Cell density, chemical composition and toxicity of Chrysochromulina polylepis (Haptophyta) in relation to different N:P supply ratios |
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Authors: | N Johansson E Granéli |
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Institution: | (1) Department of Marine Ecology, Ecology Building, University of Lund, S-223 62 Lund, Sweden, SE;(2) Department of Marine Sciences, University of Kalmar, P.O. Box 905, S-391 29 Kalmar, Sweden, SE |
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Abstract: | The influence of different N:P supply ratios on cell accumulation, chemical composition and toxicity of the marine haptophyte
Chrysochromulina polylepis was examined in semi-continuous cultures. A non-axenic strain of C. polylepis was exposed to five different N:P supply ratios (N:P = 1:1, 4:1, 16:1, 80:1 and 160:1, by atoms), in order to create a range
of N- and P-limited conditions. The toxicity per cell in C. polylepis was determined on four occasions at steady state cell density using the haemolytic activity of the cells expressed as saponin
nanoequivalents. Haemolytic activity was demonstrated in all treatments, and increased in the algae when cell growth was nutrient
limited (N:P = 1:1, 4:1, 80:1 and 160:1), compared to cells grown under non-limiting conditions (N:P = 16:1). This occurred
regardless of the growth-limiting nutrient (N or P) and became more pronounced as nutrient limitation increased. In P-limited
cultures the haemolytic activity per cell increased linearly with the cellular N:P ratio, whereas the N-limited cultures showed
an opposite trend. The haemolytic activity per cell showed an inverse relationship with both cellular N and cellular P content.
Cells limited by P showed a higher haemolytic activity than cells limited by N. The results suggest that toxicity in C. polylepis is strongly influenced by the physiological state of the algae. This may partially explain the large variability previously
observed in the toxicity of C. polylepis blooms. The potential ecological significance of our findings is also discussed.
Received: 18 November 1998 / Accepted: 5 July 1999 |
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