Intertidal Zone Temperature Change

Once students have explored interactions between living things on the rocky shore and the adaptations those living things have, students focus on the nonliving, or abiotic, parts of a rocky shore environment. Students explore how the different levels of the intertidal zone change in temperature from day to night to analyze which organisms are best suited for life in each zone.

• Organisms don’t only need adaptations to help them survive their interactions with other living things; they also need them to help them survive the conditions of the environment.
• Rocky shores are harsh environments in which to live because organisms must be able to tolerate a high level of environmental stress.
• As the sun shines, it transfers light and heat energy to Earth’s surface. However, each surface absorbs and reflects different amounts of energy, and so warms up and cools down at different rates.

• Why are rocky shores such harsh environments?
• Why are there “zones,” or layers, in the intertidal zone?
• How would you describe the environment of the splash zone?
• How would you describe the environment of the high intertidal zone?
• How is radiation different from the other two forms of heat transfer (conduction and convection)?
• How is heat transferred within a substance like sand or rock once its surface is warmed by the sun?
• Why does the ocean remain warmer in the winter and cooler in the summer than the land does?
• What are some environmental stresses on surfaces that become really hot or cold very quickly?

Desiccation : drying due to the removal of water

High tide : the point when seawater rises to its highest level during a tide cycle

Low tide : the point when seawater retreats to its lowest level during a tide cycle

Stress : any factor that reduces the ability of an organism to survive

Tide : the alternating rise and fall of the sea with respect to land

Drying Out by Radiation

As the tide on a rocky shore slowly drops, the shore becomes exposed to the air. The farther up the intertidal zone is, the more exposure an organism faces. Remember that the intertidal zone is the region of land that is covered and uncovered by water between high and low tides. Organisms that spend most of their time on the exposed rocks face many challenges. One challenge is desiccation. Desiccation is drying out due to the removal of water. Another challenge is extreme temperature changes.

Most organisms cannot function in extremely high temperatures. Some survive by moving under rocks during the hottest times of the day. This lets them avoid the heat and dryness of exposed air. For example, many snails and crabs crawl around searching for food during high tide. They then hide under rocks at low tide. Their shells also shelter them from high temperatures and hold water to keep the animals from drying out.

Radiation

The exposed shoreline is a harsh environment because the sun releases a huge amount of energy. This light energy reaches Earth’s surface by radiation, which is the only form of heat transfer that occurs without contact between the heat source and the object heated.

The amount of solar radiation differs throughout the year. It also changes from day to night. This is why it’s colder in winter and at night than it is in the summer and during the day. Some materials also absorb different amounts of energy. For example, water responds to temperature change much more slowly than land does. This is because the ocean has a higher heat capacity than land. Heat capacity is the energy required to raise the temperature. In other words, it takes longer for water to heat and cool than the land. As the sun heats Earth, the land becomes warmer before the ocean does because the ocean has a higher heat capacity.

Conduction and Convection

Once the sun’s energy hits Earth’s surface, it can be transferred to other substances through conduction or convection. Conduction is a form of heat transfer that occurs when molecules collide. When two substances that have different temperatures come into contact with each other, the faster-moving molecules of the warmer object give up some of their energy to the slower molecules when they come into contact with one another. The slower molecules gain more energy. This makes them start to move faster. Heat always flows in this direction, transferring out of hotter regions or objects and into colder ones.

Adaptations to Reduce Heat Transfer

Some rocky shore organisms have adaptations that help them reduce the amount of heat transfer that occurs between them and the rocks. For example, many marine snails produce a mucus around their shells. This mucus acts as a protective barrier when they are exposed to the air. This mucus helps to insulate the snails so that heat from the rocks doesn’t transfer to them. Good thermal insulators do not easily let heat pass through them.

Marine snails produce a mucus that acts as an insulator, reducing heat transfer from the rocks. Water is also a thermal insulator because it doesn’t conduct heat well. Air is another natural thermal. Feathers, fur, and natural fibers are all thermal insulators, helping different animals regulate their temperature so too much heat doesn’t transfer into or out of their bodies. Human-made insulators include plastics and foams.

Rocky Shore Zones

If you’ve ever walked along a rocky shore, you may have noticed something that has long fascinated ecologists. The shoreline appears layered as you move from the rocks to the water. Each layer has a completely different set of organisms living there.

Each layer is made up of different numbers and kinds of organisms depending on how much it is exposed to air and water. There are four main levels: the splash zone, the high intertidal zone, the mid- intertidal zone, and the low intertidal zone.

Nonliving parts of an ecosystem are called abiotic factors. These include air, water, and sunlight. Scientists believe that in general, the abiotic stresses of the environment determine how far up the rocks a species can live. These stresses include extreme temperatures and the risk of desiccation. For example, mussels cannot live farther up the rocks than they do because of the nonliving stresses of temperature extremes and desiccation.

The living stresses of the environment determine how close to the water a species can live. These stresses include predation and competition. Remember how sea stars act as checks on mussels? Scientists have found that the lower boundary of where mussels live is just beyond where sea stars can live.

Because of environmental stresses and predation, mussels are typically found in the mid-intertidal zone. This zone is covered by seawater for approximately the same amount of time it is exposed to air. Tide pools are often seen in the mid-intertidal zone.

Many different kinds of organisms live in the mid-intertidal zone. Barnacles are similar to mussels. They glue themselves to a surface so they do not get tossed around by waves. They also are covered by shells that they seal shut when the tide goes out to minimize water loss. When the tide comes in again, they open their shells because they, like mussels, are filter feeders so they gather energy by straining nutrients and small organisms out of the water.

The most diverse zone is the low intertidal zone. This zone is nearly always covered in seawater, so it is teeming with life. There is much more vegetation, particularly seaweeds. Organisms that live here generally are not adapted to dryness or extreme temperatures. Sea stars are common here. Tube worms, sea urchins, snails, anemones, and different kinds of algae are also common. Kelp is one type of brown algae that grows in long strands from the seafloor. Instead of roots, kelp have special structures called holdfasts. Holdfasts cling to surfaces even in rough waters. Kelp stay standing in the water using air- filled sacs called gas bladders that act like inflatable swimwear.

The least diverse zone is the splash zone. This is the area above where the highest tide reaches. This zone is regularly splashed by waves but is rarely covered by water. Very few organisms live in this ecosystem because of the harsh conditions. Those that do must endure the drying heat of the sun in the summer and extremely low temperatures in the winter.

The high intertidal zone is somewhat more diverse than the splash zone, but not by much. This zone is only covered by seawater at high tide. As a result, it is very salty because salt water evaporates, leaving behind salt deposits. Some plants are able to survive here, but not many. Organisms that make their home here have adaptations that allow them to survive extreme temperatures, changes in moisture availability, and high salinity.

In this lesson, students explore the phenomena of extreme temperatures in the intertidal zone by designing an experiment to examine the relationship between the substances that make up each intertidal zone level and how those substances change in temperature from day to night. Students collect and analyze data on the temperature of different levels of the intertidal zone to determine the relationship between energy transfer, the kind of material, and the change in particle motion of the material.