Purcell, J. E. University of Maryland Center for Environmental Science, purcell@hpl.umces.edu
Bamstedt, U. E. University of Bergen, ulf.baamstedt@ifm.uib.no
Bamstedt, A. University of Bergen,

 
PREY, FEEDING RATES, AND ASEXUAL REPRODUCTION RATES OF THE INTRODUCED OLIGOHALINE HYDROZOAN MOERISIA LYONSI
 
Moerisia lyonsi medusae and benthic polyps were found at 0 to 5 ppt salinity in the Choptank River subestuary of Chesapeake Bay. The medusae and polyps are small (< 5 mm and 1 mm, respectively), and may occur widely but unnoticed in estuaries. Medusae consumed copepod nauplii and adults, but not barnacle nauplii, polychaete and ctenophore larvae or tintinnids. Predation on copepod adults was maximum (1 copepod/ medusa/hour) at 30 copepods/liter. Feeding rates on copepod nauplii were higher than on adults and showed no saturation at 1-65 nauplii/liter. Experimental mesocosms were colonized by M. lyonsi during spring and summer in 4 years, reaching extremely high densities (< 13.6 medusae/liter). Densities of zooplankton were low when medusa densities were high, and estimated predation by M. lyonsi could have limited copepod populations in the mesocosms. Polyps asexually produced buds that developed into polyps or medusae. Production rates increased with increasing prey availability, from 9.5 + 2.5 buds/polyp at 1 copepod/day, to 146.7 + 8.3 buds/polyp at 8 copepods/day during a 38 d experiment. The colonizing potential of this hydrozoan is great given the high rates of asexual reproduction, fairly wide salinity tolerance, and resistant cyst stage.
 
Day: Wednesday, Feb. 3
Time: 04:45 - 05:00pm
Location: Eldorado Hotel
 
Code: SS18WE0445E