

The intertidal zone is the interface between the land and the ocean. Living organisms must be able to survive in both environments, but many different adaptations range from microscopic to large animals.

The two main factors in shaping this zone are the movement of sediment onshore and surficial processes (i.e., waves, currents, storms). Besides, there is a mix of other factors such as temperature variation, water availability, light availability, etc.

Light availability is an important regulator of the distribution and density of intertidal life, particularly in the high zone. The timing and duration of illumination are critical factors that affect species’ population density and size structure within a community.

Wave action also impacts the spatial distribution of organisms in this region. Tidal currents facilitate the transport of benthic organisms to new areas, thus promoting diffusion. These currents can be affected by wave action and other environmental factors.

Intertidal zone animals

Intertidal zone animals adaptations

The distribution of organisms in the intertidal zone is not random. A species may have a preferred temperature, salinity, substrate, wave action, or light exposure amount. This will determine the communities in different parts of the intertidal zone based on these preferences.

Some species may only live in certain parts due to their tolerance for less or higher water exposure. Other factors include predation, competition, and physical influences (e.g., exposure to current).

Intertidal organisms are exposed to numerous factors that affect them directly. The first factor is water temperature. Temperatures are measured by thermal dilution, which puts organisms into a bath of water to determine their preferred temperature range.

Changes in water temperature can positively or negatively affect the organism depending on the organism’s species and life-history stage. In addition to temperature, other abiotic factors may lead to changes in the distribution of organisms within this zone.

Salinity has been shown to be a key factor influencing intertidal distribution. Even though organisms can live in high salinity areas, they do not necessarily have to live within this zone.

The shoreline experiences seasonal changes in its wave action, storm frequency, and water level that may affect organisms’ distribution. Storms quickly move sediments about on the intertidal zone, burying intertidal organisms within a few hours. Most storms occur during an incoming tide, and it takes several hours for the sea level to return to its prior level.

Many intertidal organisms are affected by predation and competition from other organisms. Besides, most intertidal organisms are prey for fish at some point in their lives. Intertidal animals cannot rely on escaping predators by running away or hiding in vegetation because they are exposed to the open environment for the majority of their life cycle.

Intertidal organisms have adapted different ways to prevent predation, such as defensive coloration, camouflage, escape behavior, and the use of warning coloration. Size may also play a role in predation in this zone. A smaller size is thought to be an adaptation that allows organisms to avoid predation by burrowing or being able to move more quickly.

The intertidal zone is a highly dynamic environment where waves, currents, temperature fluctuations, salinity change, and sediment movements affect living organisms within the community. The abiotic factors of the coastline account for many of these changes directly or indirectly.

Organisms must be able to survive in this environment but also reach their adult life stage. They must develop a tolerance for certain abiotic factors or have adaptations to change with the fluctuating environment.

The intertidal zone is a highly productive region of beach, seabed, and nearshore waters and forms the transition between terrestrial and marine ecosystems. The zone supports large biodiversity because of its dynamic nature.

It is also home to many organisms that depend on the biogeochemical cycles of carbon and nutrients within the water column. Intertidal organisms are dependent on both the nitrogen cycle and the carbon cycle of the intertidal zone.

The intertidal zone is an important habitat for many organisms that cannot survive in other environments. It provides habitat for species that can only live in specific areas, such as gastropods and bivalves, as well as species that are sessile and cannot move or fight off predators.

These organisms rely on other organisms to take on these duties for them. The intertidal zone’s different abiotic factors also ensure that at least one organism within the community can survive in adverse conditions.

Intertidal organisms are affected by factors such as predation, competition for food and space, and changes in temperature, salinity, and light. Many organisms have adapted to survive in these conditions through camouflage, escape behavior, or the use of warning coloration.

Light is important in this environment because it increases photosynthetic organisms’ growth rate, which is highly dependent on light intensity for their photosynthesis.

Intertidal organisms which take refuge in the intertidal zone are exposed to high levels of UV-B radiation. These organisms have evolved mechanisms to deal with these changes, such as the protective mechanisms offered by the intertidal seaweed “Fucus distichus.”

