Rocky Shore Ecosystems

The science background provides teachers with more in-depth information on the phenomena students explore. Below is an excerpt from the science background section on rocky shore ecosystems.

Rocky Shore Ecosystems

Rocky shores are home to different ecosystems—communities of different species that depend on interacting with each other and their physical environment for survival. All ecosystems include living things; oxygen and carbon dioxide from the atmosphere; water; and energy from the sun.

Scientists who study living things in their environment are called ecologists. Ecology is the study of living things in their natural environment. The word ecology was coined by German biologist Ernst Haeckel (1834-1919). It is derived from the Greek word “oikos,” which means house. Haeckel saw ecology as the study of the household of living things.

Ecologists want to better understand the interdependence of the living and nonliving parts of an ecosystem. Ecological studies begin when an ecologist notices a pattern in nature.

There are three ways the living parts and nonliving (also called abiotic) parts of an ecosystem interact:

Living-living interactions include food web relationships such as predator/prey relationships and competition.

Living-nonliving interactions include the effects of temperature, light, pressure, salinity, moisture, pH, and nutrient changes on living things.

Nonliving-nonliving interactions include chemical reactions, weathering, and erosion.

In recent years, some ecologists and other scientists have expressed concern that climate change will negatively affect the ability of the blue mussel to attach firmly to rocks. A group of scientists announced in 2013 that the byssal threads become 60 percent weaker when water temperatures are 7 degrees Celsius (15 Fahrenheit) warmer than typical summer temperatures.

New Discoveries

If a population of blue mussels suddenly decreased, the predators would have to compete for fewer food sources. Competition happens in ecosystems whenever two or more organisms require the same limited resource. Organisms on the rocky shores primarily compete for food and space, which is extremely limited because of the unique adaptations required to survive in a rocky shore ecosystem. When any resource becomes more scarce, it has ripple effects throughout the ecosystem. For example, if one food source decreases, the competition among predators often increases because less food is available.

Not all interactions among organisms are driven by the search for food. Remember that a driving force behind all life is the urge to reproduce and pass along genes to future offspring. We can see an example of this in one species of fish. Scientists have long believed that mussels and a tiny fish called the European bitterling had a mutually beneficial relationship, where both species got a survival advantage by working with the other. Scientists thought that female bitterlings laid their eggs inside the mussel, where they were protected until the eggs hatched and swam away. In return, scientists thought the larvae of the mussels could attach to the fish and be carried to new locations, where they could grow and develop.

This relationship between mussels and bitterlings has been used in many textbooks and encyclopedias as an example of a mutually beneficial relationship between two organisms.

However, a scientist named Dr. Carl Smith wanted to learn more about how the bitterlings reproduce. He began to study female bitterlings as they laid their eggs, and he made a surprising discovery. He saw that many female bitterlings lay their eggs in the same mussel, so that some mussels would end up with hundreds of the bitterlings’ eggs. Far from being beneficial to the mussel, Dr. Smith observed that the mussels often stopped growing because they were so overloaded with eggs. Furthermore, studies show that the bitterling doesn’t even carry the mussel larvae to new locations.

A Balanced Ecosystem

These findings tell scientists that the mussel-bitterling relationship is not mutually beneficial at all, and is instead parasitic. Parasitic relationships occur when one organism, the parasite, is dependent on another living organism, the parasite’s host. The parasite survives by taking the host’s nutrients.

As these different interactions show, living things depend on other living things for survival. As organisms interact with one another to carry out their life functions, they act as checks on one another, balancing out population size so no one population grows so much that it drives out other living things.

Ecosystems always seek equilibrium. In order to maintain the balance between all of the organisms and nonliving parts that make up an ecosystem, the interacting parts act as checks on one another. If there are too many organisms competing for the same resources, there will not be enough resources, and some organisms will not survive.

We can understand this by looking at interactions between sea stars and mussels. Experiments have shown that when sea star predators are removed from an ecosystem, the population of mussels explodes. Mussels move farther down in the intertidal zone, smothering the native seaweed. The intertidal zone is the region of land that is covered and uncovered by water between high and low tides. Therefore, the presence of sea stars acts as a natural check on the population growth of the mussels.

For this reason, sea stars are called a keystone species because they have such an important role in maintaining a healthy ecosystem. Without keystone species, the ecosystem would be dramatically different.