Reducing propagule supply and coastal invasions via ships: effects of emerging strategies

Abstract

Ships' ballast water is a leading mechanism for the transport and introduction of nonindigenous species to ports worldwide. Two management strategies are being advanced to reduce propagule supply and invasions from overseas shipping. Ballast water exchange (BWE) is now required by several nations and is expected to be replaced by discharge standards (maximum organismal concentrations), negotiated as a treaty within the International Maritime Organization (IMO). Here, we provide the first forecast and comparison of changes to propagule supply at a national scale, resulting from these alternate management strategies. For unmanaged ballast water, sampled ships (n = 354) arriving to the US typically contained zooplankton concentrations < 3000 organisms m−3, but some ships (1.1%) contained > 50 000 organisms m−3. Only 3.8% of these arrivals meet the IMO standards. BWE substantially reduces zooplankton concentrations, but we estimate that ≤ 17.2% of BWE ships will meet IMO standards. Although most overseas arrivals discharged < 1500 m3 of ballast water, discharges are reported as high as 103 000 m3, and total inocula ≥ 106 remain possible, even under the more stringent IMO strategy.

Latitudinal Patterns of Biological Invasions in Marine Ecosystems: A Polar Perspective

“…While these sometimes focus on specifi c species that are known to survive or cause signifi cant impacts in a region, many strategies are now aimed at reducing transfers of all organisms associated with a known vector, especially because the number of potential species is vast and the risks of colonization and impacts are simply not known (i.e., have not been examined) for most species. As an example, this approach of vector management is now being applied to commercial ships in many countries, where ships are required to treat their ballast water before discharging in coastal areas, reducing the concentrations of all coastal organisms (e.g., Minton et al, 2005).…”

Interrupting a multi-species bioinvasion vector: The efficacy of in-water cleaning for removing biofouling on obsolete vessels

“…A recent and widespread vector management effort currently underway in marine systems is open-ocean ballast water exchange. By discharging coastal water (and associated organisms) from ballast tanks during ballast exchange and replacing it with oceanic water, the risk of species transfers from this vector can be reduced (e.g., IMO, 1991;Wonham et al, 2001;Minton et al, 2005;McCollin et al, 2007). Similarly, antifouling paints and hull husbandry reduce vessel biofouling transfers (Callow and Callow, 2002;Coutts and Taylor, 2004).…”

Marine invasive species in the Arctic

“…Propagule pressure has been shown to strongly influence the likelihood of invasion success (Lockwood et al 2005, Johnston et al 2009). Yet there remains significant uncertainty as to the exact relationship between propagule pressure and a quantifiable risk of invasion (Minton et al 2005, NRC 2011). Nevertheless, despite scientific uncertainty surrounding this relationship, there is broad agreement that reductions in propagule pressure should lead to significantly lowered risk of invasion , NRC 2011).…”