A natural exposure experiment on short-term species-selective aerobic degradation of dinoflagellate cysts

Although studies have shown that organic-walled dinoflagellate cysts (dinocysts) can undergo species-selective aerobic degradation, the alteration rate of this process is not known. Here we provide data on the decay rates of dinocyst from a degradation experiment in which sediment samples of Holocene age from (a) anoxic Namibian shelf and (b) anoxic part of the eastern Mediterranean S1 sapropel have been exposed to oxic and anoxic conditions in natural environments. The two types of sediment were stored in bags composed of a dialyse membrane that allows oxygen penetration but prevents bacterial exchange. Sediment bags were placed in open containers connected to sediment traps and moored for 15 months in anoxic brines and oxic intermediate waters of the Urania and Bannock Basins areas. Within the short experimental time (15 months), exposure to oxygenated waters resulted in a 24% to 57% reduction in concentration of cysts attributable to Brigantedinium spp. and Echinidinium granulatum. Other taxa such as Spiniferites spp ., Lingulodinium machaerophorum and Echinidinium spp. appear to be less sensitive. A slight increase in cyst concentration is observed for Nematosphaeropsis labyrinthus, Echinidinium aculeatum, Operculodinium israelianum, and Impagidinium aculeatum, indicating that these cyst species are more resistant to aerobic degradation. Exposure to anoxic conditions has not lead to detectable differences between initial and exposed composition and concentration. Our study is the first to document that species-selective degradation of dinocysts in oxygenated natural environments is a rapid process that changes considerably dinocyst concentrations and assemblages.