The intertidal zone is the area on a beach situated between the high tide and the low tide. This zone often includes more than one habitat, including wetlands and rocky cliffs. The intertidal zone provides habitat to a variety of animal species, such as mollusks, crustaceans, worms, some species of coral and algae. The intertidal zone can be as wide as a sandy beach several meters wide or a narrow as a steeped rocky cliff. Organisms have learned to adapt to the water level fluctuations caused by the daily tides, water turbulence, changing temperature, moisture and salinity.
The intertidal zone
Typically, an intertidal rocky shore comprises a splash zone (supratidal zone), which is the region that is repeatedly splashed by the action of waves. Along the shoreline of most beaches, the intertidal zone is usually divided into three main zones; low intertidal zone, which is exposed to the atmosphere each time a low tide recedes; middle intertidal zone, which is regularly exposed and flooded by the action of ocean tides; and the high intertidal zone, which is only submerged under sea water by high tides; however, this zone remains most of the time exposed to the land environment.
Intertidal zone stressors
The intertidal zone is continuously subjected to the influence of natural environmental factors which put the organisms thriving there at tremendous stress, so these organisms have developed ways to adapt in this harsh environment. During the course of one day, the intertidal zone is affected by two lows and two high tides, producing turbulence and drag each time a high tide recedes. During low tides, organisms are exposed to the air, higher temperatures and salinity, risking desiccation. In order to survive these stressing conditions, intertidal organisms have developed ingenious ways to cope with it.
Intertidal organisms, especially those living at the outer limits of the intertidal zone (high intertidal) are subjected to varied temperature changes. While they remain under water, the temperature may fluctuate by a few degrees; however, during a low tide, temperatures may vary from freezing to hot, depending on the season. Snails and crabs feed during high tides; however, during a low tide, they burrow under moist holes in the sand. Other organisms may develop either a dark or light colored shell to regulate temperature.
Many intertidal organisms will dry out or desiccate when exposed to the air and sunlight during a low tide. Snails avoid desiccation and water loss by hiding totally into their shells. Limpets live in home scars attached to hard substrates. They leave the scar for grazing and return just before the tide recedes. Some develop an outer shell or mucus membrane to shield their bodies and prevent desiccation. Some species of algae that are subjected to long periods of desiccation are able to rehydrate and recover. Barnacles and mussels attach themselves to rocks to avoid being washed away.
Some plants, such as those living in salt marshes, prevent salt uptake by secreting salt through their glands. High salinity concentrations usually occur at those locations with high salinity rates, such as intertidal pools and salt marshes. The salinity in tide pools may vary when the water contained in it is diluted by rain, affecting some fish like blennies and sculpin. Shading by some plants may slow evaporation in certain areas of the intertidal zone, reducing salinity. Sea stars, and echinoderms are intolerant to low salinities and their metabolism is unable to perform osmoregulation.
Intertidal organisms must protect from being washed away by the force of waves. Some mollusks, such as limpets, possess hard conical shells that protect them from high wave action. Sea stars have various suctioning feet used to attach themselves to hard substrates. Kelps can grow from 20-45 meters (66-148 ft.) long. They possess a holdfast with a root-like haptera, which attaches the kelp to the ocean floor, protecting it from the waves. The intertidal zone is washed everyday by the action of sea waves, and the organisms thriving there have adapted to deal with changes in temperature, moisture, turbulence, desiccation and salinity.