Introduction of Non-Indigenous Invertebrate Species in the Ballast Water of Ships

MB2080 Briefing Note

The introduction of non-indigenous invertebrate species in the ballast water of ships

PURPOSE

The purpose of this briefing note is to outline the potential risks of the introduction of Non-Indigenous Species (NIS) by ballast water and to present recommendations to decrease harmful effects of this event.

BACKGROUND

Historical records and studies indicate that fouling organisms first crossed oceans on man-made ships, where marine species encrusted onto wooden-hulled vessels were carried from port to port (Bax et al. 2003). As intra and inter-colony trade routes were established and immigration increased (Hewitt et al. 2004), maritime traffic across oceans led to an increased number of NIS in coastal water environments (Reise et al. 1998). In Australia, the history of marine biological invasions most likely began with European contact around the 1800s with exploration and colonisation (Hewitt et al. 2004). While wooden ships were still the main type of vessel used, crews would often scrub the hull and anchor chain at stops along the voyage (Bax et al. 2003). The shift from wooden-hulled to steel-hulled vessels in the modern era leading up to              World War 1 led to the shift from dry ballast to water ballast (Hewitt at al. 2004) as water ballast better controls trim, draft and stability, and helps to maintain safe and efficient transit conditions (Bailey 2015, Niimi 2004). The first signs of water ballast as a potential dispersal mechanism for holo, mero and tycho-plankton were recognised in the late 1890s (Bailey 2015, Hewitt et al. 2004). 

Becoming an invasive species is not easy, as many criteria must be met for that categorisation. A majority of potential invaders die as they cannot survive the dark and dirty conditions of ballast water tanks over long voyages. Further, invasive species that survive are likely to be confronted with unsuitable environmental conditions at the port of discharge, and even then, suitable species often fail to establish themselves. Most species that succeed in establishment fail to become invasive (Bax et al. 2003); however, the ones that do bring significant risk factors with them.

Newly introduced NIS can threaten biodiversity, marine industries and human health (Bax et al. 2003). Not only do NIS species alter the population of indigenous species by harming them directly, but they also alter the overall ecosystem. They also impact community and ecosystem processes and are therefore a significant force of change in global marine and estuarine communities (Ruiz et al. 2015). After identifying an increase in paralytic shellfish poisoning – whereby humans fall ill as a result of alkaloid toxin contaminated shellfish product consumption – Hallegraeff (1998) outlined a plausible scenario for the successful introduction and establishment of toxic dinoflagellate cysts in Australian waters. He stated that: 1) ballast water was taken in during seasonal planktonic blooms from Korean or Japanese ports, 2) survival of the resting cysts was high due to the voyage in dark ballast tanks, 3) after ballast water discharge, the germination of cysts was successful, accompanied with sustained growth and reproduction in Australian ports, and 4) coastal currents and domestic shipping led to further spreading and culminating under suitable environmental conditions in harmful algal blooms.

CURRENT STATUS

At any given moment, with transoceanic cargo shipping being truly global, ten thousand different species are being transported between bio-geographic regions in ballast tanks (Bax et al. 2003). The introduction of NIS into foreign habitats are therefore an inevitable consequence (Bastrop et al. 1998). While there is currently insufficient data to quantify the probability of invasion associated with any particular inoculum density (Bailey 2015, Ruiz et al. 2015), invertebrates appear to have higher breeding and establishment potential – which is increasing at a dramatic rate –because their diet and feeding behaviours suggest greater potential for extensive ecosystem alterations (Bax et al. 2003, Cohen et al. 1995).

The UN recognised that the transfer of invasive species across natural barriers is one of the greatest pressures to the world’s oceans and seas (David et al. 2019). The international convention for the control and management of ship’s ballast water and sediments (i.e. BMW convention) sets the global standards on ballast water management requirements with its aim to reduce the spread of potentially hazardous organisms among ports and other coastal areas (David et al. 2019).

RECOMMENDATION

For ballast water treatments to effectively reduce the density and richness of biota, and thus reduce the risk of transferring NIS (Bradie et al. 2010), ballast water management should satisfy each of the following criteria: 1) it must be effective at killing potential invaders, 2) it must be safe for the crew, 3) it must be environmentally friendly and 4) it must be affordable (Tamburri et al. 2002). Gollasch and Leppakoski (2007) proposed a management scenario that can achieve all of these. They suggest that the uptake of ballast water should be minimized or avoided in areas with outbreaks, infestations, sewage outfalls and phytoplanktonic blooms. Furthermore, ballast tanks should be cleaned on a timely basis in mid-ocean or, when the conditions are too rough to do so, under controlled arrangements in port or dry dock. Lastly, unnecessary discharge or uptake of ballast water should be avoided.

CONCLUSION
It is evident that NIS are a key contributor to environmental change that can result from various human activities, whereby the global movement of ballast water by ships appears to be the largest single vector. Invertebrate species have a proportionately higher chance of invading foreign ports and coasts due to their ability to survive and withstand considerably harsher conditions than other phyla. Centuries of global shipping trade without defined ballast management has now led to thousands of potentially hazardous NIS invasions – the most survivable being invertebrate species – which, if unaddressed, has the potential to cause significant and irreparable harm.

REFERENCES

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