A. Map of the Delmarva peninsula, showing both Chesapeake Bay and coastal bays. Boxed in the inset is the study site described in this work, and is shown in greater detail in Figure 1B. B. Water quality monitoring stations in a Maryland and Virginia coastal bay ecosystem. From April through November of 2010 and 2011, sediment and water samples were collected from 18 sites south of the Ocean City inlet, and adjacent to the Assateague Island National Seashore Park. The sampling stations are monitored yearly by the National Park Service water quality program. DNA was extracted from these samples for subsequent PCR analysis to monitor the presence of Hematodinium sp. Figure courtesy of the National Park Service. Sites: 1, Commercial Harbor; 2, Verrazano Bridge; 3, Newport Bay; 4, Trappe Creek; 5, Public Landing; 6, Whittington Point; 7, Taylor’s Landing; 8, Wildcat Point; 9, Greenbackville; 10, Sinnickson; 11, Chincoteague Channel; 12, Assateague Channel; 13, Tom’s Cove; 14, Johnson’s Bay; 15, Cedar Island; 16, South Point; 17, Ocean City Inlet; 18, Snug Harbor.