EFFECTS OF LIGHT, TEMPERATURE AND SALINITY ON THE GROWTH-RATE OF HARMFUL MARINE DIATOMS, CHAETOCEROS-CONVOLUTUS AND C-CONCAVICORNIS THAT KILL NETPEN SALMON

Chaetoceros convolutus and C. concavicornis have been implicated in th e death of salmon in netpens in the Pacific Northwest by damaging the salmon's gills. To better understand how environmental factors affect the distribution of these two species, the interacting effects of ligh t, temperature and salinity on growth rate were examined by growing th ese species under a range of temperatures (4-18-degrees-C), light (10- 175 mumol photon m-2 s-1) and salinities (10-30 parts per thousand). F or C convolutus, the growth rate showed a hyperbolic relationship with irradiance at 8, 14 and 18-degrees-C and light saturation occurred at 9, 14 and 20 mumol photon m-2 s- 1 respectively. At 4-degrees-C for C . convolutus and 8-degrees-C for C. concavicornis, cells grew at mu(ma x), even at the lowest irradiances tested (10 mumol photon m-2 s-1). F or C convolutus, the amount of light required to saturate growth rate increased with temperature in an approximately linear fashion. The Q10 was 1.88, calculated by averaging over both species. C. concavicornis was the more euryhaline species growing at salinities as low as 17.5 parts per thousand, while C. convolutus grew only at 25 parts per thou sand and above.