Aquatic Ecosystems

1The sea, once it casts its spell, holds one in its net of wonder forever. - Jacques Ives Cousteau

● Aquatic ecosystems, like those on land, have a series of abiotic factors that influence what organisms can survive there.

● Salinity is the amount of dissolved salt in the water.● Salt is formed when rainwater

dissolves rocks, releasing minerals into the water.

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Aquatic Ecosystems

● Water temperature, which is mostly influenced by sunlight.

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● Availability of sunlight, which decreases with water depth.

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Bering Sea, 1300 ft below the surface.Oceandoctor.org

● Oxygen gas, which is dissolved in areas of turbulent water (waves and rapids).

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Whirlpool Rapids Gorge, Niagara River, NY

● Plant nutrients such as nitrates and phosphates, which runoff from land.

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Algae Blooms, Western Lake Erie

● Turbidity, or the cloudiness of the water, is caused by soil eroded from land.

7Confluence of Mississippi River(flows from right) and Minnesota River(flows from top)

● Plankton are free-floating or weakly swimming.● Phytoplankton are plant-like and include

algae.● Zooplankton are animal-like, including

organisms like single-celled protozoa or jellyfish.

● Nekton are strong swimmers and consumers.

● Fish, whales, sea turtles, etc.

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Types of Aquatic Organisms

● Benthos are bottom-dwellers that either anchor themselves to bottom structures or walk along the sea floor.● Sea stars, lobsters, mussels,

etc.

● Decomposers break down dead organisms and wastes into nutrients that can be re-used.● Bacteria.

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● Lakes and ponds contain standing water, some of which is too deep for emergent vegetation.● Emergent vegetation

includes plants that are rooted to the bottom and emerge above the water’s surface.

● Lakes are larger than ponds, but there is no strict defined boundary.

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Lakes and Ponds

● The littoral zone is near the shore and contains shallow, sunlit waters.● Emergent plants are found in this zone.

● The limnetic zone is a photic open water area where rooted plants cannot survive.● Floating phytoplankton

are the only photosynthetic organisms found here.

● This zone extends onlyas deep as sunlightcan penetrate.

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● The profundal zone, directly below the limnetic zone, is aphotic, meaning is receives no sunlight.

● The benthic zone is the bottom of the lake or pond.● Profundal and benthic zones

have no producers.● Food webs are based around

decomposers that feed fromdetritus (dead matter andwaste) that falls down fromabove.

● Oxygen levels are low, limiting the size of anynekton.

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● Ecologists will classify lakes based on their nutrient levels and biological productivity.

● Oligotrophic lakes are very low in nutrients, limiting plankton populations and leaving the water very clear.

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McDonald LakeGlacier National ParkMontana, United States

● Eutrophic lakes have much greater concentrations of nutrients, resulting in heavy growth of phytoplankton.

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Chesapeake BayMaryland, United States

● Streams are narrow channels that carry small amounts of water.

● Rivers are wider and carry more water.● Form when streams combine

with runoff water from the surrounding land.

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Rivers and Streams

Angel Falls, Bolivia

● Rivers are divided into zones, each with different characteristics.

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● The source is the original point from which a river flows – a spring, lake, glacier, or wetland.

● Characteristics of sources include:● High oxygen content● Low nutrient levels● Cold water temperature

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Source of the River Lison, Nans-sous-Sainte-Anne, France

● As the water moves through the transition zone, the streams widen, become deeper, and are warmed by the sun.● Oxygen levels decrease, temperature increases, and nutrient levels rise.

● Low-lying areas, called the floodplains, will occasionally flood and deposit material from upstream.

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● The river eventually ends at a larger body of water. This is called the river mouth. ● Freshwater mixes with saltwater, forming brackish water.

19Moore River meets the Pacific Ocean, Australia

● Freshwater wetlands have water that is regularly at or near the soil surface.

● Marshes are areas of low-lying wetland that do not support the growth of trees.

● Swamps are wetlands that do support trees and dense shrubs.

● Bogs have a floating mass of plant matter and a covering of sphagnum moss.

