"We are on the verge of the sixth extinction" Stuart Pimm, Professor of Conservation Ecology at Duke University concludes.  Earlier this year a study, of which Pimm was lead author, calculated current human-induced rates of extinction to be 1000 times greater than the background.  The human-induced causes for extinction are myriad but can be broadly categorised as habitat loss, over-exploitation, pollution, climate change, and non-native invasive species.  Non-native species are any species that has been brought to an area outside its natural past or present day distribution by human activity.  When a non-native spreads altering the environment to which it has been introduced, and/or impacting on human health or the economy, the species is classed as invasive. 

Some invasive species are those species deliberately introduced, like the cane toad in Australia which was deliberately released in Queensland in 1935 to control sugar cane pests.  Most invasives however, are introduced accidentally.  The pathways for accidental invasion are inextricably tied with human movement. 

Be it the actual organism itself, seeds, eggs, or gametes, “the spread of problematic non-native species” Dr Mark Spencer, senior curator of the British and Irish herbarium at the Natural History Museum London told the UK Parliamentary Environmental Audit Committee just this year, “has been closely correlated with the development of international trade over the last 150 years”.  With over 90% of international trade involving ocean travel, sea freight is a major invasive pathway, and the prime culprit is ballast water. Ballast water, which is essential to maintain the effective and safe running of freight vessels when they are not fully loaded, is typically taken from sea water at or near one port, and discharged at another. Alongside the sea water itself, marine organisms – small animals and larvae, viruses, bacteria, and algae are also taken in – and discharged.  As shipping has increased and extended across the globe, so too has the amount of ballast water.  Today an estimated 3.1 billion tonnes of ballast water is discharged annually.  

Not all organisms taken on in ballast water will become invasive.  Depending on the time between taking in ballast water and discharging it again, organisms may simply die in transit, either due to short life spans or simply lack of sufficient resources needed to stay alive.  Those which survive may not necessarily become invasive, with unfavourable environmental conditions at the discharge point hampering population growth.  Never-the-less the marine invasive problem has fast become a global issue.  A 2008 study lead by Jennifer Molnar, director of science for The Nature Conservancy found that invasions had been reported in 84% of the 232 World’s marine ecoregions.

When a marine species does become invasive, the impacts can be devastating.  The Chinese mitten crab (Eriocheir sinensis), a native of Korea and China was first reported in Europe in 1912 in Germany, but has rapidly spread.  Their penchant of burrowing has altered habitats and eroded estuarine and river banks, with an estimated economic cost to Germany alone at €80 million.   Alexandrium minutum, the dinoflagellate famed for causing it’s toxic ‘red-tide’ has spread from its native European waters to the South China Sea, New Zealand, south-east Australia, and New York.  With blooms of the dinoflagellate presenting a high risk of causing paralytic shellfish poisoning (PSP), red-tides effectively halt fishing and aquaculture in their vicinity, as well as presenting toxic impacts on fish and invertebrates.  In the Gulf of Mexico the Australian spotted jellyfish (Phyllorhiza punctata) has become both an ecological and an economic threat to the region due to its propensity to consume vast quantities of eggs and larvae - including those of commercially important species. 

Once established, it is virtually impossible to eradicate marine invasives from an area.  This is not simply a case of ‘prevention is better than cure’, more that cure is unlikely to even be an option.  Prevention, the United Nations and IMO hope, could lie in the 2004 International Convention for the Control and Management of Ships' Ballast Water and Sediments.

The Convention charges signatories with a somewhat complex task: “prevent, minimize and ultimately eliminate the transfer of harmful aquatic organisms and pathogens through the control and management of ships’ ballast water and sediment”.  From the perspective of reducing the likelihood of a marine invasive being introduced, the Convention has two key requirements –effective ballast water inspections that can accurately identify vessels which fail to meet Convention requirements, and effective ballast water treatment systems that ensures that organism concentrations in the ballast water are below specified limits before discharge takes place.  Ballast water sampling can either be done on the vessel itself, or at a land-based/barge based lab, but the process is not as straight forward as one may hope. 

For starters tank sampling points vary depending on the ships age, dimension, type, and operation, meaning that there is not one sampling technique that is suitable for all.  Then there is the organisms themselves which, as Dr Katherine Carney demonstrated in an experiment for her thesis, are not necessarily evenly distributed throughout the ballast tank.  Katherine sampled discharge for known levels of Tetraselmis suecica, marine algae.  63% of the samples either overestimated or underestimated actual densities.  Furthermore, there is no single sampling technique that can adequately capture all organisms.  Sampling, as highlighted in a 2007 study lead by Dr Stephan Gollasch, an independent consultant and advisor to the IMO, can also be a time consuming process, with an estimated average of 50 days needed for land-based tests, and some 6 months for ship based tests.  Both options are costly, both in terms of equipment, financial requirements and man-power.  It is unclear how ready signatories are to implement the required testing.

