Non-native Marine Invasive Species (Guy Baker)

Saturday, 26th February 2011

“You should clean your bottom every year”! Australians and New Zealanders are known for plain speaking, but this seemed unnecessarily rude. However, just to clarify, they were talking in this instance about the hull of your boat.  The point was quickly driven home by an underwater film, taken in N.France, which showed a hull so thickly coated with weeds and invertebrates that it looked like a sagging roll of shaggy carpet.  Boat fouling is a worldwide problem and marinas and harbours are important staging posts in the process, because hulls, piers and jetties provide numerous firm surfaces on which sessile plants and animals can gain a foothold.  It only takes a few weeks for a surface to be completely colonised.  Increasingly, however, it has been found that the plants and animals are not simply extensions of the local ecosystem, they include alien species which have invaded from different parts of the world.  Recognising that this was a problem, the Marine Biological Association (MBA) in Plymouth entered a consortium with the Scottish Association for Marine Science, the Natural History Museum and other research institutions to research the issue of Marine Aliens.

Guy Baker, the MBA’s Communications and Outreach Officer, gave us a comprehensive review of the subject.  What are marine invasives?  Why and how have they come here and where are they now?  One definition of invasive non-native species (sometimes shortened to INNS) is that they are plants or animals, introduced by humans, which have the ability to cause damage to the environment, the economy or our way of life or health.  A difficulty emerges with the term ‘non-native’.  The reference level is taken to be the 19th Century, when marine biology and taxonomy became established as sciences, but there is historical evidence that plants and animals were introduced by the Romans throughout Europe and progressively from the 1300s as world exploration took place.  Some of our familiar ‘native’ species must be classified as cryptogenic, of unknown origin.  Size is another factor.  Alien molluscs and crustacea, such as the Chinese mitten crab, are conspicuous invasives, but smaller forms are less obvious.  The European prawn had become well established in Chesapeake Bay before it was detected.  A graph showing exponential increase of macroalgae in the Mediterranean since 1900 prompted thoughts on possible causes:  multiple invasions?, global warming?, more recording?, changed human activity?

There are many reasons to be concerned about marine invasives.  While some forms can be welcomed, having arrived in small numbers and settled with native species, contributing to biodiversity, others have had dramatic impact, economic and social, upsetting the balance of the ecosystem.  They can be responsible for fouling marine vessels, installations and aquaculture, competition with native species, alteration of the substrate and water; and smothering of, or predation on, native species.  Many are resilient, fast-reproducing and unhindered, with no local predators.  They have arrived attached to the hulls of commercial or recreational vessels, or carried in ballast water, or as contaminants of shellfish or via seafood trade.  Figures indicate that global maritime transport accounts for 60% of the movement of invasives.  Particularly telling were data showing that invasives reaching Melbourne had come dominantly from the NE Atlantic, with lesser numbers from the Mediterranean and Pacific, a clear correlation with trade routes.

Information is vital in drawing up a strategy to deal with the invasive threat.  The GBNNSIP (Great Britain Non-Native Species Information Portal) has established an alerts system, whereby new arrivals in UK waters are reported to the Biological Records Centre, verified by experts and then notified to relevant authorities via websites such as MarLIN (Marine Life Information Network) and GBNNSIP.  The biological characteristics are important.  How does the species reproduce?, what are its migration patterns?  For example, sea squirt larvae do not feed and are relatively short lived and so the distance the organism can spread by larval means is limited.  Other species’ larvae can remain dormant for a long time in ballast water.  The Chinese mitten crab lives much of its life in fresh water and has now colonised northern rivers and the Thames as far as Didcot.  Preventing the spread of a species, if possible, is a better option than dealing with its presence and this may involve changes to working practices.  Moving a pontoon to another area, for instance, carries the risk of spreading an alien species.  New developments such as marinas and wind farms should ensure that biosecurity is built in at the planning stage, while existing developments should follow codes of practice, such as the Green Blue scheme backed by the Royal Yachting Association.  Clearly hull scrapings should be put in a skip, not dumped back in the sea, but what should be done with the wash water?  As pointed out by the RYA, small pieces of weed adhering to boat trailers or microscopic larvae or eggs surviving in damp ropes can transfer species from one body of water to another.

Leisure craft are the main vectors of secondary dispersal in UK waters.  A survey of boats in the 30-40 ft range in a Plymouth marina showed that over 80% of hulls carried the Pacific bryozoan Tricellariainopinata and Darwin’s barnacle Elminius modestus, while sites infected by the carpet sea squirt Didemnum vexillum are marinas on leisure craft routes, not ferry terminals.  Didemnum, an invasive colonial filter-feeder originally from Japan, forms sheets and rope-like masses which can smother mussel farms and so Holyhead marina began an eradication programme in late 2009, progressively wrapping the pontoons and mooring chains with plastic sheets and bags with calcium hypochlorite to cause death under anoxic conditions.  The first year of the programme has cost £200,000 and been largely successful, although reinfection did occur in places during the eradication attempt as larvae from untreated areas reached cleaned pontoons.  Unfortunately funding has now been withdrawn.

The Marine Aliens consortium focussed on monitoring dispersal pathways, classifying marinas and harbours for hull fouling potential and assessing the likely impact of control systems on native biodiversity.  A meeting was held in February at the Linnaean Society in London to mark the end of the present run of the project and review the findings of the consortium’s research.  Many of the presentations can be viewed on the Marlin

Among other invasives present in South-West waters are the slipper limpet, Crepidula fornicata, which was introduced from the eastern USA in the 19th Century and is particularly successful at competing for food and territory with local oysters, and the leathery sea squirt, Styelaclava, a Far-Eastern species which arrived in Plymouth in 1953, possibly on boats returning from the Korean War.  It fouls mussel ropes, submerged gear and oyster beds.  The wireweed, Sargassum muticum, is a brown alga which is a vigorous coloniser of rock pools.  Wakame, Undaria pinnatifida, is another brown alga which was imported from the Far East to France as a food crop but subsequently escaped.  Another possible arrival is the veined rapa whelk, Rapana venosa, a competitor of the native whelk and predator of bivalves, which was confirmed in the North Sea in 2005.  The list goes on; and is increasing each year—— which underlines the need for a clean bottom!

The HMCG wishes to express sincere thanks to Guy Baker for his very detailed and informative talk and for suggestions which have been incorporated in this report.

© Helford Voluntary Marine Conservation Area