Aquatic Biomes
LakesPhysical Environment: Standing bodies of water ranging from ponds (few square meters in area) to lakes (thousands of square kilometers). Stratification created as light decreases with depth. Temperate lakes have seasonal thermocline while tropical lowland lakes have thermocline year round.
Chemical Environment: Salinity, oxygen concentration, and nutrient content differ among lakes and vary with season. Oligotrophic lakes are nutrient poor and generally oxygen rich. Eutrophic lakes are the opposite- nutrient rich and have lack of oxygen. Amount of decomposable organic matter is low in oligotrophic lakes but high in eutrophic lakes. High decomposition rate causes periodic oxygen depletion in eutrophic lakes. Geologic Features: Oligotrophic lakes become more eutrophic as runoff adds sediment and nutrients. Oligotrophic lakes have less surface area than eutrophic. Photosynthetic Organisms: Rooted and floating aquatic plants live in the littoral zone (shallow, well-lit waters close to shore). The limnetic zone (water is too deep to support rooted aquatic plants here; farther from shore) contains a variety of phytoplankton, including cyanobacteria. Heterotrophs: Limnetic zone- small drifting heterotrophs (zooplankton) graze on phytoplankton. Benthic zone- contains assorted invertebrates whose species composition depends on oxygen levels. Fish live in all zones with an abundance of oxygen. Human Impact: Runoff from fertilized land and dumping of waste result in nutrient enrichment- can produce algal blooms, oxygen depletion, and fish deaths. |
WetlandsPhysical Environment: Wetland- a habitat that is inundated by water at least some of the time and that supports plants adapted to water-saturated soil. Some wetlands are always inundated, while some flood.
Chemical Environment: Because of high organic production by plants and decomposition by microbes, etc., both water and soil are periodically low in dissolved oxygen. Wetlands have a high capacity to filter dissolved nutrients and chemical pollutants. Geologic Features: Basin wetlands develop in shallow basins, ranging from upland depressions to filled-in lakes and ponds. Riverine wetlands develop along shallow and periodically flooded banks and rivers and streams. Fringe wetlands occur along coasts of large lakes and seas, where water flows because of rising lake levels or tidal action; include freshwater and marine biomes. Photosynthetic Organisms: One of the most productive biomes. Their water-saturated soils favor the growth of plants- floating pond lilies, emergent cattails, sedges, tamarack, black spruce- which have adaptations that enable them to grow in water or in soil that is periodically anaerobic owing to the presence of unaerated water. Woody plants dominate the vegetation of swamps. Bogs are dominated b sphagnum mosses. Heterotrophs: Home to a diverse community of invertebrates, birds, etc. Herbivores, fro crustaceans and aquatic insect larvae to muskrats, consume algae, detritus, plants. Carnivores are varied- dragonflies, otters, frogs, alligators, herons. Human Impact: Draining and filling destroy up to 90% of wetlands- help purify and reduce peak flooding. |
Streams and RiversPhysical Environment: Currents. Headwater streams are cold, clear, turbulent, swift. Farther downstream, where many tributaries may have formed a river, the water is warmer and more turbid because of suspended sediment. Streams and rivers are stratified into vertical zones.
Chemical Environment: Salt and nutrient content of streams and rivers increases from headwaters to the mouth. Headwaters are oxygen rich. Downstream water have oxygen, except where there has been organic enrichment. Large fraction of the organic matter in rivers consist of dissolved or highly fragmented material that is carried by the current from forested streams. Geologic Features: Headwater stream channels are narrow, have rocky bottom, and alternate between shallow sections and deeper pools. Downstream stretches of rivers are wide and meandering. River bottoms are silty from sediments deposited over time. Photosynthetic Organisms: Headwater streams that flow through grasslands or deserts are rich in phytoplankton or rooted aquatic plants. Heterotrophs: Diversity of fishes and invertebrates inhabit unpolluted rivers and streams, distributed according to and throughout vertical zones. In streams flowing through temperate or tropical forests, organic matter from terrestrial vegetation is the source of food fort aquatic consumers. Human Impact: Municipal, agricultural, and industrial pollution degrade water quality and kill aquatic organisms. Damming and flood control impair natural functioning of stream and river ecosystems and threaten migratory species. |
EstuariesPhysical Environment: Estuary- a transition area between river and sea. Seawater flows up estuary channel during rising tide and flows back down during falling tide. High-density seawater occupies the bottom of the channel and mixes little with low-density river water at the surface.
Chemical Environment: Salinity varies spatially within estuaries, from that of fresh water to that of seawater; varies with the rise and fall of tides. Nutrients from the river make estuaries, like wetlands, among the most productive biomes. Geologic Features: Estuarine flow patterns combined with sediments carried by river and tidal waters create complex network of tidal channels, islands, natural levees, and mudflats. Photosynthetic Organisms: Saltmarsh grasses and algae, and phytoplankton are the producers. Heterotrophs: Estuaries support worms, oysters, crabs, and many fish species that humans consume. Marine invertebrates and fishes use estuaries as breeding ground or migrate through them to freshwater habitats upstream. Estuaries are crucial feeding areas for waterfowl and marine animals. Human Impact: Filling, dredging, pollution from upstream disrupt estuaries worldwide. |
Intertidal ZonesPhysical Environment: An intertidal zone is periodically submerged and exposed by the tides, twice daily on marine shores. Upper zones experience longer exposures to air and variations in temperature and salinity. Changes in physical conditions from upper to lower intertidal zones limit the distributions of organism to a particular strata.
