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What the tide is and why it occurs
The tide is the movement of long period waves of water throughout the ocean. There are multiple different types of tides such as low tide, high tide, and spring and neap tides, which all refer to the water level as the tides occur. High tide occurs when the water level rises and reaches its highest point, while low tide occurs when the water level decreases and reaches its lowest point. Spring tides occur when the sun, earth, and moon line up, this causes constructive interference which means the high tides are at the highest they can be while the low tides are at their lowest. Neap tides occur when the moon is perpendicular, or at a 90° angle, this causes destructive interference which means the high tide is as its lowest point while the low tide is at its highest.

The tides occur due to forces that the moon and the sun exert on earth. One of these forces is gravitational force, which is caused by the attraction between the earth and the sun or moon. The moon has stronger gravitational forces since it is closer to the earth. Another of these forces is centrifugal force which is the force created by the outward push caused by the rotation of the earth and moon around each other.

How the tide is useful for people?
The tides are used by people in a multitude of different ways.

Fishing:
One way is through fishing. People watch how the tides affect the movement and location of fish in order to determine the best possible fishing locations and times. Fish reproduction is also affected by the tides which is seen in capelin, people have been able to use this to their advantage in order to make fishing more efficient.

Recreation:
The waves created by tides are used by many while swimming, boating, surfing, rafting, and much more. Tidal bores are a phenomenon that are highly useful in this area. Tidal bores are caused when water is pushed towards the land by the tide and flows up a river or another gradually narrowing opening, this narrowing causes the waves found in such areas to be very large and helpful for those that surf or raft.

Power:
Using the tide to create power results in a large scale, clean, renewable way to generate power. Since the tides occur at roughly the same time daily, are highly predictable, and always flows in the same direction, they can be much more efficient than other types of power, like wind. Some places on earth, like along the Australian coast, the tides are semidiurnal, which means high and low tide both occur twice a day, making tidal power in these areas even more efficient.

High Tide Flooding:
Areas with rising sea levels or high sea level variability experience flooding during high tide. This flooding causes damage to coastal ecosystems, affecting both plants and animals in the area, as well as any humans or manmade infrastructure in the area.

Intertidal zone
The intertidal zone is an ecosystem found on marine shorelines and is the area between the high tide and low tide that inhabits variety of organisms.

Challenges of intertidal zones:
The intertidal zone is a physiologically challenging habitat for residents due to the persistent, tide-driven variations in abiotic (such as temperature, oxygen, and salinity) and biotic (such as food supply and predation) conditions. Organisms that live in the intertidal zones, have developed adaptation to overcome the fluctuations between being submerged in water as opposed to being exposed to air.

Desiccation:
Some organisms may become exposed to air during the time of low tide, and as a result become a subject of desiccation. Some organisms hide and take shelter within the moist cracks of the rocks like crabs. Some other organisms create home scars. Home scars are wears in the rock fitting the organism's body size and shape, this helps organisms avoid evaporation by their shells facing the sun and also to trap water inside the scar. Other organisms such as mussels close up their shells to decrease water loss. Another strategy is to live in tightly packed groups to decrease the surface area of individuals that is exposed to air and this evaporation.

Temperature stress:
Heat stress is another challenge for organisms living in the intertidal zones as a result of exposure to sun radiation and air during low tide. One strategy to tolerate this condition is the adaption of rough, uneven and light-colored shells. These characteristics will help organism to reflect the solar radiation as much as possible. In contrast, in higher latitudes, organisms tend to develop smooth and dark colored shells in order to absorb more solar radiation to tolerate the colder temperatures. Another strategy observed in intertidal zones is to hang from rocks or other surfaces. By hanging in the middle of air, organism allows airflow around its body in order to cool down in warm temperatures. Heat shock proteins are an alternative way to reduce heat shock. Heat shock proteins act as chaperons and allow proteins to be correctly folded into 3D structures in higher temperatures.

Wave action:
When waves break onto shoreline, the transfer hydrodynamic forces onto intertidal organisms. As a result, organisms living in the intertidal zones have evolved thick shells, that are usually flattened and fixed into the rocks or other surfaces in order to decrease damages caused by wave actions.

Low oxygen levels:
Non-air breathers:

Organisms of intertidal zones might find it challenging to absorbs oxygen at the time of low tide as they use diffusion to take up oxygen when submerged. Most organisms evolved the ability to use anaerobic respiration mechanisms to survive. Furthermore, intertidal organisms tend to have higher amounts of antioxidant enzymes to lower the amount of reactive oxygen species and by-products.

Air breathers:

Some organisms have developed unusual traits to tolerate low oxygen levels. An example would be the air breathing fish in rock pools. Clinocottus analis also known as Woolly sculpin, is an example of air breathing fish found in tide pools. These organisms are able to transport oxygen via their skin or gills when they go to the water surface. They have also evolved mucus on body surface to reduce water loss as they go to water surface, in addition to large pectoral fins to aid them in emerging from water.

Changes in salinity:
Another challenge of intertidal environments is the change in salinity in organism's media. Some animals like mussels close their shells to avoid this problem, while other organisms have strategies to regulate salinity via osmoregulation. These strategies include changes in free amino acid concentrations, using ATP driven ion channels and using symbionts for regulation. The Giant Green Anemone is an example of organisms that uses a symbiont for salinity regulation.

Sea turtles:
Sea turtles make use of the intertidal zone by laying their eggs above the highest high tide point. This allows the eggs to be protected under the sand while also ensuring the water at high tide doesn't move the sand and expose the eggs. Baby turtles also use the tide by hatching when high tide occurs so that the water flowing back out to sea carries the baby turtles faster then would be able if they had to crawl all the way to the water at any other time.

Birds:
In the intertidal zone during low tide there are many small pockets of water mixed into the land that becomes dry at this time. Some birds; such as seagulls, eagles, and flamingos, use this to their advantage by timing their hunting/feeding times to ensure they are being as efficient as possible. The prey are more exposed, which allows the birds to feed without having to dive in the water or search for food.