In the previous presentation of the Biomes Journey, we focused on terrestrial biomes. In this fourth presentation, we turn our attention to the other of the two major classes of biomes on Earth – aquatic biomes.

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Previously students investigated the components of biomes and examples of terrestrial biomes. In this section of this Biomes Journey, students will extend their investigation to those biomes within water-aquatic biomes. 

Aquatic biomes, like terrestrial biomes, have living and non-living components. The same factors which affect terrestrial biomes – temperature and precipitation – also affect aquatic biomes. However, understanding and dissociating that climate in an aquatic biome is, in one sense, more complex than that of terrestrial biomes.

When thinking about the climate of an aquatic biome, scientists break down several climatic factors, including the temperature of the water, the depth of water, nutrients in the water, the amount of salt in the water (salinity), and water movement.

Obviously, temperature is a major factor as it is in terrestrial biomes. However, the amount of precipitation tends to exert less influence in aquatic biomes. Precipitation can affect water movement, salinity, and nutrients in the water. But these may also be affected by other factors. 

Scientists have determined that the depth of water, nutrients in the water, water salinity, and water movement have more of a DIRECT effect on plants and animals. Thus, the climate in an aquatic biome is described by describing the five factors listed on this slide and below rather than by only temperature and precipitation, as with terrestrial biomes.

• The temperature of the water
• The depth of water
• Nutrients in the water
• The amount of salt in the water (salinity)
• Water movement

Although students may see different factors that influence terrestrial and aquatic biomes, the point should be made that in BOTH cases, biomes are described and classified in terms of climate. Also, in both cases, plants and animals in different aquatic biomes experience different climates and, therefore, will have different adaptations depending upon the climate.

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As with terrestrial biomes, students may see different groupings of aquatic biomes through different resources.  However, one of the easiest ways to classify aquatic biomes is to divide them into two groups based on salinity: saltwater (marine) and freshwater.

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Over 97 percent of the earth’s water is found in the oceans as salt water. Two percent of the earth’s water is stored as fresh water in glaciers, ice caps, and snowy mountain ranges. That leaves only one percent of the Earth’s water available for our daily water supply needs (U.S. Environmental Protection Agency).

Look at these three views of Earth. All of the blue, except several large freshwater lakes, is saltwater. Focus on the perspective of the largest globe in the center. We can see New Zealand to the lower left and, on the upper right, a small portion of Central and North America. Finally, at the bottom of the globe are the visible ice sheets of Antarctica. This large mass consists of frozen fresh water. All the rest of the globe from this vantage point consists of saltwater marine biomes.

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This slide and the following seven slides are presented to help students explore three types of marine biomes: the open ocean, coral reefs, and estuaries. 

Remind students that in each of these biomes, the water is considered saltwater. 

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The open ocean is filled with a variety of plant and animal life.  One feature of this biome is that it can be further divided into different zones that are unique in the plant and animal life that inhabit it.  The division into zones can occur according to depth alone, the depth at which light penetrates the water, as well as pressure differences. 

The following slides highlight each zone of the ocean, whether plants permeate that zone, and the types of adaptations animals within the zone have.

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The sunlight zone is the top layer of the open ocean. This includes the area next to the shore and farther into the open ocean. Within this entire zone is a great abundance of fish, other marine organisms, plants, and other photosynthetic organisms. It is in this area that plants with stems are found.

Examples of aquatic animals with countershading include sharks, rays and skates, and penguins.  

However, as you move out farther within the open ocean, the depth below the sunlit zone increases to such an extent that plants cannot extend their roots to the ocean floor. Thus, at these larger distances from the shore, the producers in the sunlit zone do not consist of what are technically classified as plants. 

Instead, the producers are phytoplankton. These are microscopic organisms that can photosynthesize, like plants.   These microorganisms provide much of the food for the fish that inhabit the sunlight zone in this region of the ocean. 

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The twilight zone is where bioluminescence (glowing in the dark) first appears because of the low light levels.  Examples of animals in this zone include lanternfish, hatchet fish, anglerfish, and viperfish.

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Lower reaches of the twilight zone are already very dark, with little or no photosynthesis. The midnight zone, as the name implies, has no light. The creatures that call this biome home and those found even deeper are among the strangest on Earth.

As well as perpetual darkness, the midnight zone has very high pressure from all the meters of salt water above it. It is also very cold.

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The pitch-black zone, also called the Abyss, is one of the least understood and hard to get to places on planet Earth. Deep sea trenches, like the Mariana Trench, can be up to 10,984 meters (nearly 7 miles) deep!

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Many scientists consider coral reefs and estuaries as separate biomes due to the unique climate and plant and animal life found in each. 

For example, although coral reefs are part of the ocean, their warm temperatures and shallow depth result in a climate that is different from water of the same depth but of different temperatures and from water with the same temperature but different depths.

Coral reefs are commonly found as barriers along continents and islands. One of the best know reefs is the Great Barrier Reef off the coast of Australia. Unique to coral reefs are coral, organisms that are composed of both algae and animal tissue. The result of this unique combination is that coral can “feed itself.” The algae portion of coral serves as a producer since it can photosynthesize. Additional nutrient needs are met as the animal portion of coral extends its tentacles to obtain plankton from the water. In addition to coral, other fish, sea urchins, octopuses, and sea stars inhabit coral reefs. 

