Aquatic Biomes
Objective: Explain the characteristics of the aquatic biome
Aquatic systems are of two types: freshwater and marine. Physical factors important to both include depth of sunlight penetration, water temperature, and the concentration of dissolved nutrients. There are linkages between aquatic systems and terrestrial biomes, such as forest litter enriching a stream or salmon returning from the sea to spawn. In tropical rain forests, floods give fish access to seeds of tropical trees which they help disperse. Seabirds breeding in coastal areas transport nitrogen and phosphorus from marine systems back to land by producing guano.
Learn more: http://www.worldbiomes.com/biomes_aquatic.htm
The Freshwater Biome
Freshwater is defined as having a low salt concentration – usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean).
Learn more: http://www.ucmp.berkeley.edu/exhibits/biomes/freshwater.php
There are different types of freshwater regions:
Ponds and lakes
These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciation. Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different “zones” which are usually determined by depth and distance from the shoreline.
Learn more: http://www.mbgnet.net/fresh/lakes/index.htm
The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sun’s heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this zone. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks.
The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well-lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Plankton are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone.
Plankton have short life spans when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration.
Temperature varies in ponds and lakes seasonally. During the summer, the temperature can range from 4 0 C near the bottom to 22 0 C at the top. During the winter, the temperature at the bottom can be 4 0 C while the top is 0 0 C (ice). In between the two layers, there is a narrow zone called the thermocline where the temperature of the water changes rapidly. During the spring and fall seasons, there is a mixing of the top and bottom layers, usually due to winds, which results in a uniform water temperature of around 4 0 C. This mixing also circulates oxygen throughout the lake. Of course there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.
Streams and rivers
These are bodies of flowing water moving in one direction. Streams and rivers can be found everywhere they get their starts at headwaters, which may be springs, snowmelt or even lakes, and then travel all the way to their mouths, usually another water channel or the ocean. The characteristics of a river or stream change during the journey from the source to the mouth. The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found there. Towards the middle part of the stream/river, the width increases, as does species diversity, numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that require less oxygen, such as catfish and carp, can be found.
Learn more: http://www.thewildclassroom.com/biomes/stream.html
Wetlands
Wetlands are areas of standing water that support aquatic plants. Marshes, swamps, and bogs are all considered wetlands. Plant species adapted to the very moist and humid conditions are called hydrophytes. These include pond lilies, cattails, sedges, tamarack, and black spruce. Marsh flora also includes such species as cypress and gum. Wetlands have the highest species diversity of all ecosystems. Many species of amphibians, reptiles, birds (such as ducks and waders), and furbearers can be found in the wetlands. Wetlands are not considered freshwater ecosystems as there are some, such as salt marshes, that have high salt concentrations these support different species of animals, such as shrimp, shellfish, and various grasses.
Learn more: http://water.epa.gov/type/wetlands/index.cfm
Marine ecosystems cover 70% of the earth’s surface. The majority of life in the open ocean is in the euphotic zone, which extends from the surface to the limit of sunlight penetration. The base of the food chain is microscopic, photosynthetic phytoplankton. However, the productivity of this zone is low, comparable to a desert. This is because there are limited nutrients. Organic material from dead organisms sinks to the bottom and nutrients are not recycled up to the surface except in some areas where there are upwellings due to currents. Animal communities at the bottom of the ocean are either supported by this continuous rain of nutrients, or associated with hydrothermal vents.
The most productive regions in the ocean are in coastal areas and coral reefs. Coastal areas, such as estuaries, are productive because they receive a steady input of nutrients from the rivers that run into them. Coral reefs have productivity levels and species comparable to that of a tropical rain forest. This is because the shallow, clear, warm waters allow much photosynthetic activity, which in turn supports a large animal biomass. Environmental scientists have documented moderate to severe declines in coral reef health during the 1990s, and increased attention is being given to monitoring programs and conservation plans that reduce human impacts.
Freshwater ecosystems include ponds and lakes (standing water) and streams and rivers (flowing water). In ponds and lakes, as in the ocean, there is a vertical stratification due to vertical changes in light penetration, nutrient levels, temperature, and dissolved oxygen. The littoral zone is shallow enough to have rooted vegetation. The limnetic zone is the open water and phytoplankton are the base of the food chain. Animals tend to be stream-lined and good swimmers. Bottom dwellers are found in the benthic zone (profundal zone in the deepest water), and tend to attach themselves to substrate or burrow.
Wetlands are ecosystems that have standing water at least part of the year and have vegetation adapted to growing while plant roots are covered with water. Included in the broad wetland category are swamps, marshes, bogs, and fens. Swamps and marshes have very high productivity, because they receive nutrients through runoff from adjacent land. Bogs and fens have low productivity because they are closed systems. Wetlands are major breeding areas for waterfowl. Wetlands also perform services useful to humans, purifying water and reducing flooding. Despite their biological diversity and usefulness, the U.S. has lost over half of its wetlands to human development in less than 200 years.
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Review Questions
1. Identify the two types of aquatic biomes. Locate one of each of these types of biomes nearest you.
2. Describe the structure and composition of a freshwater biomes.
3. Describe the structure or composition of a marine biome.
4. Explain the composition of wetlands and identify why wetlands are so crucial to the environment.
5. What is the biggest threat to the aquatic biomes today? Explain
