Toxicity of copper on marine diatoms,Chaetoceros calcitrans and Nitzchia closterium from Cochin estuary,India

The effects of copper (Cu) toxicity on the growth, pigments, protein, carbohydrate, lipid and antioxidant enzyme activities of two endemic microalgae, Chaetoceros calcitrans and Nitzchia closterium from Cochin estuary were studied and compared. The 96?h median inhibition concentration (IC₅₀) of Cu for C. calcitrans was 143.8?µg?L^?1 and that for N. closterium was 204.5?µg?L^?1. No observable effect concentration (NOEC), lowest observable effect concentration (LOEC) and chronic value of Cu on C. calcitrans were 17.93?µg?L^?1, 31.91?µg?L^?1and 24.92?µg?L^?1 respectively, whereas that for N. closterium were 18.35?µg?L^?1, 36.04?µg?L^?1 and 27.2?µg?L^?1 respectively. Chlorophyll a and c showed significant variation from the control at NOEC in both species. Carotenoid content showed significant increase at LOEC. The chlorophyll a/c ratio significantly decreased at NOEC and LOEC of N. closterium. In N. closterium catalase (CAT) activity showed significant increase at NOEC and LOEC, but in C. calcitrans it varied significantly above LOEC. Protein content showed a significant decrease at NOEC of C. calcitrans. No significant variation was observed for N. closterium. Carbohydrate showed significant variation between the species at NOEC. Lipid content varied significantly at NOEC of C. calcitrans. Chaetoceros calcitrans was observed to be more sensitive to copper toxicity than N. closterium. The metal stress tolerance mechanism of N. closterium and its bioremediation capacity can be established in further studies. This study also provides an insight on the biochemical changes that happened at NOEC.