Aquatic Ecology

Environmental Factors for Aquatic Life

• Light penetration• pH (acidity / alkalinity)• Salinity (salt content)• Dissolved Oxygen (DO)• Mineral nutrients• Water depth• Water movement (currents, flow rates)

Life in aquatic ecosystems

• Plankton: free-floating, carried by currents / waves. Ex: Phytoplankton (photosynthetic) and Zooplankton (animal-like).

• Nekton: free-swimming organisms. Ex: fish, turtles.

• Benthos: “bottom dwellers” Live in the benthic zone (sponges, crabs, clams), some may be sessile (meaning they do not move)

Freshwater ecosystems

• Are classified as:

- standing (lakes and ponds)- flowing (rivers and streams/creeks)- wetlands (swamps, marshes, and bogs)

Aquatic zones in lakes and ponds

• Littoral zone – the shallow area of soil and water near the shoreline. Many photosynthetic organisms find habitat in this zone. Ex: algae & rooting plants like cattails.

• Limnetic zone – deeper, open water where no rooting plants can find habitat. The zone extends down as far as light can penetrate. Free-floating organisms find habitat here. Ex: algae (phytoplankton)

Aquatic zones in lakes and ponds

• Profundal zone – deeper water below the limnetic zone. No photosynthetic organisms grow here. Bacteria feed on detritus from the limnetic zone.

• Benthic zone – the muddy bottom of a lake or pond below the profundal zone.

Aquatic zones

Benthic Zone Profundal Zone

Freshwater Wetlands-Characteristics-

• Areas submerged or saturated by water for all or part of a year.

• Shallow enough to support emergent vegetation.

• Vegetation specialized to live in submerged or saturated soils.

• Categories of freshwater wetlands include: swamps and marshes, and bogs.

Freshwater Wetlands-Types-

• Swamps: wetlands that contain emergent trees such as bald cypress. Ex: Okefenokee swamp (GA) and Great Dismal swamp (VA/NC)

• Marshes: contain mostly non-woody vegetation such as cattails and sedges. Most of the Florida Everglades is this type.

• Bogs: higher in acidity than other wetlands. Sphagnum moss and spruce trees are often found in bogs.

• They help reduce the severity of droughts as they receive large amounts of rainwater then slowly release it to groundwater or surface water systems.

• They help to filter pollutants from water.• They serve as migratory stops and breeding

areas for many bird species. (many of these species are endangered)

Freshwater Wetlands-Functions-

• Many wetland areas have been drained for agricultural use or development.

• Some have been drained for the purpose of reducing mosquito breeding grounds.

• An effort to offset unavoidable wetland impacts is called “wetland mitigation.” The result of this effort is to incur no net loss of wetland function by creating new wetlands, restoring previous wetlands, or protecting adjacent wetlands.

Freshwater Wetlands-Issues-

Florida Everglades1904: Napoleon Bonaparte Broward was elected Governor on the promise to create an "Empire of the Everglades," by wringing the last drop of water out of that "pestilence-ridden swamp."

1906: Dredging began on the North New River Canal, the first in south Florida's system of drainage canals

Estuaries• Areas where freshwater and salt

water meet. (the resulting mix is called “brackish water”)

• They are partially surrounded by land, and have open access to the ocean, and they have a large supply of freshwater from rivers.

• They are extremely productive ecosystems, and they contain a high species diversity.

• Salt marshes: are found along the coasts of areas with temperate climates.

• Similar to freshwater marshes, they contain non-woody emergent vegetation.

• Many are found in estuaries.• They provide habitat for spawning fish and

shellfish.

Salt Marshes

• Mangrove swamps: occur along tropical and subtropical coasts.

• They contain trees that tolerate high salinity and moisture.

• They often occur in estuaries & provide coastal protection from erosion and storm damage.

• They have soils rich in nutrients, and they are habitat to many species of fish and shellfish.

Mangrove swamps(aka: Mangroves or Mangrove forests)

• 35% of Mangroves are already gone.• The threats to mangroves may be natural:

climate change, invasive species, insectdamage.

• Or threats may be anthropogenic: urban development, overharvesting (wood), pollution, water diversion projects.

Trophic states of aquatic ecosystems

• Trophic means “nutrition” or “growth”• Oligotrophic: body of water has low nutrient

concentrations, and low plant growth• Eutrophic: body of water has high nutrient

concentrations and high plant growth.• Mesotrophic: falls between oligotrophic state

and eutrophic state.

Trophic states of aquatic ecosystems

• Factors that regulate trophic states:– Rate of nutrient supply: from human land uses,

soil type, watershed geology, vegetation– Climate: amount of sunlight, temperature,

precipitation.– Morphometry (shape of the water body’s basin):

depth, volume, surface area, watershed to surface ratio.

Trophic states of aquatic ecosystems

• Eutrophication: the progression of a body of water to a eutrophic state. (typically lakes/ponds)

• This occurs when nutrient concentrations increase in a body of water.

• It may be natural or cultural (also called artificial)– Natural Eutrophication: occurs from natural nutrient

sources (runoff from soils high in nutrients)– Cultural Eutrophication: occurs when runoff from

human activities contain high amounts of plant nutrients (such as nitrates and phosphates). Ex: livestock or crop farms, discharge from industries.

Marine ecosystems

• Oceans: help to control Earth’s climate, dilute and disperse human wastes, biogeochemical cycling (water, carbon , nitrogen, phosphorus)

• The basis of the ocean food chain is phytoplankton.

• The ocean, like bodies of freshwater, is classified into zones: Coastal, intertidal, open ocean, benthic

• Intertidal: nutrient-rich, ample light penetration, high DO. Organisms are subject to high and low tides, and wave activity.

• Coastal: also called “neritic zone” covers the continental shelf, where 90% of all ocean life exists. It is highly productive.

• Open ocean (“Oceanic” or “Pelagic zone”). The largest part of the marine environment, but the least productive. -Classified as: euphotic / photic (light penetrates)

aphotic (light does not penetrate)

Marine ecosystems- Ocean zones -

• Benthic: “ocean bottom” - In shallow areas it is highly productive. Coral reefs and kelp forests are found here, which provide habitat for a variety of marine organisms.

- In deeper areas bottom feeders consume organic matter from dead marine life.

Marine ecosystems- Ocean zones continued -

Ocean zones