A Global Overview of Ascidian Introductions and Their Possible Impact on the Endemic Fauna

Abstract

Recent surveys of invertebrates in many coastal areas throughout the world demonstrate the ever-increasing rate of introduction of nonindigenous ascidians. Harbors, with their pro tec ted waters and large marinas, are usually the entry points for organisms carried in ballast water or on boat hulls. Marina floats, harbor buoys and boat hulls provide a huge surface area for settlement. Introductions may be further aided by transport of contaminated shells or live bivalves between mariculture facilities. Many ascidians reach sexual maturity and produce a second generation in just a few weeks. This review summarizes the results of recent studies of coastal areas, ballast water and harbor structures in many parts of the world, and sampling of V.S. Navy drydocks recently moved between major Pacific ports. Some of these studies include companion surveys of neighboring natural shallow environments. Most natural areas appear to have resisted invasions of nonindigenous ascidians except where perturbation has resulted in a decrease in species diversity.