Comparison of Alexandrium spp. surface sediment cyst maps from Quartermaster Harbor in 2007 and 2017

Quartermaster Harbor (QMH), in central Puget Sound, has historically been a hotspot for the occurrence of the toxic dinoflagellate Alexandrium spp. and associated summer shellfish bed closures. Alexandrium spp. overwinters as cysts in the sediment and germinates into swimming vegetative cells during the summer when conditions are right. Alexandrium spp. produces neurotoxins which can be concentrated in the tissue of filter-feeding shellfish, which in turn can be fatal to humans if ingested. In 2005, the first Puget Sound wide surface sediment cyst mapping survey found QMH to have the highest concentration of Alexandrium spp. cysts in the sound. A more detailed surface sediment Alexandrium spp. cyst map of QMH was constructed in the winter of 2007/2008 using 24 van veen samples. The highest concentration of cysts was in the inner harbor and central western shore of the outer harbor. Cyst concentration was low near the mouth of the harbor, where tidal currents are highest. Water circulation models of QMH by WADOE found that the QMH inner harbor has a residence time of 1-3 months, which could lead to retention and increased concentration of cysts within the harbor. Puget Sound wide surveys in the winters of 2011, 2012 and 2013 once again found high concentrations of Alexandrium spp. cysts in the surface sediments of QMH, although not as high as previously. The same 24 station detailed survey of QMH cysts and sediments was mapped again in 2017 to see if the distribution pattern of cysts in the bay had changed. The general pattern of relative abundance has remained the same, however the concentration overall has decreased slightly to about half of what it was ten years ago. This may be due to biological bloom dynamics controlling the absolute abundance, while physical forcing conditions determine the relative concentration spatial distribution