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Freshwater Inland Wetlands

Volo BogIllinois, United States

● The mosses found in bogs secrete an acid that lowers the pH of the water, slowing down decomposition significantly.● Scientists have discovered

“bog bodies,” remains of people preserved by the acids and other compounds released by the mosses in bogs.

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Tollund Man, a body discovered in 1950 of a man who died between 4-300 B.C.E.

● Marine ecosystems are in or near the oceans, and contain salty water.

● Sunlight and nutrients are the two factors that most limit life in marine ecosystems.● The coasts tend to have the most biologically diverse ecosystems, with

the open ocean having the least.

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Marine Ecosystems

● At the mouth of some rivers, sediment carried by the river will be deposited and form a landmass called a delta.

● Estuaries are bodies of water partially-enclosed within deltas where seawater mixes with freshwater.

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Coastal Wetlands

● A salt marsh is a coastal wetland regularly flooded by tides, and dominated by herbs, grasses, and shrubs.

24Low salt marsh, Great Bay, New HampshirePhoto from New Hampshire Division of Forests and Lands.

● Sea grass beds are wetlands with submerged plants that have long, narrow leaves that resemble grasslands.

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Sea grass bed, Bermuda.Photo from Government of Bermuda Ministry of Environment and Planning.

● Mangrove swamps have trees with complex root systems that can filter salt and withstand flooding and wave action.

26Mangrove swamp, Florida Everglades.

● Wetlands are biodiverse, meaning they support a wide variety of species of animals, plants, fungi, and protists.

● Wetlands protect against flooding by absorbing and retaining excess water.

● Wetlands trap pollutants, resulting in cleaner water that flows out of them.

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Ecosystem Services of Wetlands

● In the coastal zone, life is plentiful due to an abundance of sunlight and nutrients.● About 90% of the

ocean’s biodiversity is found in this zone.

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Marine Aquatic Zones

● Rocky shores are found on coasts with heavy wave activity.

● Sandy shores are found in areas with gentler wave action or that are sheltered.● Black sand is made from

eroded volcanic rock.● Brown sand is made from

eroded granite.● White sand is made from

eroded coral.

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Mindanao Island, Philippines

● The intertidal zone is submerged during high tide and exposed during low tide.● The tides are caused by the gravitational pull of the moon and sun.

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● Tidal range is the vertical difference between high and low tide.● The Bay of Fundy in

Canada has the greatest tidal range at 16.3 meters – taller than a 3-story building.

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● Shallow seas are areas within the coastal zone between the continental shelf and the intertidal zone.● Reach a maximum depth

of about 200 meters.● Receive enough sunlight

to support photosynthetic plankton and algae.

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Shallow Seas

● Coral reefs are shallow sea ecosystems made from the skeletons of small animals called coral polyps that live in the warm coastal waters of the tropics and subtropics.

● Coral polyps are a form a plankton that have a mutualistic relationship with algae.● The coral provides a home, the

algae produce 90% of the polyp’s food through photosynthesis.

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Coral Reefs

● The open ocean is the sunlit top layer of the ocean beyond the continental shelves.● Largest part of the ocean.

● Moving away from the coast, the availability of nutrients decreases rapidly, greatly limiting the growth of photosynthetic plankton.● The open ocean is sometimes

referred to as a “marine desert” due to the relative lack of life.

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Open Ocean

● The characteristics of the water in the open ocean change as you move downwards.● The photic (sunlight) zone contains sufficient sunlight for

photosynthesis.● The dysphotic (twilight) zone sunlight, but not enough for

photosynthesis.● The aphotic (midnight) zone is in complete darkness.

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● Many species living in the aphotic and dysphotic zones are bioluminescent, meaning they can produce and emit light.● Light is produced through chemical reactions or by symbiotic bacteria.● The light can help to find prey or attract mates.

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● The abyssal plain is the sea floor.● Food webs in

the abyssal plain are based on scavenging and decomposition instead of photosynthesis.

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● Marine snow is a shower of organic material that falls from the open water into the abyssal plain.● Decomposers and

scavengers consume this material.

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● Hydrothermal vents are fissures in the ocean floor where heated water and minerals are released into the water.● Certain organisms can use

these compounds as a source of energy, in a process called chemosynthesis.

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