Impact of Asian Clams (Corbicula fluminea) on on Unionidae, or the family of pearly freshwater mussels


Corbicula fluminea is a species of freshwater clam that is native to eastern Asia and has become an extraordinarily successful invader of freshwater ecosystems and is found on every continent except for Antarctica (Leff et al., 1990; Hornbach, 1992; Karatayev et al., 2007; Lucy & Graczyk, 2008; Sousa et al., 2008a; Crespo et al., 2015). It is widely theorized they were introduced as a food source on the west coast of the United States and were first discovered in the country in 1938 (Sinclair & Isom, 1963; Counts, 1981). Impressivly, C. fluminea have the highest secondary production values ever measured for a species colonizing a freshwater ecosystem and the highest record net productivity for any bivalve (McMahon, 2002; Sousa et al., 2008b). While there are multiple species of Corbicula that are invading aquatic systems, the most common species is C. fluminea (Renard et al., 2000; Siripattrawan et al., 2000). There are several factors that have led to successful invasions of C. fluminea including high fecundity, functional hermaphroditism, self-fertilization, rapid sexual maturity, lack of a parasitic life stage, pedal feeding (that is feeding via the cilia on the foot) and filter feeding, and the ability to disperse across long distances (McMahon, 2002).

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Impacts of climate change on the Great Lakes

The Great Lakes contain 20 percent of the world’s freshwater (McBean 2008) and are already facing the impacts of anthropogenic climate change. The Greats Lakes have seen a 10 to 25 percent increase in precipitation from 1981 to 2010 (NOAA, 2019) due to increased evaporation. The amount of precipitation is predicted to increase by 12.5 percent by 2080 (Wang 2016). Increased rainfall has led to increased nutrients washed out of soils, as found in two studied watersheds (Wang 2018). In one watershed the amount of phosphorus washed out, due to soil erosion, could increase by 108 percent by 2099 (Ibid). These additional nutrients can result in nutrient loading and therefore algae booms and eutrophication in the Great Lakes.

One reason for the increased precipitation is the reduction in ice cover, which results in more evaporation. Ice cover has decreased by 71 percent on the Great Lakes from 1973 to 2010 (Collingsworth, 2017). Many commercially important fish species allow their eggs to overwinter below the ice, with reduced ice cover their eggs are more susceptible to wave action damage (Ibid). Models to predict how much ice coverage will be reduced vary widely but they all agree that the coverage will reduce by 2050. One initial benefit of reduced ice cover is that it will reduce the number of winter kills as there will be more circulation of oxygen.

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How will climate change impact amphibians? (focus on fungal disease)

Chytridiomycosis is a disease that is killing amphibians worldwide at alarming rates. To read more about amphibians see this blog post. The disease is caused by Batrachochytrium dendrobatidis or Bd for short. Bd is a fungus that is specific to amphibians. Currently, the disease is responsible for the greatest disease-caused loss of biodiversity in recorded history. Species have had massive drops in populations and seem to have disappeared overnight.Bd occurs inside the cells of the outer skin layer. It causes microscopic changes in the skin and enlarges this layer. This is deadly because amphibians absorb water and salts through the skin. In the family of lungless salamanders, and one lungless species of caecilian Bd causes them to suffocate. Bd travels into the mouthparts of tadpoles or other larval amphibians. When tadpoles change into adults the infection spreads to the skin. Spores, which are the reproductive part of the fungus, cause the skin to become enlarged. This reduces osmotic regulation and electrolyte blood levels drop which leads to cardiac arrest. Chytridiomycosis has almost a 100 percent mortality rate.

 

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Cells infected with Batrachochytrium dendrobatidis 

 

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