UC Santa Cruz

Abstract

Diatoms are important contributors to many biogeochemical cycles in aquatic environments due to their relatively large size and rapid growth rates. Amongst the factors that can limit their growth and productivity, the availability of silicic acid ranks high; the lack of this nutrient in the environment can also be the cause of increased toxicity in the diatom genus Pseudo-nitzschia. For these reasons, it is desirable to track the uptake and utilization of silicic acid by diatoms. Although stable and radio-labeled isotopes of silica exist, they are not commonly used by marine researchers because of the isotope cost and the complexity involved with analysis. PDMPO [2-(4-pyridyl)-5{[4-dimethylaminoethyl-aminocarbamoyl)-methoxy]phenyl}oaxzole] is a low-cost, commercially available fluorophore for monitoring new silica production by siliceous phytoplankton species. PDMPO has been used by a variety of authors to study natural diatom populations for identifying which parts of a cell or which proportion of the phytoplankton assemblage are actively polymerizing silica. These studies however do not acknowledge possible false positive results due to exteriorly bound PDMPO on dinoflagellates and other non-siliceous organisms. Here, we use time series data from the Santa Cruz Municipal Wharf (Monterey Bay California) to show the reactivity of PDMPO with non-silicifying species in a natural, mixed phytoplankton community. Lab experiments using the ionophoric antibiotics monensin and nigericin, show that when used as rinsing agents, the extra cellular binding of PDMPO to various dinoflagellate species can be significantly reduced. We feel that this is an important development for the application of the PDMPO probe to natural community Si kinetics studies in order to reduce false positive data when samples have been digested for quantification via spectrofluorometric analysis.