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By the end of this section, you will be able to:
  • Describe the effects of abiotic factors on the composition of plant and animal communities in aquatic biomes
  • Compare and contrast the characteristics of the ocean zones
  • Summarize the characteristics of standing water and flowing water freshwater biomes

Abiotic factors influencing aquatic biomes

Like terrestrial biomes, aquatic biomes are influenced by a series of abiotic factors. The aquatic medium—water— has different physical and chemical properties than air, however. Even if the water in a pond or other body of water is perfectly clear (there are no suspended particles), water, on its own, absorbs light. As one descends into a deep body of water, there will eventually be a depth which the sunlight cannot reach. While there are some abiotic and biotic factors in a terrestrial ecosystem that might obscure light (like fog, dust, or insect swarms), usually these are not permanent features of the environment. The importance of light in aquatic biomes is central to the communities of organisms found in both freshwater and marine ecosystems. In freshwater systems, stratification due to differences in density is perhaps the most critical abiotic factor and is related to the energy aspects of light. The thermal properties of water (rates of heating and cooling) are significant to the function of marine systems and have major impacts on global climate and weather patterns. Marine systems are also influenced by large-scale physical water movements, such as currents; these are less important in most freshwater lakes.

The ocean is categorized by several areas or zones ( [link] ). All of the ocean’s open water is referred to as the pelagic realm    (or zone). The benthic realm    (or zone) extends along the ocean bottom from the shoreline to the deepest parts of the ocean floor. Within the pelagic realm is the photic zone    , which is the portion of the ocean that light can penetrate (approximately 200 m or 650 ft). At depths greater than 200 m, light cannot penetrate; thus, this is referred to as the aphotic zone    . The majority of the ocean is aphotic and lacks sufficient light for photosynthesis. The deepest part of the ocean, the Challenger Deep (in the Mariana Trench, located in the western Pacific Ocean), is about 11,000 m (about 6.8 mi) deep. To give some perspective on the depth of this trench, the ocean is, on average, 4267 m or 14,000 ft deep. These realms and zones are relevant to freshwater lakes as well.

Art connection

 The illustration divides the ocean into different zones based on depth. The top layer, called the photic zone, extends from the surface to 200 m. The aphotic zone extends from 200 to 4,000 m. They abyssal zone extends from 4,000 m to the ocean bottom. The ocean is also divided into zones based on distance from the shore. The intertidal zone extends from high to low tide. The neritic zone extends from the intertidal zone to the point at which ocean depth is about 200 m. At about this depth, the continental shelf ends in a steep slope to the ocean bottom. The oceanic zone is the area of open ocean. A thin section of the oceanic zone extending from top to bottom and adjacent to the continental shelf is labeled the benthic realm. All of the ocean’s open water is referred to as the pelagic realm, which is labeled on the left.
The ocean is divided into different zones based on water depth and distance from the shoreline.

In which of the following regions would you expect to find photosynthetic organisms?

  1. the aphotic zone, the neritic zone, the oceanic zone, and the benthic realm
  2. the photic zone, the intertidal zone, the neritic zone, and the oceanic zone
  3. the photic zone, the abyssal zone, the neritic zone, and the oceanic zone
  4. the pelagic realm, the aphotic zone, the neritic zone, and the oceanic zone

Marine biomes

The ocean is the largest marine biome. It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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