Gilmour, C. C.. The Academy of Natural Sciences Estuarine Res. Ctr., gilmour@acnatsci.org
Ward, P. C.. The Academy of Natural Sciences Estuarine Res. Ctr., ward@acnatsci.org
Bennett, L. The Academy of Natural Sciences Estuarine Res. Ctr.,
McManus, G. University of Connecticut, mcmanus@uconnvm.uconn.edu

 
INTERACTING EFFECTS OF NUTRIENTS AND TRACE METALS ON MICROBIAL FOOD WEBS IN ESTUARINE ENCLOSURES
 
We examined the effects of multiple stresses on estuarine microbial food webs as part of the COASTES project. Eight 1000L mesocosm experiments over three years were conducted using the Patuxent River, MD, as source water. Mesocosms were amended with nutrients, metals, both or neither. Among experiments, the effect of toxics was more variable than the effect of nutrients. Inhibition by toxics occurred more frequently during spring. Generally, the response of bacteria and heterotrophic nanoflagellates (HNAN) mirrored that of the phytoplankton, although nutrients had additional direct effects on bacterial growth under some conditions. The nutrient-stimulated transfer of carbon from phytoplankton to bacterioplankton was somewhat less than in other mesocosm studies. During 3 of 8 experiments, the addition of trace metals at or below water quality criterion concentrations (Cu 5 ppb; As 10 ppb; Cd 0.5ppb) decreased the abundance of bacterioplankton and HNAN relative to control tanks. Metal effects were most pronounced in tanks to which nutrients were added. Densities of bacteria and HNAN were more sensitive to metals than bacterial production or bactivory. Metals appear to affect the microbial food web through decreases in bacterial growth efficiency rather than through direct effects on HNAN grazing rates.
 
Day: Friday, Feb. 5
Time: 04:15 - 04:30pm
Location: Sweeney Center
 
Code: SS28FR0415S