Aquatic Ecosystems make up most of the Biosphere

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Aquatic Ecosystems make up most of the Biosphere

• 34.4

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Ponds and Lakes

• Freshwater ecosystems include water bodies with
  very little dissolved salt, such as most ponds,
  lakes, streams, and rivers.
• Ponds and lakes are standing (not flowing) bodies
  of water.

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• Lakes and large ponds are divided into zones
  based on water depth and distance from shore.
• The shallow water close to shore and the upper
  zone of water away from shore make up the photic
  zone, so named because light is available for
  photosynthesis.

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• Phytoplankton, microscopic algae and
  cyanobacteria that carry out photosynthesis, live
  in the photic zone, along with water plants.
• The deep, murky areas of a lake, where light
  levels are too low to support photosynthesis, are
  called the aphotic zone.

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• The bottom of any aquatic ecosystem is called the
  benthic zone.
• The benthic zone consists of rock, sand, and
  sediment.
• The organisms of deep (aphotic) benthic areas
  feed on wastes that sink down from the photic
  zone.

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Streams and Rivers

• A body of flowing fresh water is known as a
  stream or a river.
• A river changes greatly between its source and
  the point at which it empties into a lake or the
  ocean.
• Near the source, the water is usually cold, low
  in nutrients, and clear.

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• Few phytoplankton inhabit this part of a river.
• Instead, the major producers near a river's
  source are algae attached to rocks on the river
  bed.
• Many species of arthropods live in the benthic
  zone, feeding on algae, fallen leaves, and one
  another.

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• Downstream from its source, a river generally
  becomes wider and deeper.
• Marshes and other wetlands are common in these
  downstream areas.
• The water is usually warmer and murkier than it
  is upstream.
• More phytoplankton live in this part of a river.

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Estuaries

• Streams and rivers merge with ocean water in
  areas known as estuaries.
• Estuary organisms experience changes in salt
  concentration and temperature as the fresh water
  and salt water mix.
• Estuaries serve as breeding grounds for many
  invertebrate and fish species, and as nesting and
  feeding areas for a great diversity of birds.

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• Along most of the east coast of the United
  States, the major ecosystems found in estuaries
  are salt marshes.
• In tropical areas, the typical estuary ecosystems
  are mangrove swamps.
• These swamps are dominated by mangrove trees,
  which are anchored by tangled networks of arching
  roots.

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Ocean Zones

• Zones of depth include the benthic zone, or ocean
  floor, and the pelagic zone, or open water above
  the ocean floor.
• Also as in freshwater ecosystems, the ocean has a
  photic zone, which receives enough sunlight to
  support photosynthesis, and a dark aphotic zone.
• Zones of distance from shore include the
  intertidal zone, neritic zone, and oceanic zone.

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Intertidal Zone

• The area of shore between the high-tide and
  low-tide lines is called the intertidal zone.
• Pounded by waves during high tide and exposed to
  the sun and drying winds during low tide, benthic
  organisms in this zone must be well-adapted to
  survive these harsh conditions

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Neritic Zone

• The area of the ocean from the low-tide line out
  to the edge of the continental shelf is the
  neritic zone.
• Since the ocean here is fairly shallow, some
  sunlight reaches the bottom in most of the
  neritic zone.
• As a result, many organisms that require light
  for photosynthesis can live in this zone,
  including seaweeds and phytoplankton.

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Oceanic Zone

• The vast open ocean from the edge of the
  continental shelf outward is called the oceanic
  zone.
• Phytoplankton drifting in the photic layer are
  the major producers in this zone.
• Microscopic animals called zooplankton also
  inhabit the photic zone and in turn are a source
  of food for other animals.

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Coral Reefs

• All the invertebrate phyla are found on coral
  reefs, including sponges, sea anemones, worms,
  sea stars, and mollusks.
• Vertebrates such as sea turtles and fishes also
  roam the reefs.
• Most reefs are formed by colonies of coral
  polyps, animals in the phylum Cnidaria that
  secrete hard external skeletons.

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Deep-sea Vents

• Imagine the surprise of biologists when they
  first glimpsed giant tube worms living at depths
  of 2,500 meters.
• These unfamiliar organisms live around deep-sea
  hydrothermal vents, spots on the ocean floor
  where hot gases and minerals escape from Earth's
  interior into the water.

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• No sunlight reaches this deep, dark zone.
• The vent communities use the chemical energy from
  Earth's interior as their energy source.
• The producers in these ecosystems are prokaryotes
  that, instead of carrying out photosynthesis, can
  extract energy from sulfur compounds spewing from
  the vents and use this energy to make
  carbohydrates.