As human coastal populations increase, the runoff of sediment and agricultural chemicals has increased, too, causing some of the once-clear tropical waters to become cloudy. At the same time, overfishing of popular fish species has allowed the predator species that eat corals to go unchecked.
When change occurs rapidly, species can become extinct before evolution leads to new adaptations. Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted brackish saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives.
Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies and is based on the rate of flow of its freshwater sources. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water. The short-term and rapid variation in salinity due to the mixing of fresh water and salt water is a difficult physiological challenge for the plants and animals that inhabit estuaries.
Many estuarine plant species are halophytes : plants that can tolerate salty conditions. Halophytic plants are adapted to deal with the salinity resulting from saltwater on their roots or from sea spray. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs. Other plants are able to pump oxygen into their roots.
Animals, such as mussels and clams phylum Mollusca , have developed behavioral adaptations that expend a lot of energy to function in this rapidly changing environment. When these animals are exposed to low salinity, they stop feeding, close their shells, and switch from aerobic respiration in which they use gills to anaerobic respiration a process that does not require oxygen. When high tide returns to the estuary, the salinity and oxygen content of the water increases, and these animals open their shells, begin feeding, and return to aerobic respiration.
Freshwater biomes include lakes and ponds standing water as well as rivers and streams flowing water.
They also include wetlands, which will be discussed later. Humans rely on freshwater biomes to provide aquatic resources for drinking water, crop irrigation, sanitation, and industry. These various roles and human benefits are referred to as ecosystem services. Lakes and ponds are found in terrestrial landscapes and are, therefore, connected with abiotic and biotic factors influencing these terrestrial biomes. Lakes and ponds can range in area from a few square meters to thousands of square kilometers.
Temperature is an important abiotic factor affecting living things found in lakes and ponds. In the summer, thermal stratification of lakes and ponds occurs when the upper layer of water is warmed by the sun and does not mix with deeper, cooler water.
Light can penetrate within the photic zone of the lake or pond. Phytoplankton small photosynthetic organisms such as algae and cyanobacteria that float in the water are found here and carry out photosynthesis, providing the base of the food web of lakes and ponds.
Zooplankton very small animals that float in the water , such as rotifers and small crustaceans, consume these phytoplankton.
At the bottom of lakes and ponds, bacteria in the aphotic zone break down dead organisms that sink to the bottom. Nitrogen and phosphorus are important limiting nutrients in lakes and ponds. Because of this, they are determining factors in the amount of phytoplankton growth in lakes and ponds. When there is a large input of nitrogen and phosphorus from sewage and runoff from fertilized lawns and farms, for example , the growth of algae skyrockets, resulting in a large accumulation of algae called an algal bloom.
Algal blooms Figure 4 can become so extensive that they reduce light penetration in water. As a result, the lake or pond becomes aphotic and photosynthetic plants rooted in the lake bottom cannot survive. When the algae die and decompose, severe oxygen depletion of the water occurs. Fishes and other organisms that require oxygen are then more likely to die, and resulting dead zones are found across the globe.
Neretic Zone: the water overlying the continental shelf. With the exception of Antarctica, these waters usually extend to a depth of ft. Sunlight penetrates the entire water column. Oceanic Zone: The region of the sea extending from the edge of the continental shelf, over the continental slope, and over ocean floor. It is characterized by darkness and tremendous pressure. Vertical life zones are significant here.
Euphotic zone : The top of the water column as far down as light is available for photosynthesis. Depending upon water clarity, the bottom of the euphotic zone is about ft below sea level. Also known as epipelagic zone. When a predator is looking at them from below, they blend into the lighter waters above. Entering the Twilight Zone Animals that live in the twilight zone must be able to survive cold temperatures, an increase in water pressure and dark waters.
There are no plants in this zone, because there is not enough light for photosynthesis. Octopus, squid, and the hatchet fish are some of the animals that can be found in this zone. Many animals in this zone have thin bodies that help them hide from predators. Other organisms in this zone are red or black in color to better blend in with the dark water. When a predator is looking up at them, they are so thin that they are hard to see!
Some fish, like viper fish and the hatchet fish, have sharp fangs and large mouths that help them catch food. Other fish have large eyes that help them see in the dark waters. Most of the fish in this zone don't chase their food.
The neritic zone is from low tide mark and slopes gradually downward to the edge of the seaward side of the continental shelf. Some sunlight penetrates to the seabed here. The oceanic zone is the entire rest of the ocean from the bottom edge of the neritic zone, where sunlight does not reach the bottom.
Skip to main content. Oceans and Coastal Environments. Search for:.
0コメント