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Estuaries are unique in that they represent a geographical boundary between freshwater and saltwater. 

Estuaries are areas where freshwater from rivers meets the saltwater of oceans. This mixing of freshwater and saltwater creates an aquatic environment with variations in salt content at different areas depending upon the distance from the ocean and during different times of the day due to high and low tides. 

The result of this constantly fluctuating salinity is a biome inhabited by plants and animals with unique adaptations for dealing with this constant change. Plants and animals characteristically found in estuaries include seaweeds, marsh grasses, worms, oysters, crabs, and waterfowl.

Estuaries often have areas of salt marsh between which the water flows and mixes. A salt marsh is a form of wetland common along protected shorelines. The salt marshes are the “nurseries” of the estuary, where many newly hatched fish, crabs, and shrimp are protected from predators until they grow large enough to fend for themselves in the open waters of the estuary, where they remain until they are grown and large enough to move into the open ocean.

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In addition to marine or saltwater biomes, the Earth is home to three major types of freshwater biomes: lakes and ponds, rivers and streams, and wetlands.

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Students will likely be very familiar with the freshwater biome of lakes and ponds. Although not completely delineated here, lakes and ponds can be divided into zones similar to the open ocean biome. These zone boundaries are defined by the distance from the shore and the depth of water. Each zone differs in its plant and animal life due to differences in light penetration, lake or pond floor depth, and temperature.

The area close to the shore can be established as one zone. Most plants are found in this area because their roots can easily find the lake or pond bed. As a result of the rich plant life, there is a myriad of invertebrates, crustaceans, and amphibians in this zone. 

Farther out in the lake, the top layer of water is similar to the area close to the shore in its ability to support life and nutrients. Although plants are generally not found here because the lake or pond bed is at a much greater depth, photosynthesis is prevalent and carried out by microscopic organisms known as phytoplankton.  Fish such as bass and trout feed off this plankton and other types of plankton. The water in this top layer and the water close to shore tend to be much warmer than a lake’s deeper waters.

The deeper waters of a lake or pond are considered a third zone within the lake or pond. In this area, the depth is such that light does not penetrate well, so photosynthesis does not occur at significant rates. The lack of light and the lack of plants and photosynthesizing plankton result in this zone being dark, cold, and low in oxygen. Animals in this zone are adapted to these conditions. Their nutrient source comes mainly from the dead and decaying matter that falls from the zones above. 

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Rivers and streams represent a second type of freshwater biome. They differ from lakes and ponds in several ways. One of the most obvious is that the water in these biomes is moving. As a result, the water in rivers and streams tends to be colder than in lakes and ponds. Thus, temperature differences exist between these two types of biomes.

As with other aquatic biomes, rivers and streams can be divided into different areas. For rivers and streams, three different zones are generally described: the head or beginning of the river, the middle, and the end of the river. These three areas exhibit temperature, oxygen content, turbidity, and sediment accumulation differences. As you might expect, these factors often combine to produce a difference in water conditions that results in a difference in the plants and animals that inhabit that area.

For example, the headwaters of a river or stream tend to be cooler and have more oxygen than the water at the mouth of the stream. Salmon, similar to the trout shown in this slide, are found in these cooler, more oxygen-rich areas of rivers, whereas carp and catfish are found in warmer mouth sections as these are species that require less oxygen. 

The middle of the river tends to be an area of great species diversity as the width of the river increases.  The head and middle of the river tend to have more plant diversity than the mouth of the river because of differences in the amount of light penetrating these areas. Towards the mouth of the river, the water becomes more turbid or murky compared to the head or middle of the river because of the sediment picked up by the water along its course. As a result of this increase in sediment, less light can penetrate the water, leading to lower levels of photosynthesis and less plant diversity.

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The last freshwater biome discussed in this section is the wetlands biome. Students should be familiar with this biome and some of the adaptations of its plants as a result of completing the Exploring Ecosystems CELL.

Wetlands are one of the most intriguing biomes because of the unique adaptations of their plants. In addition to the examples listed on the slide, hydrophytes have evolved structures and functions that allow them to function in this biome. Although students may assume that these adaptations are all directed at living with large amounts of water, hydrophytes and other plants of the wetlands must also deal with variations in water levels as some wetlands do not remain moist or filled with water during all portions of the year. 

One of the ecological functions of wetlands is that it serves as a sponge or reservoir for water from nearby rivers and streams. For some wetlands, there is a portion of the year when the wetlands have what would be considered an excess of water. However, water from some of these wetlands recedes during drier portions of the year or droughts. Thus the plants that thrive in the excess water conditions must also be able to tolerate lower levels of water. 

Wetlands also filter the chemicals and sediments that pass from the land to the ocean. This is because as water runs off the land and passes through a wetland, many sediments become trapped by the vegetation and settle into the soil and sediments. Many of the chemicals carried along with the water and sediments are often converted into less toxic forms by the plants of the wetlands.

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Answer:

Question 1: A

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Answers:

Question 2: A

Question 3: C