Historical Abundance of the Harmful Dinoflagellate Alexandrium in a Sediment Core from Quartermaster Harbor, Puget Sound, Washington

Alexandrium is a dinoflagellate that produces saxitoxin, known to cause paralytic shellfish poisoning from consumption of exposed shellfish. Due to the possibility of toxicity and potential economic impacts, the presence of Alexandrium is regularly monitored throughout the Puget Sound. Alexandrium spends part of its life cycle as a cyst in the sediment before germinating to become a free-swimming dinoflagellate Alexandrium cysts in surface sediments are used to determine the present spatial distribution of this organism, while cyst concentrations in sediment cores can be used to evaluate historical presence and temporal variability. A research project from 2005, funded by NOAA’s ECOHAB program, has shown that surface sediments in Quartermaster Harbor (QMH), a harbor with low flushing rates due to is geographical orientation, had the highest abundance of Alexandrium cysts than anywhere in Puget Sound. In July 2010, sediment cores were collected from five locations in Puget Sound to determine the historical distribution of Alexandrium. The purpose of this study looks at a 202 cm Kasten core collected from the inner harbor of QMH. Sediments were prepared by sieving material between 20 and 90 µm, and staining with Primulin. Prepared sediment was then observed under epifluorescence using an FITC filter on a compound microscope. Results show maximum cysts/mL sediment near the surface, regressing to 0 cysts/mL sediment below 30 cm. The core was characterize by analyzing the grain-size distribution and organic content of each sub-sample of the core in order to determine if there is a relationship between cyst abundance/presence and these properties. 210Pb dating was completed in order to correlate cyst abundance and local changes to the harbor. Understanding the historical distribution of Alexandrium cysts is important in tracing its spread throughout the Puget Sound