Sullivan, B. K.. University of Rhode Island, bsull@gsosun1.gso.uri.edu
Klein-MacPhee, G. K.. University of Rhode Island, gracemac@gsosun1.gso.uri.edu
Klos, E. University of Rhode Island, klos@gsosun1.gso.uri.edu

 
GROWTH AND PREDATION BY PLANKTONIC HYDROIDS: A CLEAR CASE OF MIXING AND TURBULENT CONTROL TESTED IN MESOCOSMS
 
Floating colonies of hydroid polyps are hugely abundant (up to 10/liter) on Georges Bank. Their distribution is restricted to the region inshore of the tidal mixing front; they are rare in deeper, seasonally stratified waters. We propose that turbulence and mixing in the well-mixed region results in successful growth and maintenance of hydroids in the water column where they prey on microzooplankton and larval fish. We have tested this hypothesis in 13m3 enclosures with turbulence (produced by horizontal rotors) simulating levels measured in situ on Georges Bank. Turbulence in the mesocosms was measured with an acoustic Doppler velocimeter; turbulent energy dissipation rates were calculated by spectral analysis. Turbulent energy power spectra compared favorably with the theoretical power spectrum of frequencies in the form f-5/3. Growth rates of hydroids were highest in enclosures with turbulence simulating the well-mixed region of Georges Bank. Predation mortality of juvenile copepods and larval cod was significantly greater at higher turbulence levels. Increased growth of hydroids was probably due to higher ingestion rates of microzooplankton in the well-mixed mesocosms. High mortality rates of fish larvae in well-mixed mesocosms could be explained by increased numbers of hydroids as well as increased predator-prey contact rates.
 
Day: Tuesday, Feb. 2
Time: 04:00 - 04:15pm
Location: Hilton of Santa Fe
 
Code: SS01TU0400H