|Biofoulers in Tuticorin Bay, Tamil Nadu, India
Sacred Heart Marine Research CentreSister Avelin Mary, Director
The barnacle (Balanus amphitrite) is the most serious fouler faced by pearl oyster farmers in India. This barnacle settles and grows on the shells of the pearl oysters, while boring organisms riddle through the shells, rendering them weak and fragile. B. Amphitrite is perhaps the most ubiquitous fouler worldwide having been carried by ships from port to port for millennia. In Karrapad Cove, Tuticorin Bay (India), fouling is year round, with some seasonal trends as shown in the figure below.
Seasonal changes in amount of barnacle, algal and tubeworm fouling on
Following the barnacle in terms of fouling are the mollusks, Avicula vexillum and Crassostrea sp. The tubiculous polychaetes (Hydroides sp.) have not been found to be significant, and they appeared in pearl oyster farms only in January.
The worm is about 3 inches in length. The crown of the branchiae is long and slender, radiating from the united base. It builds calcareous tube often in coiled masses. The projecting heads have two fan shaped series of branchiae with plume like pinnae fifteen to eighteen in number with a color pattern variegated with pink. A dorsal filament on each fan has been modified into an operculum, one of which is fully developed, the other rudimentary. It is seen to be a double, handsomely patterned structure composed of two super imposed star like discs, the lower being the larger and made up of twenty five or more pieces like a vase or flower cup surmounting a stem. The body of this species is of a reddish orange colour. Hydroides elegans is a tough and cosmopolitan serpulid fouler.
Very common on calcareous structures (shell,coral, calcerous algae, barnacles). Excurrent and incurrent papillaeproject out of substratum in living condition, but are highly contractile and only pores on substratum visible out of water. Pores are 0.5-2.0 mm. in diameter but subject to considerable variation. Larger pores accommodate excurrent and smaller, incurrent papillae. Papillae are green, golden yellow or red when live. Chambers found inside substratum are small, 2 to 5 mm. in diameter, but subject to considerable variation. All members, at least in early life, bore into calcareous matter and thus, are a menace to commercially important mollusks and coral reefs. There are 32 species belonging to this family in the Indian seas (Thomas 1979). They cause considerable damage to the pearl, chalk, and oyster beds of the Gulf of Mannar and Palk Bay in India.
Plate corals have never been observed at the test site until 2010. They appear white and flattened, tending to cover a small area on uncoated or panels coated with protective coatings without antifoulings. The plate corals grow fast for a month and slow down or vanish altogether. Since this is the first year it has been observed, their occurrence may represent some environmental changes in the habitat enabling them to colonize surfaces.
The figure shows the percentage of such panels under immersion testing with coral fouling. Only a small proportion of the panels, at best 200% at peak occurrence in November 2010. The fouling appears seasonal and abruptly terminates. We will update the graph if they reappear again later in 2011.
Incidence of plate corals in control test panels under static