Biofouling of coastal power station pipes and cooling water culverts
presents a problem for the routine operation of these stations. Injection of sodium hypochlorite into the cooling water system is used to control the dominant macrofouler, the common mussel, Myti/us edu/is, which quickly reaches a size large enough to block essential small bore pipes. At the study site, Wylfa Power Station, Anglesey, North Wales, the cooling water system is chlorinated to achieve a concentration of 0.2mg.1"1 NaOCI at the entrance to the condensers during the period when the seawater temperature was above 12°C and when the system is most vulnerable to mussel settlement. To optimise the sodium hypochlorite dosing regime at Wylfa a monitoring programme was undertaken to investigate the presence of mussel larvae in the plankton and to observe the onset, duration and end of mussel spat settlement onto fibrous artificial substrata. In June and August of 1994 and 1995 peak settlements of mussel spat occurred after the seawater temperatures had risen above 12°C. As a result of these findings the period of chlorination was reduced.
The age and growth history of individual mussels collected within and
around the culverts were determined from growth bands present in acetate peels of polished and etched shell sections. During periods of chlorination shell growth is severely reduced resulting in marked changes in shell structure and deposition.
Consequently, growth rates of naturally occurring mussels were substantially
greater than those occurring within the culverts. Mussels experimentally
transplanted into the cooling water system during the chlorination period showed similar banding patterns to those which had settled naturally in the culverts.
The effects of three different chlorination regimes on mussel behaviour and
shell growth were studied in the laboratory in a specially designed tank system
simulating culvert conditions. Chlorination-induced banding patterns were
deposited in the shells of these mussels.