Determining the absolute abundance of dinoflagellate cysts in recent marine sediments II: Further tests of the Lycopodium marker-grain method

Lycopodium clavatum tablets are commonly added as a spike to determine dinoflagellate cyst concentrations in sediments. In this study we investigate the effects of different processing techniques on dinoflagellate cyst concentrations using well-mixed sediment samples from Saanich Inlet, British Columbia, Canada. At the onset of any dinoflagellate cyst investigation, we suggest following the recommendations of Maher (1981) to experimentally adjust the sample size to obtain a ratio close to ~ 2 of dinoflagellate cysts counted to Lycopodium spores counted, in order to obtain reproducible concentrations. Results further show that both oven-drying at ~ 45 °C and freeze-drying are viable, non-destructive techniques yielding reproducible results. Use of warm HCl (40–60 °C) for a short time (30 min) is harmless, whereas treatment with warm HF (40–60 °C) affects the reproducibility of the concentrations. Pre-sieving can result in loss of cysts and/or spike but this can be easily monitored by checking the residue. Perforated metal sieves show more consistent results than the Nitex nylon meshes. The use of 30 second sonication does not affect the reproducibility, and is advised to remove amorphous organic matter. Adding the Lycopodium spike at the end of preparation yields consistently lower concentrations, which were usually not reproducible, suggesting noticeable losses of Lycopodium spores during processing if the Lycopodium spores are added at the beginning. This method can be considered a viable alternative, but the discrepancy should be taken into account.

► We suggest to adjust the ratio of dinocysts to Lycopodium spores counted to ~ 2. ► Drying techniques used in this study were reproducible. ► The use of presieving, 30 s sonication and warm HCl were also reproducible. ► Use of nylon meshes and warm HF can result in a reduction of reproducibility. ► Adding the Lycopodium spike at the end yields consistently lower concentrations.