The use of sodium polytungstate for the separation and concentration of living dinoflagellate cysts from marine sediments

Abstract

A method for separating and concentrating living dinoflagellate cysts from marine sediments, using aqueous solutions of the nontoxic chemical sodium polytungstate (SPT), is described. A two-phase, step gradient composed of an upper phase of filtered seawater and a lower phase of aqueous SPT with a specific gravity of 1.30 g cm-3 efficiently separates inorganic particles and organic detritus, retaining living dinoflagellate cysts and intact pollen grains at the phase interface. A consistently higher number of cyst species were identified in treated samples compared to size-fractionated and panned samples, and recovery of living cysts was in excess of 80% of those present in the original sample. Step gradients prepared from SPT have the advantage of a lower viscosity and the potential of higher maximum specific gravities, providing flexibility in the preparation of gradients and selective recovery of live material. The proposed method is rapid (20-30 min), inexpensive, and effective, improving the percentage of living/empty cysts from as little as 4% to as much as 82%. No detectable or selective mortality of particular groups was evident, and 25 species of dinoflagellate were successfully germinated from treated samples, including those of the toxic species Gymnodinium catenatum Graham and Alexandrium catenella (Whedon et Kofoid) Balech. The methods described here present substantial improvements in the time required for and the detection limits of surveys for cysts of toxic dinoflagellates.