The effects of temperature and salinity can depend on whether the organism lives on the shore or in the water column and their tolerance for variations in these factors.

Studies on intertidal communities have grown in popularity because of the practical applications they have in sustainable management and conservation. An understanding of how organisms interact within these communities can help in the design of marine protected areas.

Since most marine organisms are sessile, their survival depends on other organisms within a community to carry out predator or competitor exclusion and ensure sufficient food supplies exist. The animal species that live in this environment must be equally adapted to cope with exposure to extreme environmental changes.

Intertidal communities have been used in studies to understand the role of each species affected by environmental variables. Some species are more resistant to environmental changes or are generalists and can cope with a variety of factors such as temperature and salinity. Other types of species are more specific and sensitive to their environment.

Examples of these types of organisms include “Gastropods” (such as limpets, sea hares, snails), “Horseshoe limpets,” and sponges.

Intertidal Zone Diagram

Intertidal zone Plants

Intertidal Zone Plants Adaptations

Unlike most plants, Intertidal zone plants are able to withstand salty water, harsh conditions, and ocean storms. Those who survive in this environment are often tougher, willowy, and have different adaptations to withstand these harsh conditions.

They have a variety of adaptations that include salt excretion, protective coverings on leaves, and air-filled bladders.

These plants are in an environment where the tides are higher than the plants. They usually have a foothold or a root system that can withstand the higher tides. These plants are mainly found in the water level zone of the beach.  In this zone, plants tend to be less flowering plants with leaves and more salty plants with adaptations to help them withstand the salt because of the high salinity.

Examples of Intertidal Zone Plants: Sea urchins, kelp, sea anemones, and other marine plants are commonly found living in the intertidal zone.

Intertidal Zone Salinity

Salinity can change dramatically due to temperatures or weather. Normal ocean salinity is around 33-35 ppt, and Estuarine salinity normally varies between 5 ppt and 30 ppt.

Organisms in the intertidal are normally euryhaline (can tolerate a wide variety of salinities); subtidal organisms, by contrast, are normally stenohaline (tolerate a very low range of salinities).

Salinity may begin at 20-25 ppt and climb dramatically during the day due to water loss when the intertidal is exposed. Salinity may also drop during the day due to a sudden influx of freshwater provided by a passing thunderstorm.

Now, imagine a salinity change of possibly 20 ppt or more combined with a temperature change of 40 degrees or more. Organisms must be extremely adaptable or perish.

Intertidal Zone Depth

The intertidal zone is often exposed to the effects of tidal and longshore currents and breaking waves, to a depth of 5 to 10 meters (16 to 33 feet) below the low-tide level, depending on the strength of storm waves.

The Bay of Fundy in southeastern Canada has the world’s largest tidal differential, with a 65-foot (20-meter) difference between high and low tides. The bay has distinct features that allow for these high tides.

The Bay of Fundy is very deep and therefore holds a huge volume of water, and the bay’s peculiar shape allows the water to oscillate (swing back and forth) for 12 to 13 hours. Every 12 hours and 26 minutes, the oscillation cycle coincides with the high tide on the Atlantic Ocean, causing the water in the bay to resonate.

Note: 

Intertidal zone depth: The water body leaves the shallow water and reaches the depth where it starts to expose itself to wave action.

Intertidal zone width: The intertidal zone extends across a tidal shore’s width, from low water mark to high watermark. The distance between high and low tide is called an intertidal area.

Low tide: Low tide is just before the rise of neap tides, when tidal waters are exposed at their lowest level, usually exposing soft-bodied organisms like mussels and limpets.

Rocky intertidal zone

A rocky shore is a shore that is made up of rock rather than sand or sediment. Rocky shores are found in tropical and sub-tropical coastlines around the world. They support unique ecosystems not found in dune systems or coral reefs.

The Pacific coast of Mexico has rocky shores with a diversity of habitats, including algal zones, sandy, estuarine areas, and mangrove forests. The range extends south to the Isthmus of Tehuantepec and the Gulf Coast of Mexico.

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