Wednesday, July 19, 2017

Look Out Captain - There are Aliens on the Hull!

Threat to Ecosystem Can Lurk Below the Waterline
Shipping News Feature
WORLDWIDE – These pages have often told in the past of the horrors which inadvertent biological pollution can cause when the ballast tanks of a vessel are emptied into a foreign environment without proper treatment. The fluctuating payloads on cargo ships, from container vessels to bulk carriers as they load and unload, make the use of such ballast essential and the threats have culminated in suitable regulations being introduced by the International Maritime Organization (IMO).

Now however comes a report from Tel Aviv University’s (TAU) School of Zoology which indicates that half the ships passing along the Mediterranean coast of Israel are carrying invasive ascidians on the outside skin of their hulls, presenting a global threat to ecosystems around the world. An examination of 45 dry-docked marine vessels, comprising recreational, commercial, and military craft, in five Israeli shipyards along the Mediterranean coast, revealed non-indigenous ascidians (NIA) on every second vessel investigated. Military vessels featured the highest ascidian abundance and richness, potentially related to their maintenance routine. TAU’s Dr Noa Shenkar, who led the research, said:

“These organisms are passing through the Suez Canal, latching onto ropes and the bottom of the ship. They're filter feeders, so they cover and clog every surface they latch onto, creating a lot of drag for the ship and damaging marine biodiversity in their new environments. They're a major threat to our coasts and are very costly to ship owners."

Among the wide occurrence of non-indigenous ascidians, TAU researchers also discovered a Caribbean species new to the region. The findings, state the authors of the report, ‘strongly support the hypothesis that marine vessels constitute a substantial vector for the introduction and dispersal of NIAs’.

The research also finds ‘the method of rapid high-pressure fresh-water wash fails to provide adequate treatment for removal of invertebrates inhabiting internal hidden areas; especially ascidians, that can survive the dry-docked time outside the water. Of greater concern is that it allows vessels to continue their regular operations and at maximal speed for longer periods; conducting a thorough maintenance procedure every 3–4 years rather than every 1–2 years’.

The use of organotin compounds acting as biocide in anti-fouling paint, particularly Tributyltin (TBT) was completely banned in 2008 by the IMO’s International Convention on the Control of Harmful Anti-fouling Systems on Ships after evidence emerged that these, whilst poisoning potentially hazardous passengers on the hull, it also slowly leaches out into the marine environment where it is highly toxic toward non-target organisms.

TBT can bond to suspended aquatic material and its toxicity released up to thirty years later and, by poisoning lower life forms such as algae, can in turn cause harm through molluscs right up the food chain even affecting humans. One of the effects observed in molluscs is to turn the male hormone androgen into its female equivalent oestrogen, drastically affecting reproduction levels.

The new report has naturally been seized upon by those with a vested interest in the mechanical cleaning of vessel hulls. Ensuring a smooth surface under the water can have beneficial effects in terms of performance but obviously involves regular maintenance costs, whether by traditional methods of dry docking and high pressure hose washing or the latest remote underwater robot technology. Belgium headquartered Subsea Industries, which manufactures the Ecospeed hull coating system, welcomed the report with chairman Boud Van Rompay saying:

“This research substantiates what we said in January this year; that the entry into force of the Ballast Water Convention will not alone prevent the transfer of invasive aquatic species. There has to be mandatory legislation in place to prevent biofouling on ships’ hulls. Hopefully this research will generate greater awareness of the problem and result in appropriate action.

“The NIA threat is increasing because the antifouling systems in use since the TBT ban have been less effective in eliminating hull fouling. There is currently no miracle cure that will, on its own, prevent the spread of NIAs. The only known way of removing the threat is to clean the fouling organisms off mechanically, which is only possible with a hard-type coating. This ensures the underlying protective coating is not damaged. The industry has to consider taking a different approach to hull protection.”

Photo: The New Zealand mud snail which can survive for up to 50 days on a damp surface and has effectively spread from its home country to many areas from Iraq to the US where the lack of natural predators has resulted in concentrations greater than 500,000 per m2, endangering the food chain by outcompeting native snails and water insects for food, leading to sharp declines in native populations.