Potential of the invasive colonial ascidian, Didemnum vexillum, to limit escape response of the sea scallop, Placopecten magellanicus

Jennifer Dijkstra,Riley Nolan

doi:10.3391/ai.2011.6.4.10

Abstract

Didemnum vexillum is a globally invasive species and a major pest to the aquaculture industry. Like other colonial ascidians, D. vexillum can readily overgrow aquaculture nets and cultured species. Recently, the species has been found in great abundance on seafloor habitats, where it is often associated with commercially important shellfish species such as sea scallops, Placopecten magellanicus. Despite the increasing abundance of D. vexillum in areas that are regularly fished for sea scallops, little work has been conducted on the ascidians impact on scallop behavior. This study examined the effect of overgrowth of the sea scallop by D. vexillum using four measures: time to initial exhaustion, swimming speed, horizontal and vertical displacement. Scallops covered by D. vexillum became exhausted more quickly, and were not able to swim as far in either the horizontal or vertical direction as the control sea scallops without D. vexillum encrustation. The expansion of D. vexillum into sea scallop habitat may increase the vulnerability of sea scallops to predation and limit their ability to access food rich habitats.

Highlights

The sea scallop, Placopecten magellanicus (Gmelin, 1791), is indigenous to the Northwest Atlantic, ranging from waters off Newfoundland and Labrador to Cape Hatteras, North Carolina at depths between 15 and 110 m (Posgay 1957)
While most nonnative species occur in shallow waters on artificial and rocky substrate (Ruiz et al 1997; Dijkstra et al 2007; Neves et al 2007), D. vexillum is often found in deeper waters in habitat preferred by sea scallops (Valentine et al 2007; Mercer et al 2009)
Sea scallops encrusted by Didemnum vexillum reached exhaustion more rapidly than unencrusted sea scallops (Figure 1)

Summary

Introduction

The sea scallop, Placopecten magellanicus (Gmelin, 1791), is indigenous to the Northwest Atlantic, ranging from waters off Newfoundland and Labrador to Cape Hatteras, North Carolina at depths between 15 and 110 m (Posgay 1957). This fishery represents one of the largest fishing industries in the United States with a catch of 24,000 tonnes that is valued at over $400 million US and is one of the most valuable wild scallop fisheries in the world (NMFS 2007). While most nonnative species occur in shallow waters on artificial and rocky substrate (Ruiz et al 1997; Dijkstra et al 2007; Neves et al 2007), D. vexillum is often found in deeper waters in habitat preferred by sea scallops (Valentine et al 2007; Mercer et al 2009)

Methods

Results

Conclusion