Supply-side invasion ecology: characterizing propagule pressure in coastal ecosystems

Abstract

The observed rates and deleterious impacts of biological invasions have caused significant alarm in recent years, driving efforts to reduce the risk (establishment) of new introductions. Characterizing the supply of propagules is key to understanding invasion risk and developing effective management strategies. In coastal ecosystems, ships' ballast water is an important transfer mechanism (vector) for marine and freshwater species. Commercial ships exhibit a high degree of variation in ballast water operations that affect both the quantity and quality of propagule supply, and thereby invasion risk. The per-ship inoculation size from ballast water depends upon both the volume discharged and the organism density. Moreover, propagule quality will vary among source regions (ports) and voyage routes, due to differences in species composition and transport conditions, respectively. We show that significant differences exist in (i) the frequency and volume of ballast water discharge among vessel types, (ii) the frequency of vessel types and routes (source regions) among recipient ports, and (iii) the transit success (survivorship) of zooplankton in ballast tanks among voyage routes. Thus, propagule supply is not a simple function of total ship arrivals. For ships, as well as other vectors, variation in propagule quantity and quality must be explicitly considered to estimate invasion risk and advance predictive ability.

Predation contributes to invasion resistance of benthic communities against the non-indigenous tunicate Ciona intestinalis

“…Invasibility is mediated in terms of variation in the timing and intensity of propagule supply. Human-mediated propagule introductions are usually singular events (e.g., ballast water) that can sometimes occur repeatedly (Carlton and Geller 1993;Verling et al 2005) but this sporadic propagule supply is often too small to permit introduced species to invade natural habitats due to the strong predation pressure in natural communities (Drake and Lodge 2006), i.e., the Risky Roulette scenario (Fig. 3).…”

Intra-coastal ballast water flux and the potential for secondary spread of non-native species on the US West Coast

“…In addition, variability among vessel types, source regions, voyage season, routes and durations can alter the types, numbers and viability of organisms being transported (i.e. propagule supply; Verling et al, 2005). Once a nonnative population is successfully established within a port, the system itself may become a source for subsequent introductions through passive range expansion or secondary spread through further human transfer (Wasson et al, 2001;Ruiz et al, 2006).…”

“…Intra-coastal ballast water transport can increase the spread of ANS by expanding the range of established invaders through secondary spread (Lavoie et al, 1999;Mines et al, 2004;Niimi, 2004). Coastal voyages are favorable for the spread of ANS because ballast organism survivorship is higher for shorter voyage durations (Carlton, 1996b;Lavoie et al, 1999;Verling et al, 2005). To address the federal loophole on the US West Coast, state regulations were adopted in 2002 in Washington and Oregon, and 2006 in California, which require most vessels traveling coastally to exchange their ballast 50 nm from shore (exemptions remain for certain voyage routes).…”

Early phase of the invasion of Balanus glandula along the coast of Eastern Hokkaido: changes in abundance, distribution, and recruitment

“…Propagule pressure often plays an important role in determining whether the introduced species is able to successfully establish itself and extend its distribution (Lockwood et al 2005;Drake and Lodge 2006;Roman and Darling 2007;Johnston et al 2009;Simberloff 2009). Although many previous studies have focused on the early phase of invasion dynamics (Strayer et al 1996;Carey 1996;Crooks 2005Crooks , 2011Gaubert et al 2009), most of these studies have not included an estimate of propagule supply (Cohen and Carlton 1998;Costello and Solow 2003;Marchetti et al 2004;Jeschke and Strayer 2005;Brown et al 2008;Miller and Ruiz 2009;Marsico et al 2010), especially in marine habitats (but see Ruiz et al 2000;Verling et al 2005;Clark and Johnston 2009;VazPinto et al 2012).…”