The vessel as a vector - biofouling, ballast water and sediments

Human-mediated marine bioinvasions have altered the way we view the marine environment – virtually all regions of the global oceans have experienced the introduction of marine species (e.g., Carlton 1979; Coles et al. 1999; Cranfield et al. 1998; Cohen and Carlton 1998; Hewitt et al. 1999, 2004; Orensanz et al. 2002; Leppäkoski et al. 2002; Lewis et al. 2003; Castilla et al. 2005; Wolff 2005; Gollasch and Nehring 2006; Minchin 2006), placing marine and coastal resources under increased threat. Humans have almost certainly transported marine species since early attempts to voyage by sea. These ancient transport vectors were slow, and for the most part restricted to small spatial scales. The beginning of significant exploration and subsequent expansion by Europeans (post 1500 AD) has resulted in the transport of many thousands of species across all world oceans (Crosby 1986; diCastri 1989; Carlton 2001). The transport of species by human vectors was recognized by early workers (Ostenfeld 1908; Elton 1958), but it is only in the last few decades that significant progress on identifying patterns and processes has been made (e.g., Carlton 1985, 1996, 2001; Ruiz et al. 2000; Hewitt et al. 2004; Castilla et al. 2005; Minchin 2006). Numerous transport vectors have been identified and described (Carlton 2001; Chap. 5, Minchin et al.); however the majority of species appear to have been associated with vessel movements, either as exploratory, military, commercial or recreational vessels (e.g., Carlton 1985, 2001; Cohen and Carlton 1998; Hewitt et al. 1999; Gollasch et al. 2002, Minchin and Gollasch 2003). The ship as a transport vector is comprised of several sub-vectors. These include (1) the hull and other ‘niche’ areas, such as the propeller, rudder, on exposed surfaces of water piping, seachests, and thruster tunnels, where accumulations of growths of organisms develop (typically known as hull fouling), (2) the boring of organisms into the structure of the vessel (primarily limited to wooden hulled vessels), and (3) the uptake of organisms in association with wet or dry ballast (Carlton 1985, 1996; Ruiz et al. 2000). Several of these ship sub-vectors are no longer active. Hull boring for example, virtually ceased to exist with the use of steel G. Rilov, J.A. Crooks (eds.) Biological Invasions in Marine Ecosystems. 117 Ecological Studies 204, © Springer-Verlag Berlin Heidelberg 2009 118 C.L. Hewitt et al. as the primary ship-building material in merchant and naval vessels. However, many pleasure boats and fishing craft are still constructed of wood (Nagabhushanam and Sarojini 1997). Similarly, dry-ballast made up of sand, gravel and rock taken from littoral environments was replaced with water as ballast beginning in the late 1800s and had become phased out by 1950. None of these sub-vectors is species-specific, and each is likely to transport entire assemblages of species. Each may also facilitate the transport of a differing suite of species with different physiological and ecological characteristics (see Table 6.1). Biofouling primarily transports species that have attached sedentary or sessile, benthic habits, or species associated with these communities (e.g., living in, between or on other organisms) (Minchin and Gollasch 2003). In contrast, ballast water transports species associated with the plankton either as holo-plankton (species that have their whole life-cycle in the water column), mero-plankton (species with a portion of their life-cycle in the water column), or tycho-plankton (species accidentally swept into the water column), and often include pelagic species. It is difficult to establish a firm link between an already established introduced species and the vector (or sub-vector) by which it arrived in the new location (Minchin 2007). Nevertheless, attempts at assigning linkages to sub-vectors based on life history modes, timing of invasions, and association between location of incursion and subvectors have been deduced by reasoned argument (e.g., Hewitt et al. 1999, 2004, in press; Fofonoff et al. 2003; Ruiz et al. 2000)