Chemical Environment: Oxygen and nutrient levels are high and renewed with each turn of the tides. Geologic Features: The substrates of intertidal zones, generally either rocky or sandy, selects particular behavior and anatomy among intertidal organisms. The configuration of bays or coastlines influences the magnitude of the tides and the exposure of wave action to intertidal organisms. Photosynthetic Organisms: A high diversity and biomass of attached marine algae inhabit rocky intertidal zones (especially lower zones). Sandy intertidal zones exposed to wave action lack attached plants and algae, while sandy zones in protected bays or lagoons support seagrass and algae. Heterotrophs: Many animals in rocky intertidal zones have structural adaptations that enable them to attach to the hard substrate. Composition, density, and diversity of animals change from upper to lower intertidal zones. Many animals in sandy or muddy intertidal (worms, clams, and predatory crustaceans) bury themselves and feed as tides bring food. Other common animals: sponges, sea anemones, echinoderms, and small fishes. Human Impact: Oil pollution and construction of rock walls and barriers to reduce erosion from waves and storm surges have disrupted these zones. |
Ocean Pelagic ZonesPhysical Environment: Oceanic pelagic zone is a realm of water, constantly mixed by wind-driven oceanic currents. Because of higher water clarity, the photic zone extends to greater depths than in coastal marine waters.
Chemical Environment: Oxygen levels are high. Nutrient concentrations are lower than in coastal waters. Because they are thermally stratified year round, some tropical areas of the oceanic pelagic zone have lower nutrient concentrations than temperate oceans. Turnover between fall and spring renews nutrients in the photic zones of temperate and high-latitude ocean areas. Geologic Features: This biome covers 70% of Earth's surface and has an average depth of 4,000 m. The deepest point in the ocean is more than 10,000 m beneath the surface. Photosynthetic Organisms: Phytoplankton, including photosynthetic bacteria that drift with the oceanic currents. Spring turnovers renews nutrients in temperate oceans producing a surge of phytoplankton growth. Because of the large extent of this biome, photosynthetic plankton account for half of the photosynthetic activity on Earth. Heterotrophs: Most abundant heterotroph is the zooplankton. These protists, worms, copepods, shrimp-like krill, jellies, and small larvae of invertebrates and fishes feed on photosynthetic plankton. Includes free-swimming animals (large squids, fishes, sea turtles, and marine animals). Human Impact: Overfishing depletes fish stocks in all Earth's oceans, which have been polluted by waste dumping. |
Coral ReefsPhysical Environment: Coral reefs are formed from calcium carbonate skeletons of corals. Shallow reef-building corals live in photic zones of stable tropical marine environments with high water clarity (islands and edges of continents). Sensitive to temperatures below 18-20 degrees C and above 30 degrees C. Deep-sea coral reefs are less known than their shallow counterparts but harbor diversity.
Chemical Environment: Corals require high oxygen levels and are excluded by inputs of fresh water and nutrients. Geologic Features: Corals require solid substrate for attachment. Coral reefs begin as fringing reef on an island, forming an offshore barrier reef later and becoming a coral atoll as the older island submerges. Photosynthetic Organisms: Unicellular algae live within tissues of corals, forming a mutualistic relationship because it provides the corals with organic molecules. Multicellular red and green algae growing on the reef contributes amounts of photosynthesis. Heterotrophs: Coral are the predominant animals on coral reefs. Fish and invertebrate diversity is also high. Human Impact: Collecting of coral skeletons and overfishing reduces the population of corals and reef fishes. Global warming and pollution may be contributing to coral death. Development of coastal mangroves for aquaculture has reduced spawning grounds for reef fishes. |
Marine Benthic ZonePhysical Environment: The marine benthic zone consists of seafloor below the surface waters of the coastal/neritic zone and the offshore pelagic zone. Receives no sunlight. Water temperature declines with depth, but pressure increases. As a result, organisms deep in this zone are adapted to cold and very high water temperatures.
Chemical Environment: Except in areas of organic enrichment, oxygen is present at sufficient concentrations. Geologic Features: Soft sediments cover most of this zone. However, there are rocky substrates on reefs, submarine mountains, and new oceanic crust. Photosynthetic Organisms: Photosynthetic organism, mainly seaweeds and filamentous algae, are limited to shallow benthic areas with light. Unique assemblages of organisms are found near deep sea hydrothermal vents on mid-ocean ridges. In dark, hot environments, the producers are chemoautotrophic prokaryotes that obtain energy from oxidizing H2S formed by a reaction of the hot water with dissolved sulfate. Heterotrophs: Neritic benthic communities include numerous invertebrates and fishes. Beyond the photic zone, consumers depend on organic matter. Among animals of the deep-sea hydrothermal vent communities are tube worms, nourished by chemoautotrophic prokaryotes that are symbionts within their bodies. Other invertebrates, arthropods and echinoderms, are abundant around the hydrothermal vents. Human Impact: Overfishing has wiped out important benthic fish populations. Dumping of organic wastes has created oxygen-deprived benthic areas. |