Why are invasive species problematic?

As unavoidable as it might sound for any successful species to expand its geography, today’s world is one in which a species can end up transported 10s of 1000s of km away from its native range, which can quickly create an unnatural imbalance, and which is why compliance is now mandatory. Invasive species are problematic for various reasons:

• Factors (ie predators) that limit the invasive species where it came from are either absent in the new area, or
• Invasive species outcompete native species for resources and quickly become dominant, or
• Invasive species act as a vector for viruses and diseases that the native species do not have resistance for.

The latter has been a particular concern in the horticultural world, with such things as Xylella (a plant pathogen) ravaging Europe, and Ash Dieback, another plant pathogen, responsible for up to 99% of Ash deforestation in the UK. It should however also be noted that whilst the arrival alone of invasive species in a habitat does not always guarantee a threat – some species establish in a new habitat with few disruptions – the majority of invasive species do alter ecosystems or increase the extinction risk for native species.

“An example of a problematic invasive species is the Pacific Oyster.  Growing faster than native oysters, Pacific oysters form large clumps along intertidal shorelines and bays”

An example of a problematic invasive species is the Pacific Oyster.  Growing faster than native oysters, Pacific oysters form large clumps along intertidal shorelines and bays.  Farmed correctly, Pacific oysters can represent a financial benefit, but escaping into wider non-farmed areas and left to their own devices, they outcompete native species and damage ecosystems.  As filter feeders, they consume large amounts of food, reducing availability for other species, causing a reduction of fish harbours, as fish go elsewhere to eat.  The oysters are not necessarily always a good source of food, as contaminants in the waters, which oysters filter, can build up in the flesh, creating high toxin levels.

“This problem is very much a man-made problem, as international trade is now responsible for the majority of invasive species”

This problem is very much a man-made problem, as international trade is now responsible for the majority of invasive species. There are various ways through which international trade is responsible for this problem, although this hasn’t always been the case. Historically, as geography succumbed to the travel means that opened up the world, so-called Victorian ‘acclimatisation’ societies imported species from one locale to another, be it for ornamental interest, such as the case of Ponticum (rhododendrons) in the UK, or as a hunting resource (such as rabbits in Australia), or as a food crop (such as the Pacific Oyster, globally). By the early 20th century however, acclimatisation societies became a thing of a bygone era, and international trade became the dominant vector for invasive species. For most of the 20th century, globalisation moved goods from one location to another with little or no inspection or regard for the species that come along with such goods.

Ballast water and invasive species

The use of ballast water in shipping is a standard mechanism that has been used since the dawn of the age of sail. As a vessel receives or delivers cargo to a number of different ports, it will take or release ballast water at each one. Almost all sea-going vessels use ballast water for sea-faring reasons – freshwater or ocean water stored in a ship’s hull to add weight which gives a vessel a more optimal line in the water, providing stability and improving maneuverability during a voyage. Once a vessel reaches its destination, ballast water is then discharged at the new port whilst it unloads, and new ballast water taken on for the next voyage.

Humanity’s reliance on maritime trade rapidly affected the way marine organisms are transported within the ocean.  Molnar et al. 2008 documented the pathways of hundreds of marine invasive species and found that shipping was the dominant mechanism for the transfer of invasive species. Shipping transfers invasive species around the globe in two ways: hull fouling and ballast water transport. Many marine organisms have the capacity to attach themselves to vessel hulls. Therefore, such organisms are easily transported from one body of water to another and are a significant risk factor for a biological invasion event. Controls for vessel hull fouling are largely voluntary and there are currently few regulations currently in place to manage hull fouling. However, the governments of California and New Zealand have announced more stringent control for vessel hull fouling within their respective jurisdictions, and recently there have been cases of passenger vessels refused permission to dock because of hull fouling.

The other main vector for the transport of non-native aquatic species is ballast water. Ballast water taken up at sea and released in port by transoceanic vessels is in fact the largest vector for non-native aquatic species invasions and it is estimated that 10,000 different species, many of which are non-indigenous, are transported via ballast water each day. Many of these species are considered harmful and can negatively affect their new environment. For example, freshwater zebra mussels, native to the Black, Caspian and Azov seas, are believed to have reached the Great Lakes via ballast water from a transoceanic vessel. 

“Ballast water taken up at sea and released in port by transoceanic vessels is the largest vector for non-native aquatic species invasions and in fact, it is estimated that 10,000 different species, many of which are non-indigenous, are transported via ballast water each day”

For organisms between 10 and 50 microns, such as certain types of phytoplankton, current regulations do allow less than 10 cells per milliliter be present in discharge from treatment systems. Whilst this helps against invasive species, it should be noted that many species of phytoplankton are less than 10 microns in size and reproduce asexually. Only one cell released into the environment can grow exponentially into many thousands of cells over a short amount of time; for example, some species in the genus Pseudo-nitzschia are smaller than 10 microns in width and contain domoic acid, a neurotoxin. If toxic Pseudo-nitzschia spp. are alive in ballast discharge and are released into a new environment, they could cause domoic acid poisoning in shellfish, marine mammals and birds. Human deaths following such an incident occurred in a domoic acid outbreak in Canada in 1987, and it would not be surprising if ballast water regulations regarding the allowance for smaller organisms between 10 and 50 microns becomes more rigorous over time to prevent future ramifications associated with the potential release of toxic and invasive phytoplankton.

Ballast water compliance regulations

The International Convention for the Control and Management of Ships’ Ballast Water and Sediments (BWM Convention) was adopted by consensus at a Diplomatic Conference held at IMO Headquarters in London on 13 February 2004 and entered into force globally on 8 September 2017. The Convention requires all ships to implement a ballast water management plan for compliance – all ships are required to carry a ballast water record book and are required to carry out ballast water management procedures to a given standard. Parties to the Convention are given the option to take additional measures which are subject to criteria set out in the Convention and to IMO guidelines. The Guidelines, some of which have been revised since their initial adoption, and a number of other relevant guidance documents can be accessed here, but in summary:

• The D-1 compliance standard requires ships to exchange their ballast water in open seas, away from coastal areas. Ideally, this means at least 200 nautical miles from land and in water at least 200 metres deep. By doing this, fewer organisms will survive and so ships will be less likely to introduce potentially harmful species when they release the ballast water.
• The D-2 compliance standard specifies the maximum amount of viable organisms allowed to be discharged, including specified indicator microbes harmful to human health. The D-2 standard specifies that ships can only discharge ballast water that meets the following criteria:
  • Less than 10 viable organisms per cubic metre which are greater than or equal to 50 microns in minimum dimension;
  • Less than 10 viable organisms per millilitre which are between 10 microns and 50 microns in minimum dimension;
  • Less than 1 colony-forming unit (cfu) per 100 mililitres of Toxicogenic Vibrio cholerae;
  • Less than 250 cfu per 100 millilitres of Escherichia coli; and
  • Less than 100 cfu per 100 milliliters of Intestinal Enterococci

FastBallast

• Chelsea’s FastBallast is a portable instrument that provides rapid on-board testing of treated ballast water to ensure compliance with the IMO D-2 & USCG Discharge Standards around invasive species
• Quick & cost-effective – compliance level test in under 10 minutes decreasing need for shore-based laboratory involvement
• Accurate – the most accurate indicative compliance instrument on the market, removing the cost to go back out to sea, exchange ballast water and return to port
• Simple – all-in-one portable instrument, including tablet, no consumables, designed to be operated by a single person
• Future-centric innovative STAF technology also provides detection of living cells and cell density, beyond the current requirements of compliance testing