The toxins produced by some members of the Dinophysis group lead to an illness known as Diarrhetic Shellfish Poisoning (DSP). Diarrhea along with other uncomfortable symptoms (i.e. pain, cramping, vomiting, chills, fever) occurs following consumption of filter feeding shellfish that have accumulate okadaic acid in their tissues. The risk this organism may pose to oyster aquaculture sites within Rehoboth Bay is unknown, so studying its bloom dynamics is essential to ensure a healthy oyster aquaculture industry within Rehoboth Bay.
D. acuminata has been historically identified at high concentrations (>20,000cells/L) in water samples from Rehoboth Bay, Delaware, but the reach of spring blooms and how far they extend to aquaculture sites had not been determined. Temperature, nutrients, and prey abundance can be drivers of Dinophysis blooms. Molecular techniques (PCR) and microscopy have been used to determine the presence or absence of D. acuminata within sediment and water samples from three sites within Rehoboth Bay. A transect was sampled three times in January and one-time early February during an unexpected winter bloom of D. acuminata. The bloom was not strictly isolated to the well monitored site at the Torquay Canal bulkhead (TQB; DNREC RB64) but did not extend into Rehoboth Bay or remain at bloom densities beyond site TQB (10,000-20,000 cells· L-1) for more than 2 weeks. The bloom reached cell density of 191,000 cells· L-1 on January 6, 2020. On January 14, 2020 cell density at site TQB fell to 4,000 cells· L-1 but were at bloom levels (10,000-20,000 cells· L-1) just outside of Torquay Canal, in Bald Eagle Creek at site TQ12 (15,666 cells· L-1) and site TQ11 (11,666 cells· L-1). At TQB site during the winter 2020 bloom event combined nitrate and nitrite levels did not approach the maximum level, but levels increased on January 7, January 14, and February 3. Orthophosphate increased at site TQB on December 23, 2019 and January 14, 2020. There were no significant relationships between cell density and water temperature, chlorophyll-a concentration, conductivity, dissolved oxygen (DO), combined nitrate and nitrite concentrations (NOx), or orthophosphate concentrations (PO43-) during 2020 winter bloom event.
Some dinoflagellates form a resting cyst life stage that allows them to overwinter within benthic surface sediments until spring when conditions become suitable for bloom development while others overwinter in the water column. Sediments were analyzed through PCR to determine presence of Dinophysis using genus specific primers to monitor cyst density or abundance within the sediments during winter months. Samples were taken at Torquay Canal every month from June 2018-February 2020. Samples were taken at Camp Arrowhead and James Farm in summer 2018 (July, August, September) and August 2019. Dinophysis was found in sediments through PCR analysis at Torquay Canal (DNREC Station Code: RB64), Camp Arrowhead (UDCMP Station Code: RB44), and James Farm (DNREC Station Code: IR36). Limited data exist on Dinophysis acuminata for Rehoboth Bay and the results of this study will strengthen resources for monitoring HABs species in Delaware.