Bioassay procedures for marine phytoplankton with special reference to chlorine

In general, bioassay procedures for phytoplankton have involved measurement of population enumerative parameters (such as specific growth rate, biomass, or chlorophyll a concentration) or population functional parameters (such as 14C uptake) in static cultures exposed to a toxicant. From these data, an estimate is then made of the concentration of the toxicant having some defined effect. Hirayama and Hirano (1970) used the experimental design shown in Fig. 1 to assess the effects of a 5 or 10 min. exposure to chlorine on phytoplankton by measuring subsequent population growth rates. Skeletonema was found to be more sensitive than Chlamydomonas, with the major effect being an increase in the time elapsed before measurable growth occurred. In these experiments, high population densities and nutrient enrichment were employed raising the possibility that the populations were capable of tolerating higher chlorine doses than might natural populations. Roberts and Diaz (1976) measured primary productivity potential of populations of four phytoplankton species (Tetraselmis suecica, Pseudoisochrysis paradoxa, Pyramimonas virginica, and Nannochloris occulatus) exposed to logarithmic chlorine dose series at three temperatures and three salinities (Fig. 2). The cultures were established in filtered pasteurized nonenriched water at cell densities comparable to wild phytoplankton populations (103 cells/ml). The relationship between carbon uptake (expressed as percent of control) and log chlorine dose was often non-linear, whereas the relationship between assimilation ratio (expressed as percent of control) and log chlorine dose was linear (Fig. 3). (Assimilation ratio as used here means the carbon uptake rate/chlorophyll a concentration.) Fig. 4 shows typical results for combined temperature/chlorine effects. Deviation from the original culture temperature tended to increase the sensitivity to chlorine. An unex-