Module #13

Aquatic Biomes

Module Introduction:

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• Whereas terrestrial biomes are categorized by dominant plant growth forms, aquatic biomes are categorized by physical conditions such as salinity, depth and water flow.
• Temperature is an important factor in determining which species can survive in a particular aquatic habitat, but it is not a factor used to categorize aquatic biomes.
• Aquatic biomes fall into two broad categories: freshwater and marine.
• Freshwater biomes include streams, rivers, lakes and wetlands.
• Saltwater biomes, also known as marine biomes, include shallow marine areas such as estuaries and coral reefs as well as the open ocean.

Module #13: Aquatic Biomes

Essential Knowledge

1.3 Aquatic Biomes (Module 13)

• Freshwater biomes include streams, rivers, ponds, and lakes. These freshwater biomes are a vital resource for drinking water.
• Marine biomes include oceans, coral reefs, marshland, and estuaries. Algae in marine biomes supply a large portion of the Earth’s oxygen, and also take in carbon dioxide from the atmosphere.
• The global distribution of nonmineral marine natural resources, such as different types of fish, varies because of some combination of salinity, depth, turbidity, nutrient availability, and temperature.

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Essential Knowledge

8.4 Human Impacts on Wetlands and Mangroves (Modules 13, 60)

• Wetlands are areas where water covers the soil, either part or all of the time.
• Wetlands provide a variety of ecological services, including water purification, flood protection, water filtration, and habitat.
• Threats to wetlands and mangroves include commercial development, dam construction, overfishing, and pollutants from agriculture and industrial waste.

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Essential Knowledge

9.10 Human Impacts on Biodiversity (Modules 1, 12, 13, 59-61)

• HIPPCO (habitat destruction, invasive species, population growth, pollution, climate change, and over exploitation) describes the main factors leading to a decrease in biodiversity.
• Habitat fragmentation occurs when large habitats are broken into smaller, isolated areas. Causes of habitat fragmentation include the construction of roads and pipelines, clearing for agriculture or development, and logging.
• The scale of habitat fragmentation that has an adverse effect on the inhabitants of a given ecosystem will vary from species to species within that ecosystem.
• Global climate change can cause habitat loss via changes in temperature, precipitation, and sea level rise.
• Some organisms have been somewhat or completely domesticated and are now managed for economic returns, such as honeybee colonies and domestic livestock. This domestication can have a negative impact on the biodiversity of that organism.
• Some ways humans can mitigate the impact of loss of biodiversity include creating protected areas, use of habitat corridors, promoting sustainable land use practices, and restoring lost habitats.

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Aquatic Biomes

• Aquatic biomes are defined by their salinity, depth and water movement.
• There are 2 major types: freshwater and marine.

Salinity = salt concentration

Streams and Rivers

• Flowing freshwater that may originate from underground springs or as runoff from rain or melting snow.
• Streams are typically narrow and carry relatively small amounts of water whereas rivers are usually wider and carry larger amounts of water.
• Streams and rivers typically have higher dissolved oxygen than other aquatic biomes due to their colder temperatures and the rapid surface movement that aerates them.

Just like atmospheric

oxygen, dissolved oxygen supports the

growth of organisms.

Stream Assessment

Streams and riparian zones are evaluated visually on a number of factors:

• Odor, turbidity, surface coating and stream flow
• Stream width, depth and velocity
• Canopy cover (%), abundance of woody debris, predominant aquatic vegetation, algae growth/location, litter concentration and human structures (eg. bridges, culverts, etc.).
• Land use characteristics (eg. agriculture, athletic fields, residences, etc.)
• Channel alteration, occurence of riffles (small rapids), streambank stability, vegetative protection and riparian zone width.

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Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.

Riparian: Wetland ecosystems adjacent to rivers and streams.

Except for the concept of turbidity, this is probably beyond this course and the AP Exam, but still interesting and relevant!

Stream and Riparian Health

More complex streams/riparian zones are healthier:

• A mix of snags, submerged logs, undercut banks and stream velocities all help provide habitat for epifauna and fish species → higher biodiversity.
• Stream sediment should be predominant over gravel, rocks and boulders and streambanks should be stable and have an abundance of native plant growth in riparian zones.
• Vegetative growth improves canopy cover, providing climate control, reducing water temperatures and improving dissolved oxygen content for sensitive, native species like trout.
• Wider riparian vegetation zones improve stream health by acting as a buffer to human activities and pollution including road salt.

Epifauna: animals living on the surface of the seabed or a riverbed, or attached to submerged objects or aquatic animals or plants. Also known as Macroinvertebrates.

This is probably beyond this course and the AP Exam, but still interesting and relevant!

Macroinvertebrates and Stream Health

• Macroinvertebrates, particularly aquatic insects, serve as valuable biological indicators of stream health, reflecting the overall condition of the water body.
• Their presence, absence, and diversity provide insights into water quality, habitat conditions, and the presence of pollution.

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This is probably beyond this course and the AP Exam, but still interesting and relevant!

