11/21/2023 0 Comments Zebra mussels on floatWithin 2-3 weeks, the veligers begin to ‘settle-out’ in the water under the weight of their forming shells and attach to firm, underwater surfaces. In approximately two days, the fertilized eggs develop into free-swimming larvae called veligers, which can be transported over long distances by water currents. Each year, a mature female zebra mussel may release up to one million eggs, while the male may release more than two hundred million sperm into the water where fertilization takes place. On average, zebra mussels live 2-5 years and can reproduce by their second year. More light allows for more plant growth, which provides more shelter for the organisms that the fish like to eat. Scientists believe the improved water clarity from the excess filtration allows more sunlight to reach rooted plants. However, some organisms have benefited from the arrival of zebra mussels, such as the fish that live in the vegetated shallows of the river, like the redbreasted sunfish. In addition to indirect effects from ecological changes, zebra mussels have caused direct economic damage by attaching to hard substrates like drinking water intake pipes and power plant equipment. Dissolved oxygen levels have decreased, which can have different effects on different species. Other animals, including fish like shad and herring that live in the open water, have also suffered. Many native mussel populations have decreased to the point of being threatened or endangered, because they are out-competed by the zebra mussels. Companies that use Hudson River water spend a lot of money to ensure that their pipes remain clear of zebra mussels. Once zebra mussels are attached to a surface in an ideal environment, they multiply rapidly and form densely-packed colonies. Water intake pipes provide an ideal habitat for the zebra mussel because they provide both protection and a constant flow of water, and, hence a constant food supply. This means there is a lot less food available for fish, native mussels, and other river animals. Microzooplankton, like the rotifer pictured below, have declined by 70%, while phytoplankton have decreased by 80%. These mussels were most likely brought to those areas by careless human activity.Īs a result of the zebra mussels’ huge appetite, populations of plankton in the Hudson River have fallen sharply. Notice the stars in the middle of the country, indicating new invasion areas. Look at the map below to see where the zebra mussel (in red), and its similarly invasive relative, the quagga mussel (in green), have been found. The food web changes that the mussel has caused compare in magnitude to disturbances in other aquatic ecosystems caused by toxins, nutrient pollution, or acid rain. The zebra mussel invasion has had profound effects on the Hudson River ecosystem. Phytoplankton and zooplankton form the base of the aquatic food web, so many animals depend on them for survival. Zebra mussels are suspension feeders, eating phytoplankton, small zooplankton, large bacteria, and organic detritus by filtering the water and straining out the edible material. ![]() While some aspects of filtering the water are positive, the words “filter” and “clean” are not synonymous. Since there are so many of them, they are able to filter all of the water in the freshwater portion of the Hudson River every 2-4 days! Before the invasion, the native mussels filtered the water only every 2-3 months. Their densities can reach over 100,000 individuals per square meter. By the end of 1992, they had spread throughout the river, and their biomass was greater than the combined biomass of all other consumers (fish, zooplankton, zoobenthos, bacteria) in the river. Zebra mussels were first discovered in the Hudson at very low densities in 1991. They are very efficient filter-feeders, which means that they filter small organisms and organic particles out of the water at very high rates. Zebra mussels will eventually colonize most of the waters in North America except for places that are too saline or too warm for their survival. They rapidly became established in the Great Lakes and the waters draining them. Zebra mussels reached North America in the mid-1980s in the ballast water of a ship. The zebra mussel ( Dreissena polymorpha) is a small bivalve originally native to the Caspian Sea region.
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