Revilla, M. M.. Universidad del País Vasco,
Iriarte, A. M.. Universidad del País Vasco,
Madariaga, I. I.. Universidad del País Vasco,
Orive, E. E.. Universidad del País Vasco, gvporage@lg.ehu.es

 
SHIFT FROM AUTOTROPHY TO HETEROTROPHY IN A TEMPERATE ESTUARY
 
Rates of size-fractionated plankton respiration and bacterial and phytoplankton production were measured in surface and bottom waters near monthly in 1996 in three estuarine zones of contrasting features in the Urdaibai estuary. In the upper more eutrophic segment rates of bacterial and phytoplankton production and respiration peaked during periods of moderate to low river discharge. In this case, bacterial net production in surface waters accounted for less than 25% of total net particulate matter production whilst it was higher than 50% during periods of low phytoplankton production. In the bottom layer a net heterotrophy was always found. Bacterial growth efficiency was higher than 60% during periods of peak production. Rates of bacterial and phytoplankton production and respiration decreased at intermediate salinities where net phytoplankton production accounted generally for more than 50% of total net particulate matter production at both surface and bottom waters. At the lowere more oligotrophic estuary a strong correlation was found between bacterial production and nutrient concentrations but no clear relationship was found between bacterial and phytoplankton metabolism.
 
Day: Thursday, Feb. 4
Time: Poster
Location: Sweeney Center
 
Code: CS57TH1224S