Associations of the Carbonate System and Nutrient Levels with Growth of Prymnesium parvum

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In natural aquatic systems algal growth is typically controlled by the nutrient concentrations present in the water. In this study we investigated or examined the association of the carbonate system with the growth of Prymnesium parvum, a well-known harmful algal species. Prymnesium parvum was grown in batch cultures under six different experimental treatments varying in phosphorous and nitrogen levels (f/2, high; and f/8, low) and DIC concentrations (high, medium, and low). Cultures were continued until they reached stationary phase (maximum densities). Our working hypotheses are that under high nitrogen and phosphorous conditions, 1) populations will grow to higher cell densities and will be consequently accompanied with higher DIC consumption, high pH and lower levels of pCO2, and 2) low levels of initial DIC will become limiting for P. parvum growth. Results show that by day 24, compared to the low nutrient treatments, all high nutrient treatments had greater cell densities that lead to lower DIC concentrations, higher pH levels, and lower pCO2. Even though all treatments showed pCO2 undersaturation by day 24, undersaturation in the high nutrient treatments was greater than the low nutrient treatments. The first working hypothesis for this study that under high nutrient conditions P. parvum would grow to higher cell densities and will be consequently accompanied with higher DIC consumption, high pH, and lower levels of pCO2 was confirmed in both trials. However, the second working hypothesis that carbon limitation would occur under high nutrient and low initial DIC was confirmed in only the second trial; namely, that the low initial DIC concentration will limit the growth of P. parvum under high nutrient conditions. It is possible that the initial DIC concentration used was not low enough to obtain consistent results of carbon limitation on P. parvum growth. The findings in this study have improved our understanding of the relationship between inorganic carbon and P. parvum growth in waters of different nutrient levels.

Prymnesium parvum, dissolved inorganic carbon, partial pressure of carbon dioxide (PCO2), eutrophication