Kononen, K. Finnish Institute of Marine Research, kaisa.kononen@nessling.fi
Huttunen, M. Finnish Institute of Marine Research, Finland., Maijahut@fimr.fi
Kanoshina, I. Estonian Marine Institute, inga@phys.sea.ee
Laanemets, J. Estonian Marine Institute,, jaan@phys.sea.ee
Moisander, P. Institute of Marine Sciences,, pia@marine.unc.edu

 
HORIZONTAL, VERTICAL, AND TEMPORAL VARIABILITY OF A DINOFLAGELLATE-CYANOBACTERIUM COMMUNITY IN A CHANGING HYDRODYNAMICAL REGIME AT THE ENTRANCE TO THE GULF OF FINLAND
 
A 12-d multidisciplinary research cruise was carried out in late July 1996 at the entrance to the Gulf of Finland. The summer was exceptionally cold in the Northern Europe and the seasonal bloom of cyanobacteria was delayed with ca.2-3 weeks in the study area. Instead, a red tide formed by Heterocapsa triquetra developed in the Northern Baltic Sea and the Gulf of Finland. The daily hydrophysical surveys revealed a variety of meso-scale phenomena: downwelling, jets, and anticyclonic and cyclonic eddy. Vertical and temporal variability of nutrients, size-fractionated primary production, nitrogen fixation and phytoplankton species composition was studied at a fixed station. In addition, horizontal variability of nutrients and two dominating phytoplankton species, a dinoflagellate Heterocapsa triquetra and a cyanobacterium Aphanizomenon flos-aquae, was studied at 5 m depth within an area of 15 km x 25 km. The variability (CV%) of the abundance different phytoplankton species, chlorophyll a and primary production at the fixed station was always highest in the > 20 Ám size group organisms and could be explained by the meso-scale hydrodynamical processes. The maximum abundance of Heterocapsa developed in the anticyclonic eddy whereas high abundance and nitrogen-fixation activity of Aphanizomenon flos-aquae was related to a less saline water mass advecting in the periphery of a strong jet. The results pointed out that 1) abundance and activity of larger, bloom-forming species, especially, is explained by meso-scale hydrodynamics, 2) phytoplankton species' appear as a spatial mosaic formed by the interplay of water masses and that 3) information about meso-scale hydrodynamics is required for the interpretation of results on pelagial biology at fixed station.
 
Day: Thursday, Feb. 4
Time: 11:45 - 12:00pm
Location: Hilton of Santa Fe
 
Code: SS04TH1145H