Lesson 4: Marine Ecosystems and Estuaries

Getting Started

In today's lesson, you will investigate the distribution of water on the planet and why this is significant. You will begin to understand more about the abundance of places that make up the hydrosphere, the importance of oceans and estuaries, and the significant contribution each one makes to life on Earth.

Stuff You Need

  • eggs prepared in Lesson 2
  • pen
  • saline water
  • scale (kit)
  • slotted spoon
  • small clear cups (kit)
  • tap water
  • tape

Ideas to Think About

  • What are some differences among marine ecosystems and the organism that live within them?
  • How do minerals/nutrients influence an organism in a marine ecosystem?

Things to Know

  • An estuary is a partially open coastal body of water that has at least one river flowing into it.
  • Photosynthesis is a process that converts sunlight and carbon dioxide into organic food by using the energy from sunlight.
  • Chemosynthesis is a process that uses nitrogen or sulfur compounds to make food. Chemosynthesis occurs in regions where the energy from the Sun is not available for photosynthesis.
  • Predation is the act of organisms that do not make their own food hunting other organisms for nutrition.
  • Nekton are organisms that swim freely in marine ecosystems.
  • Plankton are organisms that use the currents as transportation in marine ecosystems.


  • Analyze evidence to explain observations, make inferences and predictions, and develop the relationship between evidence and explanation. (S)
  • Analyze and evaluate information from a scientifically literate viewpoint by reading, hearing, and/or viewing scientific texts, articles, and events in the popular press. (S)
  • Explain the structure of the hydrosphere including water distribution on Earth, local river basin, and local water availability. (S)
  • Evaluate evidence that Earth's oceans are a reservoir of nutrients, minerals, dissolved gases, and life forms such as in estuaries and marine ecosystems. (S)

Introducing the Lesson

In this lesson, your child will be introduced to the variety of marine ecosystems present in the hydrosphere. She will also be reading and learning about the processes and energy relationships in the ocean. Life is dependent on these processes, so it will be important for your child to always remember the dependence of life on the ecosystems in which it is found. As your child reads, she will be asked to think about these ecosystems and the influences upon them. As with the previous lessons, your child will need to consider the importance of water to life and how the living components contained within a marine ecosystem depend upon and interact with the hydrosphere.

Your child will take another step in the scientific process as the activity for this lesson focuses on the influence of a mineral on an organism. In the activity involving the egg, your child will be challenged to hypothesize about what will happen when a mineral is introduced into an aquatic environment. The goal of this unit to develop your child's ability to make draw conclusions based on evidence as well as understand cause and effect relationships.
Reading and Questions
Read about marine ecosystems on the links provided. Then read the "Why Are Estuaries Important?" section on the "Basic Information About Estuaries" web page. As you read, you will learn about life processes in the ocean. Keep in mind the importance of estuaries.
  1. Where are estuaries located? What types of habitats are found there?
    Estuaries are places near shorelines where salt and fresh waters mix. A wide variety of habitats are found in estuaries, including marshes, swamps, open water, and beaches.
  2. Why are estuaries called the nurseries of the ocean? What makes estuaries the best place for new organisms to develop?
    Most marine organisms spend the early part of their lives in estuaries. Because estuaries exist where rivers feed into the ocean, they have both fresh and salt water. The river waters bring a lot of nutrients to the estuaries, ensuring that the organisms at the base of the food chain are plentiful. Estuaries also tend to have fewer predators and more food, so the microscopic offspring of most marine organisms have a greater chance for survival.
  3. Why do you think that estuaries are better as marine nurseries than a coral reef or a rocky shore area/beach?
    Answers will vary but may include the following: fewer predators, an abundance of food sources (nutrients and minerals), and numerous places where the organisms can hide or gather without being eaten/ingested by predators.
  4. Where in the open ocean can photosynthesis occur? Why not in deeper areas?
    Photosynthesis occurs in a narrow band near the surface called the photic zone. In deeper areas, not enough light can penetrate to allow phytoplankton to use photosynthesis.
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