Aquatic macroinvertebrates are small organisms that have no internal skeletal system and live part or all of their lives in water. They are ubiquitous in freshwater ecosystems around the world. They comprise a rich and diverse group of organisms that includes insect larvae, worms, snails, crayfish, and other crustaceans, such as clam shrimp, fairy shrimp, and water fleas.

Conservation Spotlight:

Rainbow Trout

• Rainbow trout are an oxygen loving species and therefore inhabit cold streams and rivers since colder water holds more dissolved gasses than warmer water. They live on a gravelly bottom with enough vegetation that provides shelter.
• Because of their high water quality and habitat requirements, trout are valuable indicators of healthy aquatic ecosystems.

Indicator species are defined as species which can provide information on ecological changes and give early warning signals regarding ecosystem processes in site-specific conditions due to their sensitive reactions to them.

This is probably beyond this course and the AP Exam, but still interesting and relevant!

Lakes and Ponds

• Lakes and ponds contain standing water, at least some of which is too deep to support emergent vegetation.
• Lakes are larger than ponds but there is no clear point at which a pond is considered large enough to be called a lake.
• The dividing line between the two uses surface area, depth and the percentage of emergent vegetation as seen in the illustration to the right.

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Zonation of Lakes and Ponds

• The littoral zone consists of shallow water with emerging, rooted plants whereas the limnetic zone is the deeper water where plants do not emerge.
• The deepest water, where oxygen can be limiting because little sunlight penetrates to allow photosynthesis by producers, is the profundal zone.
• The sediments that lie beneath the littoral, limnetic, and profundal zones constitute the benthic zone.
• Remember: *Littorally Lick Peanut Butter*

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The benthic zone would have a high rate of decomposition due to the build up of organic matter at the bottom of the lake/pond.

Turnover in Ponds and Lakes

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• Due to its chemistry, water is most dense at 4℃.
• As autumn temperatures drop, the upper layers of the pond water grow colder and heavier. The upper water sinks and mixes with the layers below.
• The reverse occurs in spring as the pond/lake thaws.
• Benefit: Turnover redistributes nutrients and promotes new growth.

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Turnover: the gentle, natural mixing of pond and lake waters.

National Geographic: Lake Turnover

Video: How Lakes Cycle

Lake Productivity

Lakes are classified by their level of primary productivity.

• Oligotrophic: Describes a lake with a low level of productivity.
• Mesotrophic: Describes a lake with a moderate level of productivity.
• Eutrophic: Describes a lake with a high level of productivity.

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Break it Down:

• “Oligo” means “few or scanty.”
• “Meso” means “middle”.
• “Eu” means “pleasant, good or true”.
• “Troph” means nourishing/stimulating

This is probably beyond this course and the AP Exam, but still interesting and relevant!

The Triplets

• Freshwater wetlands, saltwater marshes and mangrove swamps are all highly related biomes despite their differences.
• All 3 represent transitional biomes that exist on the edge of terrestrial and aquatic.
• All 3 provide similar and enormously important ecosystem services.

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The triplets, as well as forests in general, also provide protection to coral reef ecosystems. By preventing erosion, fewer sediments can pollute coastal waters, providing the clear conditions needed for corals to grow in.

Coastal wetlands (saltwater marshes and mangrove swamps) make up only 5% of the planet’s surface area but store 25% of all the carbon found in soil (regulating service). This is because of anoxic soil conditions that prevent the decomposition of organic material.

Freshwater Wetlands

• Freshwater wetlands: An aquatic biome that is submerged or saturated by water for at least part of each year, but shallow enough to support emergent vegetation. Includes swamps, marshes and bogs.
• Contain species specialized for living in saturated soils.
• Wetlands represent some of the most productive ecosystems and offer tremendous ecosystem services like flood control.
• Productivity: The rate of generation of biomass in an ecosystem, usually through photosynthesis.

The Clean Water Act protects wetlands through a “No-Net-Loss Policy”: any wetlands that are destroyed by development, must be replaced with new wetland habitat.

Wanna learn more? Check out this episode on wetlands from the Biologic Podcast.

Current Events: Wetlands Protections

• “The U.S. Supreme Court has ruled in Sackett v. EPA that federal protection of wetlands encompasses only those wetlands that directly adjoin rivers, lakes and other bodies of water. This is an extremely narrow interpretation of the Clean Water Act that could expose many wetlands across the U.S. to filling and development.” (2023)

Saltwater Marshes

• Saltwater marsh: A marsh containing nonwoody emergent vegetation, found along the coast in temperate climates.
• Saltwater marshes often form in estuaries where rivers meet the ocean resulting in brackish water.
• Rivers provide lots of nutrients to stimulate growth making saltwater marshes highly productive ecosystems with high degrees of biodiversity.
• Ecosystem Services: saltwater marshes can help reduce coastal flooding, protecting homes and real estate (regulating).
• Brackish water: a mixture of marine and freshwater.

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Estuary: a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.

Wanna learn more? Check out this episode on wetlands from the Biologic Podcast.

