Aquatic Sciences Meeting, Albuquerque 2001

SS16 Iron Bioavailability and Limitation to Primary Production (Disciplinary Connections)

Date: Monday, February 12, 2001, Time: 4:45:00 PM

Location: Mesilla

Cochlan, W, P, Romberg Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA, USA, cochlan@sfsu.edu

THE HETEROTROPHIC BACTERIAL RESPONSE DURING THE SECOND MESOSCALE IRON ENRICHMENT EXPERIMENT (IRONEX II) IN THE EQUATORIAL PACIFIC OCEAN

The in situ response of heterotrophic bacteria to iron enrichment was followed during the second mesoscale iron-enrichment experiment conducted in the eastern equatorial Pacific during May-June, 1995 (IronEx II). Bacteria abundance (acridine orange direct counts) and 3H-leucine incorporation rates were measured for samples collected from the mixed layer (15 m) over the course of the iron-induced phytoplankton bloom and its decline. Maximal bacterial abundance and productivity estimates were 1.7- and 3-fold greater, respectively, than the average values measured for the heterotrophic bacterial assemblages in the controls (un-enriched waters). Specific growth rates of heterotrophic bacteria increased 3 to 4-fold within the iron-enriched patch. These results demonstrate that iron addition to this high nitrate, low chlorophyll (HNLC) region affect both autotrophic and heterotrophic microorganisms, and that bacterial carbon demand can be met potentially by the 14-fold increase in photosynthetic productivity measured in the iron-enriched surface waters. They do not, however, demonstrate a direct a direct stimulatory response of heterotrophic bacteria to iron enrichment, nor do they suggest that bacteria in this HNLC region are necessarily iron-limited.

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Aquatic Sciences Meeting, Albuquerque 2001

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