Laboratory Evaluation of the Toxicity of Chlorine to the Fouling Hydroid Cordylophora caspia

The brackish water hydroid, Cordylophora caspia (Pallas) (syn. Cordylophora lacustris Allman) is an important fouling animal in industrial cooling water systems. However, there are no published studies regarding the response of this species to chlorination, which is a widely used antifouling method. The effects of different chlorine concentrations (0.1-1 mg l^{m 1} total residual chlorine) on growth rate (k) of C. caspia were studied in the laboratory. The results show that chlorine is effective at relatively low concentrations (above 0.1 mg l^{m 1} residual chlorine). The growth rate of C. caspia at different chlorine concentrations was dose-dependent. An average decrease of 23% in the growth rate was observed at 0.1 mg l^{m 1} residual chlorine when compared to control experiments, over a period of 7 d. No growth was recorded at 1 mg l^{m 1} residual chlorine, indicating threshold levels of residual chlorine on C. caspia. The size (length and width) of hydranths decreased significantly as the chlorine concentration increased. Complete hydranth degeneration in 3 d was observed at 1 mg l^{m 1} residual chlorine. The results also showed that temperatures >30°C (but not lower temperatures) hastened mortality due to chlorine. The combined use of chlorination (0.2 mg l^{m 1} residual chlorine) and heat (30°C) decreased the growth rate of C. caspia by more than 59% when compared to 0.2 mg l^{m 1} at 20°C.

Keywords:

• Biofouling
• Hydroids
• Cordylophora Caspia
• Chlorine
• Growth Rate