Conservation Spotlight:

Diamondback Terrapins

• Diamondback terrapins live in the brackish water of salt marshes, estuaries, and tidal creeks where they feed on fish, marine snails, crabs, marine and tidal mollusks, carrion, clams, and worms.
• This gives terrapins a critical environmental niche as secondary and tertiary consumers in marsh ecosystems.

This is probably beyond this course and the AP Exam, but still interesting and relevant!

Vulnerability to Climate Change

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• As glaciers and ice sheets melt and the oceans warm, sea levels rise.
• Ironically, areas further away from these glaciers and ice sheets (like the East Coast) will experience the bulk of sea level rise.
• This is because the land underneath the ice rebounds, growing taller and deflecting higher sea levels somewhere else.
• This leaves coastal wetlands especially vulnerable to sea level rise.
• Accretion will be unable to balance the impacts of subsidence (sinking of a land surface), erosion and sea level rise.

Accretion: The growth of a marsh by the deposition of suspended particles during flooding and by accumulation of plant material, both roots and decomposed material from plants growing in the marsh.

Mangrove Swamps

• Mangrove swamp: A swamp that occurs along tropical and subtropical coasts, and contains salt tolerant trees with roots submerged in water.
• Mangrove trees are salt tolerant; these trees can actually prevent salt uptake in their roots and excrete excess salt from their leaves.
• Like freshwater wetlands and saltwater marshes, mangrove swamps provide enormously important ecosystem services including:
• Controlling coastal flooding and erosion, which protects coral reefs.
• Providing nursery habitat for aquatic species (eg. fish and shrimp).

Resources:

Importance of Mangroves

Mangrove Model

Mangrove Case Study: Hurricane Matthew

• Hurricane Matthew (2016, category 5) did a surprising amount of damage to Haiti and less to the Dominican Republic despite both nations occupying the same island.
• The reason was deforestation: Haiti had removed the majority of its rainforests and mangroves while the Dominican Republic retained moderate forest cover (Module 6).
• The mangroves helped reduce storm surge and the trees held soil in place, minimizing the impact of flooding and erosion.

Intertidal Zones

• Intertidal zone: The narrow band of coastline between the levels of high tide and low tide.
• Highly variable biome: stable during high tide but harsh when the tide goes out.
• Organisms must tolerate direct sunlight, high temperatures and dehydration during low tide as well as the constant physical assault of ocean waves.

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Intertidal Zone

Coral Reefs

• Coral reef: The most diverse marine biome on Earth, found in warm, shallow waters beyond the shoreline.
• Corals are invertebrate organisms that secrete calcium carbonate to form an exoskeleton.
• Corals form a mutualistic relationship with photosynthetic algae.
• Corals grow in large colonies to form reefs. When individual corals die, their exoskeleton remains providing habitat for other organisms.
• Coral reefs are indirectly threatened by deforestation. Forests capture carbon dioxide, helping to mitigate ocean acidification and the forests also hold soil in place, provide clear water for the coral to grow in.

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CO₂ and Shelter

Glucose

Coral reefs have some of the highest biodiversity on Earth and like Mangrove swamps, provide nursery habitat for many species. Coral reefs also provide opportunities for ecotourism and are popular vacation destinations.

Open Ocean

• Open ocean: Deep ocean water, located away from the shoreline where sunlight can no longer reach the ocean bottom.
• Photic zone: The upper layer of ocean water in the ocean that receives enough sunlight for photosynthesis.
• Aphotic zone: The deeper layer of ocean water that lacks sufficient sunlight for photosynthesis.
• Because of the sheer vastness of the oceans, the productivity of the open oceans (due mostly to phytoplankton) is the highest among all biome types.

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With no available sunlight for photosynthesis, the organisms living in the aphotic zone of the open ocean must rely on other sources of energy and carbon. Chemosynthesis can occur here using hydrogen sulfide from deep sea vents as well as “whale falls”.

Wanna learn more? Check out this episode on oceans from the Biologic Podcast.

Deep Ocean: Chemosynthesis

In the aphotic zone of the world’s oceans, chemosynthesis often replaces photosynthesis as the foundation of ecosystems.

Chemosynthesis: the synthesis of organic compounds by bacteria or other living organisms using energy derived from reactions involving inorganic chemicals, typically in the absence of sunlight.

Chemosynthesis typically occurs near hydrothermal vents which supply hydrogen sulfide gas due to geothermal activity.

Deep Ocean: Whale Falls

• When whales die, they sink to the ocean floor.
• Their organic tissues will serve as an important source of food for organisms that will quickly consume the dead whale.

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The Value of Aquatic Biomes

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Module Review:

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• In this module, we have learned that aquatic biomes are characterized by physical features such as salinity, depth and water flow.
• Freshwater biomes include streams and rivers, which have flowing water, and lakes, ponds and wetlands, which have standing water.
• Marine biomes contain salt water and include salt marshes, mangrove swamps, intertidal zones, coral reefs and the open ocean.
• Differences in water flow, depth and salinity help us understand why different species of producers and consumers, including commercially important species of fish and shellfish, live in different aquatic regions of the world.