Empirical Relationships between Bacterial Abundance and Chlorophyll Concentration in Fresh and Marine Waters

Abstract

A strong, positive empirical relationship was found between bacterial abundance and chlorophyll concentration in fresh and marine waters. Freshwater and marine linear regression equations are statistically indistinguishable. The overall equation is log AODC = 5.867 + 0.776 log chl a, r 2 = 0.88, where AODC (acridine orange direct count) is the number of bacteria per millilitre and chl a is micrograms of chlorophyll a per litre. It is apparent that planktonic bacteria and algae are tightly linked in lakes and the sea. The slope of the regression line, however, shows that bacterial numbers do not increase as rapidly as algal biomass with an increase in nutrient concentration. We suggest that this disproportionately smaller increase in bacterial numbers need not signify a smaller role for bacteria in lake metabolism with increasing nutrient availability, if bacterial productivity per unit bacterial biomass increases as total bacterial biomass increases between systems.