Didemnum vexillum: Identity, Origin, and Life History of an Invasive Ascidian

Date of Completion

January 2012


Biology, Ecology|Biology, Evolution and Development|Biology, Oceanography




Over the past forty years, an increasing number of previously unrecorded populations of a colonial ascidian belonging to the genus Didemnum have been documented in most temperate coastal regions of the world, impacting aquaculture operations, natural rocky habitats, cobble/gravel substrates, and eelgrass beds. Recent morphological analyses identified the populations as Didemnum vexillum Kott, 2002. However, because of incomplete historical records and the numerous mis-identifications of this species, the native range of D. vexillum has not been conclusively known. Also, little is known about the life history cycle, population biology, and native ecology of the species. The goals of this dissertation are four-fold. First, support the morphological identification of D. vexillum using molecular characters. Second, use population genetics to determine the native region of this now cosmopolitan species. Third, describe observations on the distribution and ecology of D. vexillum in Japan, a region where there is a dearth of information on the species. And fourth, quantify aspects of D. vexillum's life history cycle to examine the relative importance of sexual and asexual pathways to reproduction and dispersal of D. vexillum.^