Southward invasion of Craspedacusta sowerbii across mesotrophic lakes in Chile: geographical distribution and genetic diversity of the medusa phase

Craspedacusta is a freshwater jellyfish that has been introduced to Chilean lakes. Blooms of the medusa stage of Craspedacusta were first detected in an artificial water body in Valparaiso (lat 32 degrees S) in 1942. Blooms of this invasive hydroid have been observed in Andean lakes of northern Patagonia (lat 40 degrees S) ever since and at present. The main goal of this study was to deepen the knowledge of the invasion history of freshwater jellyfish in Chile. A regional survey of 65 lakes in south central Chile (lat 32-42 degrees S) showed that this jellyfish occurs most often in mesotrophic waters. We used analyses of the cytochrome oxidase subunit I (COI) gene and the small ribosomal subunit (SSU) to establish that Chilean jellyfish populations were Craspedacusta sowerbii. We also established that clonal medusa populations currently inhabit lakes from different bio-climatic zones of Southern Chile. In general, our findings support the hypothesis that all populations of C. sowerbii derive from a single introduction event of Chinese origin (podocyst or polyps) followed by an apparent southward clonal expansion across mesotrophic lakes in the country. At present, molecular information of polyp stages of C. sowerbii in Chilean lakes is nonexistent, so it is impossible to rule out the presence of either other genetic variants of Craspedacusta or other invasive hydroids. To better understand the potential impacts of this invader on local and regional aquatic biodiversity, both molecular and ecophysiological studies are needed on both polyp and medusa stages of C. sowerbii.