Dr. Carmelo Tomas, UNC-Wilmington (hosted by Astrid Schnetzer) |

Title: Mystery Fish Killer in Delaware, U.S.A.

Abstract: During the summer months of 2000, more than 10 fish kills were observed in Delaware’s Inland Bay area. The causative agents were unknown and during the last fish kill an extensive bloom of an unknown phytoplankton species was observed. The concentrations at the time of the bloom was 10 7 cells/L consisting primarily by a previously undescribed photosynthetic flagellate. The blooms persisted throughout the period from mid-August through October before populations declined and disappeared by late November. In subsequent years, this species formed blooms each summer but never developed the populations of the summer 2000 bloom. The unknown species was brought into culture in 2004 and was subject of an extensive series of studies to determine its identity, toxicity and ecophysiology. Sample water from the 2000 bloom was found to contain brevetoxins, commonly found in Karenia brevis the dinoflagellate that routinely causes toxic red tides in Florida. No Karenia species were observed in the bloom waters. Examination of temperature/salinity optima established this species as preferring warmer waters (>18°C) and mid range salinities from 20 to 30. It would not grow at salinities below 10 or above 30. Nutrient studies indicated urea as a preferred nitrogen source over ammonia and nitrate. Pigment analyses including two-dimensional NMR established a new pigment for this species confirmed from culture and natural samples.

Electron microscopy defined the ultrastructure of this species to be a heterokontophyte but of unknown identity. Molecular studies of LSU, SSU, ITS, 8.5 S, rubisco, cox and secondary structure of the ITS all indicated it was a new monophyletic taxa. Toxicity assays were inconclusive but gave some suggestion of brevetoxin like compounds present in the cultures.

The equivocal toxin data urged us to look further and in 2007, an unusual Karenia species was found in the Inland Bays region. Karenia papilionacea and Karenia selliformis were positively identified in natural samples from the Inland Bays. The presence of the toxins and their role in the fish kills will be discussed.