| Summary: | Interactions between native and introduced species are complex , multifaceted , and can have cascading effects throughout an ecosystem. While scientists have taken great strides to understand how these dynamics change with the introduction of a novel species , less work has been done to explore how native and introduced species interactions change in the face of parasitism. I investigated these interactions using three intertidal crab species in the Western North Atlantic; the native rock crab Cancer irroratus , the introduced European green crab , Carcinus maenas , and the introduced Asian shore crab , Hemigrapsus sanguineus along with a parasitic trematode Micropahllus spp. C. maenas and C. irroratus are both hosts to microphallid trematode parasites in the Western North Atlantic , but little is known about microphallid infections in H. sanguineus in this region. In order to properly evaluate infection in these crabs , I conducted two surveys along the New England coast to determine prevalence of infection in these three species. I utilized genetic tools to determine if the microphallids infecting these crabs are native to Western North Atlantic , potentially introduced from Europe with C. maenas , or a combination of both. During these surveys , I found all three crab species to be infected with one or more trematode parasites along the Western North Atlantic. Genetic analyses show that there are at least four distinct lineages of trematodes infecting crabs collected in this region , two of which matched previously identified trematodes in the region , Microphallus similis and Gynaecotyla adunca. In conjunction with determining which parasites are infecting these crabs , I wanted to determine what effects infection had on these different host species. To understand the effects of infection I conducted both physiological assays on crabs collected during the survey , analyzing Hepatosomatic and Gonadosomatic indices (HSI and GSI) as well as infection experiments on the two introduced crabs , C. maenas and H. ...
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