What is the difference between subtidal and intertidal zones

Many intertidal animals can tolerate much greater temperature changes than their estuarine relatives. Possible adaptations are also light colors to reflect light or a large surface ribbed shells to dissipate heat. However, when cooled by evaporation, desiccation can lead to problems [14]. When the temperature is too low, the organisms must cope with physiological threats associated with cold stress. This can be the case in polar and temperate latitude coastal zones. The body fluids can then reach their freezing point and ice crystals develop.

This causes damage to cell membranes and increase of the osmotic concentration of the nonfrozen fluid. Some organisms have developed antifreeze proteins cryoprotectants. Increase of the concentration of osmolytes such as glycerol and sucrose in the body fluids increases the freezing tolerance [15].

Another strategy is to control formation and spread of internal ice crystals. When the ice formation is intracellular, it is lethal but extracellular ice formation can be tolerated.

Invertebrates found naturally in seawater of high salinity are more cold-tolerant than specimens inhabitating brackish waters.

In molluscs, the cold tolerance can be increased by acclimating the animals to higher salinities. This is probably based on increased concentrations of intracellular solutes such as amino acids [16].

Mobile organisms can avoid extreme temperatures by migrating to more suitable places; this is also a response to other stresses associated with emersion. Dehydration is the main environmental factor in the supralittoral and high intertidal zones, and the green macroalgae living in these zones are exposed regularly to air, yet still survive.

Dehydration-tolerance involves maintaining homeostasis during dehydration by minimizing or repairing any damage as fast as possible [17]. Highly mobile organisms can avoid the desiccation by migrating to a region that is more suitable. Less mobile organisms restrict various activities reduced metabolism and attach more firmly to the substrate.

Physiological features to tolerate water loss include adaptations such as: deployment of desiccation-resistant egg cases for embryonic development, reduction of the exposed surface areas across which water loss takes place thus accepting reduced gas exchange and concomitant anaerobic respiration with accumulation of metabolic end products , temporary depression in metabolic and developmental rates, maintenance of intracellular osmolytes for water retention and macromolecular protection and differential gene expression for the production of protective macromolecules [10].

Some sessile organisms can anticipate emersion by storing water in body cavities e. Many intertidal animals have a biological clock that allows them to anticipate changes as a result of tides circatidal rhythmicity or light circadian rhythmicity. Different signals play a role in the setting of endogenous rhythmicity in some crustaceans and crabs: water agitation, hydrostatic pressure, immersion, light and temperature cycles.

Once trained after a few tidal periods, the rhythmicity is maintained. Thanks to the biological clock, the animals can adapt in time, instead of waiting for an adverse situation to arise [18]. Sunlight is another parameter that influences the organisms. When there is too much sunlight, organisms dry out and the capacity to capture light energy can be weakened. The light that is not used or dissipated can cause damage to subcellular structures.

Algae can protect themselves against an excess of sunlight by so-called non-photochemical quenching NPQ : the light energy absorbed by the chlorophyll is dissipated in the form of heat or in the form of fluorescence.

NPQ is a quick and effective way to prevent damage from excess sunlight. There are also several other mechanisms, such as scavenging or deactivating free radicals produced from an excess of light [19]. Too little sunlight reduces the growth and reproduction of the organism, because photosynthesis is reduced. Intertidal zone organisms can be subjected to varying salinity, especially those living in pools that are not regularly refreshed with new seawater.

Rain can cause the salinity to drop and evaporation can cause the salinity to rise. Changes in salinity change the osmotic pressure in the cells of the body tissues, causing them to swell or shrink see Osmosis.

Organisms living in estuaries have adaptations to deal with this, such as adaptation of the cell membrane, salt storage in vacuoles or glands to secrete salt. However, most intertidal organisms are osmoconformers : they cannot control the salt content of their body.

In some species e. Most intertidal organisms adapt to salinity variations by producing organic osmolytes that keep intracellular fluids at the same pressure as the marine environment to avoid cell shrinkage or dilatation [21]. A wide variety of strategies to escape from predation exists.

The first strategy is calcification, which makes it more difficult for the predator to eat these organisms. This strategy is applied by algae. It makes them tougher and less nutritious. A second one is the production of chemicals, usually produced as secondary metabolites. These toxic chemicals can be produced all the time, but other chemicals are only produced in response to stimuli inducible defence. Another way to avoid predation is to have two distinct anatomical forms within one life cycle.

This can be e. Also the shape of the body can be a distinct evolutionary advantage. Bioluminescence is another strategy to avoid predators. Many intertidal and subtidal predators forage visually.

The light is used for warning, blinding, making scare, misleading or attracting the predator. A commonly used form of protection against predation is camouflage. This can be visually or chemically. Visual camouflage means that the prey becomes invisible to the predator by using the same colors as the environment. Chemical camouflage is the passive adsorption of chemicals. The predator does not smell the prey anymore, because the smell is masked. To escape seabird predation, some animals periwinkles, chitons and apex shells can hide in inaccessible crevasses or between seaweed.

Others, such as beach crabs, bury themselves in the sediments that often accumulate under rocks. One way to protect organisms from waves is permanent attachment. But this strategy cannot be used by organisms that have to move to feed themselves. These organisms make a compromise between mobility and attachment. Attachment can be done by different structures. Bivalves usually use threads byssal threads to attach to rocky surfaces or to other organisms, but they can also use a foot [22].

Another one is cementation. These animals take water into their bodies and filter out water-borne detritus and dissolved organic matter, and in turn provides the base of a food web that includes species such as sculpins, shrimps, flatfish and in the southern part of Glacier Bay and Icy Strait rockfish and greenlings. Current-scoured areas in the mid-bay area are considered prime real estate, as kelp and algae can grip the bottom and grow.

It is here you will find the greatest diversity of kelps and algae and these areas are especially known for being rich and productive feeding areas for marine life. Sedimentary marine basins of the mid-bay host major populations of king, Dungeness , and Tanner crabs, flatfishes, cods, and eelpouts on the bottom surface and large populations of worms and small crustaceans within the sediments.

Closer to the glaciers, less densely occupied communities are dominated by shrimps, smaller crustaceans, other arthropods, and worms. These invertebrates survive on nutrients transported to depth via a phenomenon called "marine snow. Thus sustained, crustaceans and the fishes that eat them survive and become a key prey base for seabirds and marine mammals throughout the year. Explore This Park. Info Alerts Maps Calendar Reserve.

Alerts In Effect Dismiss. Dismiss View all alerts. Glacier Bay Intertidal and Subtidal Zones. Intertidal Zone With tidal fluctuations as large as 25 vertical feet, Glacier Bay exhibits some of the largest tidal extremes in the world.

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