Fragment reattachment, reproductive status, and health indicators of the invasive colonial tunicate Didemnum vexillum with implications for dispersal

This manuscript is not subject to U.S. copyright. The definitive version was published in Biological Invasions 14 (2012): 2133-2140, doi:10.1007/s10530-012-0219-8.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 three 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.This research was funded by the NOAA Aquatic Invasive Species Program

Effects of chronic bottom fishing on the benthic epifauna and diets of demersal fishes on northern Georges Bank

Feeding by demersal fishes on benthic invertebrates constitutes an important link between fishery resources and continental shelf habitats. However, concurrent sampling of demersal fish diets and benthic invertebrate prey fields has been limited, particularly in relation to chronic bottom fishing disturbance on continental shelves worldwide. Here, we quantified differences in the epibenthic invertebrate and fish communities between sites with contrasting levels of disturbance from mobile bottom fishing gear for 2 gravel regions of Georges Bank in the northwest Atlantic. The main objectives were to compare a suite of biological indices for epibenthic invertebrates, demersal fishes, and fish diets across year and level of fishing disturbance. The fishes selected for diet comparisons included winter skate Leucoraja ocellata, little skate L. erinacea, Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, winter flounder Pseudopleuronectes americanus, and longhorn sculpin Myoxocephalus octodecemspinosus. Three baseline benthic epifaunal indices, species richness, abundance (no. l-1), and biomass (g l -1), were lower in the heavily fished areas; however, evenness was higher in these areas. The lengths of haddock, Atlantic cod, and winter flounder tended to be larger at the undisturbed sites. Fish stomach contents differed significantly among habitats for 3 benthivores: haddock, winter flounder, and longhorn sculpin; diets were more highly correlated with the benthic fauna within than among sites, which indicated site-specific feeding. In several cases, prey that contributed to the diet dissimilarity between sites were benthic epifauna most sensitive to the impact of bottom fishing disturbance; thus, the availability of epibenthic prey was determined by this disturbance. © Inter-Research 2013