Aquatic EcosystemsHow do we describe aquatic ecosystems?

Aquatic ecosystems are primarily determined by the ecosystem’s salinity. Salinity refers to the dissolved salt content of the water.

Aquatic ecosystems are divided into freshwater and marine ecosystems.◦ Freshwater ecosystems have a very low salt

content.◦ Marine ecosystems have a very high salt content.

Note that organisms adapted to one type of aquatic ecosystem often cannot survive in the other ecosystem type.

Aquatic Ecosystems

Several factors determine the organisms that dwell within the water.◦ Temperature◦ Sunlight◦ Oxygen◦ Nutrients◦ Soils and minerals

Example: sunlight only penetrates water to a certain depth, so photosynthetic organisms are restricted to a certain water depth.

Freshwater Ecosystems

Plankton are organisms that cannot swim against currents.◦As such, they are

called drifters. Phytoplankton are

drifting algae, and serve as the food base for the ecosystem.

Freshwater Ecosystems

Zooplankton are drifting animals. They may be microscopic, but do not have to be.◦ Jellyfish are a good

example. Decomposers are also

found in aquatic ecosystems.

Freshwater Ecosystems

Nekton are free-swimming animals.◦These organisms

can freely oppose the water’s current.

Benthos are “bottom-dwellers”, which means they inhabit the floor or anchor to hard surfaces.

Freshwater Ecosystems

Lakes and ponds are separated into three zones:◦ The littoral zone, located around the shore.

Here, life is both diverse and abundant. Cattails, reeds and lilies are common plants in this zone.

◦ The limnetic zone is found in the shallow open water farther away from the shore. Since the water is often too deep to support rooted plants, phytoplankton is the primary food base.

◦ The benthic zone is the very bottom of the lake or pond. It’s mostly inhabited by bottom dwellers and decomposers.

Lakes and Ponds

Eutrophication is any increase in the amount of nutrients in the ecosystem.

As you know, this is not really a good thing for the ecosystem. The excessive influx of nutrients causes algal blooms, which choke out local organisms.

Additionally, the growth of algae and other producers brings with it an expansion in the number of bacteria and other decomposers. This uses up most of the dissolved oxygen.

Lakes and Ponds

Wetlands are terrestrial regions that are covered with fresh water for a large part of the year.◦ Marshes are

populated by non-woody plants (i.e., cattails).

◦ Swamps are populated by woody plant (i.e., cypress and other trees).

Wetlands perform several important roles in nature:1. They filter pollutants

from the water.2. They control flooding

by absorbing excess overflow.

3. Fish use these lands for food and breeding.

4. Carbon dioxide can be trapped here.

Freshwater Wetlands

Humans have drained and developed a large number of wetlands.◦ For example, the Everglades have been reduced

from 8 million acres to 2 million acres today. The resulting loss of wetland habitats has

led to increased pressure on wildlife populations.

Also, the loss of wetlands has made several areas of the world more vulnerable to flooding, which can cause damage to life and property.

Human Effects

Rivers can form from springs, melting snow, or converging streams.

At the headwaters, the river is typically cold, oxygenated, and narrow and quick.

Further downstream, the river becomes warmer, wider, slower, and deoxygenated. Vegetation is more frequent here.◦ Vegetation and animals adapt to the different

parts of the river. For example, trout are good swimmers, and are found in the rapids. Catfish are frequently found in the slower waters.

River Systems

1. Why are phytoplankton not found in deep water?

2. Which of the three zones of a lake has the greatest variety of vegetation?

3. How can eutrophication damage ecosystems?

4. What are some negative consequences of removing wetlands?

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Marine ecosystems contain salt water. There are three different types:◦ Coastal Wetlands◦ Coral Reefs◦ Open Ocean

All three of these marine ecosystems have their own unique characteristics.

Marine Ecosystems

Much like freshwater wetlands, coastal wetlands are terrestrial areas that are flooded some or all of the time. The only difference is that salt water is used instead of freshwater.

Just like freshwater wetlands, coastal wetlands guard against flooding, filter pollutants and minerals, and provide food and shelter to wildlife.

Coastal Wetlands

Estuaries are regions where fresh and salt water mix. Often, this occurs when a river meets the ocean.

When this occurs, mixing currents from the river and ocean trap mud and nutrients, sinking them to the bottom.

As a result, estuaries are often quite lush and productive. Producers can make great use of these nutrients.

Coastal Wetlands

Due to the high level of nutrients and sunlight, estuaries can support a wide variety of living organisms.◦ Drifters: Phytoplankton, zooplankton◦ Nekton: Dolphins, manatees, otters, fish◦ Benthos: Oysters, barnacles and clams

Organisms that live in estuaries often must be able to tolerate a wide range of saline levels, due to the variable salt content of the estuary’s water.

Coastal Wetlands

Much like freshwater wetlands, estuaries have been developed for human use.

Landfills are a common human use for estuary development.

Estuaries are also used as harbors or port areas.◦ Tokyo◦ New York◦ Shanghai◦ Buenos Aires◦ Rio de Janeiro◦ Bombay

Coastal Wetlands

Salt marshes are filled with mineral-rich mud, deposited due to the mixing currents within an estuary.

Mangrove swamps are comprised of mangroves, which are well adapted to shallow salt water. They are found in swampy regions in the tropics and subtropics.

Barrier islands are formed from sand deposits away from the shore. They function as vital breakwaters, protecting the mainland from flooding.

Coastal Wetlands

Coral reefs are limestone ridges. They are formed by coral polyps and algae. The polyps secrete limestone frames and skeletons, which accumulate over time to form the reef.

These corals can only exist in warm salt water with abundant light (for photosynthesis). Many are found in the Pacific and Indian Oceans, as well as the Caribbean.

Corals shelter fish, snails, anemones, sponges, and many other organisms.

Coral Reefs

Coral reefs are quite sensitive to environmental flux. Either sudden or gradual changes in the water temperature, mineral and nutrient content, and overall health will kill off the algae found in the coral reef.

This leads to coral bleaching – the sudden whitening of the corals. If the algae is not replaced, then the ecosystem will die.

Also, pollutants like waste and oil slicks cause damage to these ecosystems. Note that coral reefs grow slowly, so ecological damage is repaired slowly, if at all.

Coral Reefs

As open ocean is quite harsh, this is one of the least productive biomes of all.

Water scatters light, and sunlight for photosynthesis only penetrates about 100m. Phytoplankton is restricted to this depth.

The vast majority of ocean lifeforms exist in shallow coastal water. This is due to the scattering of light, and because shallow water is close enough to land to support plant life.

Oceans

The deep ocean and ocean floor are very dark. Most food here is dead organisms that fall from the surface waters. Decomposers, filter feeders and other predators are the primary lifeforms here.

Chemosynthetic organisms also live here. These are organisms that make their own food from chemical reactions.

Oceans

Oceans face several man-made threats:◦ Added pollution from land can kill off organisms in

the ocean. Pollutants include runoff, waste, fertilizers and sewage.

◦ Overfishing damages the food web by removing vital links in the ecosystem.

◦ Overwarming and acidification of the ocean can also eliminate organisms that can’t adapt to changing environmental conditions.

Oceans

1. Why are estuaries so diverse and productive?

2. What are some negative side effects of the removal of estuaries?

3. Why are coral reefs so easily harmed and damaged?

4. The deep ocean has little, if any, light. Without light for producers, how can any organisms exist in this region?

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