Institution: | a Bigelow Laboratory for Ocean Sciences, McKown Point Road, West Boothbay Harbor, ME 04575, USA b Mel Fisher Maritime Museum, Key West, FL 33040, USA c Harbor Branch Oceanographic Institution, Fort Pierce, FL 34936, USA |
Abstract: | In studies of primary production of the open ocean, the measurement of new production is often considered a measure of the degree of eutrophication. Because of new research this is questionable, which in our opinion, calls for a refinement to the original concept. We believe that the measure of variable fluorescence is pivotal to a new understanding. Our research enforces the growing conviction that the measurement of Fv/Fm can be interpreted as an analogue for nutrient stress. We measured variable fluorescence in axenic cultures at the CCMP at the Bigelow Laboratory. The Fv/Fm of cultures, upon transfer to new media reached a maximum followed by a decline after approximately 30 days. The rate of decline does not appear to be species specific. Most of the clones remained relatively high after 30 days. The high Fv/Fm values observed in nutrient-replete cultures are not characteristic of the oligotrophic surface waters off Florida and the Bahamas, but are approached in the eutrophic waters of the Gulf of Maine. In contrast, Fv/Fm measurements of attached macroalgae and coral zooxanthellae are characteristically much higher than microalgae of either oligotrophic or eutrophic regions. Accordingly, we advance the case for interpretation of Fv/Fm in terms of nutrient stress in ecological studies and advocate that the old concept of new production should be modified. |