Aquatic Biomes Earth's Aquatic Biomes Aquatic biomes cover approximately three-fourths of the Earth's surface and are connected to terrestrial and other aquatic biomes through the water cycle. The water cycle is a continuous succession of evaporation and condensation that controls the circulation of water between the atmosphere and biomes. Approximately 1.5% of the global precipitation, which enters terrestrial biomes as rain or snow, is stored in the ground water of terrestrial biomes. Ecologists divide aquatic biomes into two major categories: freshwater and marine. Freshwater biomes, or surface water, make up less than 1% of the Earth's water supply and 0.3% of the total supply of fresh water. Marine biomes, of which there are many types, hold 97% of the Earth's water. Principles of Biology

Aquatic Biomes Chemical and physical differences characterize aquatic biomes and their zones. Ecologists use chemical and physical differences to distinguish aquatic biomes. Water can be fresh or saline, which refers to its salinity (salt content). Aquatic biomes can range in salinity from 0.03% to 30%, but aquatic organisms typically tolerate a narrow range of salinity. Topography determines where water accumulates to form bodies of continually flowing and standing water in a region. Water chemistry and the physical characteristics of an aquatic biome are equally important in determining the type of aquatic biome in a region. The physical characteristics of an aquatic biome are primarily determined by the climate and geography of the region. Climate determines whether precipitation is in the form of rainfall or snow melt. The topography and geology of a region establish the runoff patterns that provide water for aquatic biomes. Most aquatic biomes are chemical and physically divided into layers that give different depths of the water unique characteristics, a feature called stratification. The amount of light penetrating the water in an aquatic biome forms two zones common to most deep aquatic biomes: the photic zone and aphotic zone. Only the photic zone, not the aphotic zone, has enough light for photosynthesis. A temperature stratification called the thermocline is determined by climate and depth of the aquatic biome. Temperature changes dramatically from one layer to the next; all aquatic biomes have a bottom surface called the benthic zone, which is typically covered with rock and soil. The water column of aquatic biomes can be divided into inshore and offshore zones that are named differently for each aquatic biome. An inshore zone is the boundary between the aquatic and nearby terrestrial biome. The offshore region is the open water area away from the shore. Principles of Biology

Aquatic Biomes Figure 1 Salt farms. The Great Salt Lake in Utah is a major source of table salt because of its high salinity. It is an unusual aquatic biome because it has the geographic structure of a freshwater biome but the salinity of a marine biome. Principles of Biology

Aquatic Biomes Freshwater biomes include lakes, wetlands, and rivers. Freshwater biomes are typically inland and include lakes, rivers, and wetlands. A lake is a large nonflowing body of water surrounded by land. Ecologists use the term lentic to describe still bodies of water. Most lakes have distinct stratification zones. The shoreline of a lake is called the littoral zone and typically contains plants rooted in the benthic zone. The open area of a lake is called the limnetic zone. A region of the limnetic zone where light penetrates poorly, if at all, is called the profundal zone. Principles of Biology

Aquatic Biomes Figure 2 Aquatic biome zones. Aquatic biomes are divided into zones that each have characteristic organisms. Principles of Biology

Aquatic Biomes Freshwater biomes include lakes, wetlands, and rivers. Wetlands are areas of land saturated with water most of the year. Marshes and swamps are examples of wetlands. Most wetlands have little or no water flow. Rivers are flowing bodies of water bordered by land. The term lotic is used to describe moving bodies of water. Rivers start at a region called the headwaters, which is fed fresh water by lakes, rain, runoff, and snow melt. Rivers end at a region called the mouth, which can drain into other rivers, lakes, or the ocean. The stratification of a river is divided into the aquatic-where the water flows-and the riparian-the shoreline and nearby saturated soil-zones. Sunlight typically reaches most of a river's depth unless there is much sediment. Rivers are most affected by our great need for fresh water used for agricultural operations, household purposes, and industrial application. Principles of Biology

Aquatic Biomes Marine biomes include estuaries, intertidal zones, coral reefs, and open oceans. Marine biomes are the largest of the Earth's biomes and likely contain most of the biodiversity. Marine biomes are characterized by their large size, high salinity, and tides influenced by gravitational attractive forces between the Earth and its moon. The major marine biomes are estuaries, intertidal zones, coral reefs, and open oceans. An estuary is the mouth of river where it meets an open ocean. Estuaries are formidable environments because of the high fluctuations in salinity. Important food animals, including carp, lobsters, mussels, oysters, and shrimp, thrive in estuaries. The intertidal zone is a harsh environment that undergoes long periods of drying and flooding. The intertidal zone is a biome that borders the coastlines of oceans between the high and low tides. Estuary and intertidal biomes are both sensitive environments that are being disrupted by many human activities and pollution. Principles of Biology

Aquatic Biomes Figure 3 Fragile intertidal biomes. Intertidal biomes are commonly used for beachside living, fishing, and recreation. Many cities also divert sewage and wastewater into these biomes. Principles of Biology

Aquatic Biomes Marine biomes include estuaries, intertidal zones, coral reefs, and open oceans. Oceans have the largest volume of water of any aquatic biomes. Oceans' salinity is fairly constant, but temperatures vary gradually with climate, light penetration, and depth. The inshore region of an ocean is the neritic zone, which borders an intertidal biome. Sunlight completely penetrates the neritic zone and provides conditions for an abundance of aquatic organisms. The open water region of the ocean is called the oceanic zone and its full depth is called the pelagic zone. Some benthic ocean regions are associated with underwater volcanoes called deep sea vents. Much of the benthic zones in warm oceans are built on the calcium carbonate skeletons of corals, marine animals related to jellyfish. Coral reefs are typically restricted to the photic zone of tropical oceans where there is little sediment in the water. Over time, some coral reefs form islands called atolls. An atoll is a coral island that completely or partially encircles a lagoon. Unfortunately, global climate change, pollution, and acid precipitation are threatening coral reefs throughout the world. Principles of Biology

Aquatic Biomes Figure 4 Factors affecting Vibrio seasonality. Plankton composition and environmental factors contribute to Vibrio seasonality. Principles of Biology