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.

*****