Treatment largely falls under the remit of shippers.  Over 20 commercial treatment systems have so far been certified as compliant to the Convention by the IMO.  These measures, Barbara Werschkun of the Federal Institute for Risk Assessment in Germany reports in a study she lead earlier this year, can be broadly divided into chemical processes, such as using chlorine to effectively ‘disinfect’ the water, and mechanical-physical processes such as filtration systems that separate larger organisms from the ballast water alongside UV treatment that kills them off.  No treatment can kill 100% of organisms, though some may also confer benefits to shippers.  A study lead by Dr Mario Tamburri, marine ecologist for the Monterey Bay Aquarium Research Institute and Monterey Bay National Marine Sanctuary in 2001 suggested that deoxygenating ballast water with nitrogen had the potential to not only induce significant mortality of ballast water organisms (with exception of those with life stages resistant to hypoxia), but also reduce ballast water tank corrosion.

Once a vessel wants to discharge ballast water, they must do so in a ‘safe’ area.  The Convention calls for exchange to take place ideally 200 nautical miles from the nearest land, in waters no less than 200 metres in depth.  If this is not possible, 50 nautical miles from the nearest land, and in waters of at least 200 metres in depth is acceptable.  Failing the availability of these options, ballast water exchange areas, where the environmental impact of exchange is minimised, can be designated.  Identifying such areas presents a challenge in itself.  The area needs to be as far from land as possible, and as in deep water as possible.  It also needs to be large enough to cope with the shipping traffic, and close enough to shipping routes so not to unduly hamper shipping operations whilst not impacting on other ocean users such as fishers, or in conservation zones. 

This situation becomes even more complex with the need to take into account oceanographic conditions, which in some areas may be poorly understood.  Diffusion and dispersal of ballast water is better in areas where there are strong currents moving offshore, but also needs to take into account any spatial and temporal variability in current movement as well as localised oceanographic variables which can also alter the suitability of sites over short time scales.  Effective diffusion isn’t just important for reducing the risk of invasion, but for minimising the impact of chemical biocides used in some treatment systems.  The introduction of TBT (Tributyltin) as an antifouling biocide in the 1960s caused widespread ecological damage as well as impacting of aquaculture and fisheries. 

The hazard that the substance presented and its propensity to accumulate and persist in the environment, was severely underestimated.  To this day, historic TBT contamination remains a problem in several areas.  Identification of suitable areas is absolutely critical.  Get it wrong and you could end up with exchange areas, or indeed areas down current, in which invasives establish through repeated exchange, or are contaminated with detrimental effects to the localised environment.  One suggested alternative is to store chemically treated ballast waters (alongside those that do not meet Convention requirements for open-ocean exchange) in land-based tanks.  The lack of suitable infrastructure at many of the World’s ports and ships required does not, as yet, make this a viable option in many regions.

For the Convention to make an impact on marine invasives and to be practically applicable, a global standard for ballast water treatment and vessels inspection/testing is required.  As at October 2014 just 43 states/parties had ratified the Convention, representing 32.54% of the global merchant fleet tonnage.  For the Convention into force, at least 30 states representing at minimum 35% of the global merchant fleet tonnage needs to ratify it.  Even when the 35% target is met, this means that 65% of the global tonnage will not necessarily conform to Convention standards. 

The lack of globally consistent guidelines presents a challenge for shippers in respect to ensuring compliance, but it also presents a challenge for reducing the impact of marine invasives.  Furthermore it is not unreasonable to hypothesise that an invasion from non-signatory bordering nation is possible.  As Dr Richard Shaw, Regional Coordinator for Invasives in Europe and the Americas at CABI, noted at the UK Parliamentary Environmental Audit Committee, it just "takes one rogue trader, an internet order or contaminant to start a new invasion".  Since the adoption of the Convention in 2004, new marine invasions are still being reported globally, even in the waters of signatories.  For example, the North-American comb jelly (Mnemiopsis leidyi) which upon release into the Black Sea in the 1980s grew to such an extent that its biomass reached 10 times the world’s annual fish landing, decimating fish stocks has been reported in Germany, Sweden, and the Kiel Bight from 2004 onwards. 

What is clear is that tackling the marine invasive problem is going to be difficult task, requiring a global effort.  What is less clear is if the Convention will succeed in making a meaningful contribution to the task.  However if the Convention is not ratified, and nation states do nothing then we will have failed without even trying.

This story was written for The Marine Professional, a publication of the Institute of Marine Engineering, Science & Technology (IMarEST).