Fragment reattachment, reproductive status, and health indicators of the invasive colonial tunicate Didemnum vexillum with implications for dispersal
The invasive colonial tunicate Didemnum vexillum is now widespread in coastal and offshore waters of New England, USA. D. vexillum can inflict ecological and economic damage through biofouling and habitat modification. Natural and anthropogenic processes that fragment colonies of D. vexillum may be accelerating the spread of this invader. Reattachment success and fragment viability were confirmed in the laboratory after four weeks of suspension in experimental aquaria. The shape of suspended D. vexillum fragments progressed from flattened to globular spheres and then flattened again after reattachment to the substrate. Reproductive activity, confirmed by the presence of eggs and larvae, was observed for fragments suspended up to 3 weeks suggesting that D. vexillum is capable of reproducing while in a fragmented, suspended state. An index of colony health was used to monitor change in D. vexillum health while in suspension. Overall, colony health declined with time in suspension although colonies that appeared dead (black and gray in overall color) still contained a substantial number of healthy live zooids. These results suggest that activities that cause fragmentation can significantly facilitate the spread of D. vexillum. Coastal managers should consider reducing or eliminating, when practical, activities that return fragmented colonies of D. vexillum to the water. In-water cleaning of biofouling and dredging are likely expediting the spread of this invasive species unless biofouling can be contained and removed from the water.
KeywordsDidemnum vexillum Invasive species Tunicate
This research was funded by the NOAA Aquatic Invasive Species Program. We are especially grateful to K. Elaine Hoagland for her laboratory observations and insights into the reproductive biology and health indicators of living Didemnum vexillum colonies. We also thank A. Ostrowski for statistical support and J. Govoni, D. Ahrenholz, K. Elaine Hoagland, J. Dijkstra, and three anonymous reviewers for their helpful review of this manuscript. Mention of brand names or manufacturers does not imply endorsement by the U.S. Federal Government. The United States government has the right to retain a nonexclusive, royalty-free license on and to any copyright covering this paper.
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