FOULERS AND FISHERIES
Pradeep KumarP. Gangeswari andM. Venkatasamy
Fisheries College and Research InstituteTamil Nadu Veterinary and Animal Sciences University
Thoothukudi-628 008
A silent battle has been in vogue since time immemorial between man and marine
foulers. It began the day when man launched his first fishing boat in the sea which was
then translated into beautiful ship designed to give maximum speed and fuel efficiency.
But the efforts are in vain, as the most simple and harmless looking marine foulers attach
to the underside of the ship within hours of its launching and exert damage. Human
beings came up with a variety of protective measures, many of them ingenious but
virtually none are fool proof. This ceaseless war between man and marine foulers
spanning several centuries is yet to prove its might.
PROCESS
Marine fouling is a common but complex succession of processes which involves
settling, interaction and subsequent accumulation of organic materials, both living and
non living on a submerged solid surface. Fouling organism refers to any marine life
living in an area that interferes with human activities. Fouling process usually begins with
the formation of a slime film. It starts minutes after initial submergence of vessel with the
adsorption of a thin layer of organic material over the exposed surface. This layer
provides a base for the adherence and growth of pioneer bacteria which begin to colonize
the surface within a few hours of submergence. Days after this, microscopic organisms
such as diatoms and protozoans begin to adhere and grow upon the submerged substrata.
These organisms combined with already existing colonies form a complex slimy layer.
This soon becomes an ideal home for the attachment of large marine foulers including
barnacles, sea squirts, algae and worms. Biofouling, thus, is divided into microfouling
(slime formation and bacterial adhesion) and macrofouling (attachment of larger
organisms).
IMPACT
Foulers attach in large numbers and seriously slow down the speed of the fishing
vessel, thereby increasing the fuel consumption. Though trawlers in India maintain an
average speed of 7 to 11 knots under normal fishing cruise, about 38 to 50% loss of speed
was reported under heavy fouling conditions. Another problem in the warm tropical
waters is the intensive settlement of the fouling organisms on the boat hulls of fishing
vessels. Foulers are often transported great distances on the bottoms of ships or other
floating wood to which they are attached. An average accumulation of fouling forms
weighing 10-15 kg/m2 of hull surface exposed to sea water has been observed during a
period of 7-8 months of active service. Indian fishing fleet is fast expanding both in size
as well as in numbers. The entire economy and the well being of the Indian fishing
industry depend on the efficient operation and management of the fishing fleet. Likewise,
marine fouling is of particular concern on the components mounted on the hull of the
submarine ships such as sonar dome with rubber windows and other protective
enclosures. Foulers also pose serious threat the cages employed in aquaculture and other
structures exposed to sea water. World wide the cost of keeping at bay these unwanted
marine organisms comes approximately to about US $ 4 billion a year.
CONTROL
Woods Hole Oceanographic Institution (WHOI) which was funded by the
US Navy during World War II to develop effective controls to marine fouling estimated
that up to 1/3 of the fuel used by war ships could be saved if fouling was eliminated.
WHOI pioneered the use of compounds containing heavy metal bottom paints (lead,
copper etc.). These antifouling paints of chemical preparations worked very well acting
as general biocides. Currently, marine fouling is controlled mainly by a heavy metal
compound, Tributyl tin oxide (TBT/TBTO). This organotin paint gives protection up to
five years. Later research has shown these heavy metal compounds to be hazardous to all
life in the sea, especially in shallow bays and harbors. The downside to TBT started to
emerge when it became clear that the organisms that foul the hulls were not the only the
exclusive victims. It was also observed that TBT causes other ill effects including sex
reversal in marine gastropods. Extremely low concentrations of tributyltin was found to
cause defective shell growth in the oyster, Crassostrea gigas (at a concentration of
20 ng/l) and development of male characteristics in female genitalia in the dog whelk,
Nucella lapillus. TBT is also known to be harmful to a wide range of other aquatic
marine organisms including microalgae, crustaceans and invertebrate communities of sea
grass beds. The adverse impact of TBT on non target organisms has led to the
introduction of its legislative control in many countries. It was described as one of the
most toxic substances ever deliberately introduced into the aquatic environment.
The Marine Environment Protection Committee of the International Maritime
Organization has proposed a ban on the application of TBT based antifouling paints from
January 1, 2003 and the ban of the presence of such paints on the surface of vessels from
January 1, 2008. This ban is a severe problem for the shipping industry; it presents a
major challenge for the producers of coatings to develop alternative technologies to
prevent fouling organisms. In the wake of these restrictions, researches all over the world
have begun to search for environment friendly antifouling compounds. Safer methods of
biofouling control are actively researched. Copper and its derivative compounds have
successfully been used either in paints and continue to be used as metal sheeting at the
submerged sides of the ship. Research over natural products has shown that marine
organisms are rich sources of such novel and structurally divergent useful compounds.
Marine sedentary organisms including corals and sponges are pointing the way to
formulate natural chemical weapons that might repel the marine foulers without causing
widespread harm. In laboratories around the world, they are under the search light. Their
cells and tissues are yielding a rich harvest of compounds which could function as
antifouling agents. The researchers obtained such two identical lipid compounds from the
outer fleshy tissues of the whip corals. Even bacteria and algae, usually thought to be
fouling organisms themselves, are yielding antifouling compounds. New metabolites
like diterpene methoxy-ent-8(14)-pimarenely-15-one, ent-8(14)-pimarene-15R, 16-diol,
stigmasterol and β-sitosterol, isolated from the roots of the mangrove plant Ceriops tagal
were found to exhibit significant antifouling activities against cyprid larvae of the fouling
barnacle, Balanus albicostatus, with LC50 values all above 10 μg/cm2. Biologists now
realize the need to fully understand the life cycles of so called fouling organisms in order
to design effective, environmental friendly controls. Frequent taking of fishing crafts to
low saline waters like river mouths also found to eradicate the fouling organisms.
Thus the marine fouling effect can be assessed and controlled for the benefit of
human kind around the world.
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