Aquatic Ecosystems The types of organism in an aquatic ecosystem are mainly determined by the water’s salinity. SALINITY – the amount of dissolved salts that water contains. Two types of Aquatic Ecosystems: Freshwater Ecosystems Marine Ecosystems Examples of Freshwater Ecosystems include: Lakes Ponds Freshwater Wetlands (marshes, swamps) Rivers Streams Some Biotic Factors in an Aquatic Ecosystem 1. Plankton: Organisms that cannot swim against currents, so they are drifters. Phytoplankton – drifting plants that are the food base for most aquatic ecosystems; most are microscopic. Zooplankton – drifting animals, which may be microscopic or as large as jellyfish. 2. Nekton: Free-swimming organisms. Fish, turtles, & whales. 3.Benthos: Bottom-dwelling organisms. Mussels, worms, & barnacles. Many benthic organisms live attached to hard surfaces. ORGANISMS CALLED DECOMPOSERS ARE ALSO PRESENT IN AQUATIC ECOSYSTEMS. THEY BREAK DOWN DEAD ORGANISMS. LAKES & PONDS Structured into horizontal and vertical zones o Littoral zone: nutrient rich; aquatic life is diverse and abundant; plants are rooted in the mud underwater, etc. o Benthic zone: the bottom of the pond or lake; cooler water; little sunlight; bacteria & decomposers live on dead plants and animals that drift down from above. How do nutrients affect a lake? Eutrophication is an increase in the amount of nutrients in an aquatic ecosystem. Algae and plant grow due to nutrients in a body of water. As the amount of algae and plants grow, so does the amount of bacteria and decomposers. These bacteria use the oxygen dissolved in the lake water, eventually reducing the amount available for oxygen-loving organisms. FRESHWATER WETLANDS Covered with fresh water for at least part of the year. Two types: o Marshes – contain non-woody plants, such as cattails. o Swamps – dominated by woody plants, such as trees and shrubs. MANY WETLANDS HAVE BEEN DRAINED, FILLED, OR CLEARED FOR FARMS OR RESIDENTIAL/COMMERCIAL DEVELOPMENT.