Microzooplankton and their herbivorous activity in the northeastern Atlantic Ocean

The grazing impact of protists on phytoplankton primary production in a highly oligotrophic area of the subtropical north-east Atlantic, south-east of the Azores, was studied using the dilution method. The phytoplankton community in the experiments, analysed by flow-cytometry, was dominated by Prochlorococcus and Synechococcus although larger phototrophic groups, beyond flow-cytometry sensitivity, were also present. The microzooplankton community was dominated by small gymnodinoid dinoflagellates and aloricate ciliates, and its biomass was low, averaging 0.7 mg C m -3. We measured average phytoplankton growth rates of 0.76 and 0.22 d -1 in surface waters and in deep chlorophyll maximum (DCM) waters respectively; mortality rates due to protists grazing were 0.58 and 0.22 d -1 , respectively. We did not find significant differences in growth and mortality rates of the different phytoplankton groups, i.e. Prochlorococcus, Synechococcus or nanoeukaryotes; thus no prey preference was apparent from the results. Protists consumed on average 79 and 109% of primary production in surface and DCM waters respectively, controlling phytoplankton growth in the area. The net primary production closely oscillated around zero in the chlorophyll a analyses and was positive in the flow-cytometry analyses, suggesting a balanced or slightly autotrophic phytoplanktonprotist compartment.

Section: Discussionsupporting

confidence: 80%

Protist control of phytoplankton growth in the subtropical north-east Atlantic

Quevedo

Anadón²

2001

“…These studies demonstrated that microzooplankton were important controllers of the fate of phytoplankton production in surface waters between 47 and 60°N, and between 20 and 21°W. Results from experiments using the dilution technique of Landry & Hassett (1982) showed that microzooplankton herbivory accounted for up to 115% of daily phytoplankton production (Burkill et al 1993, Gifford et al 1995. However, these studies focused on the spring and summer phytoplankton communities in northern, eutrophic waters and did not investigate the role of microzooplankton grazing in the southerly, oligotrophic region of the NE Atlantic.…”

Section: Introductionmentioning

confidence: 92%

“…Estimates of their grazing impact indicate that they can control phytoplankton production (e.g. Gifford 1988, Burkill et al 1993) and play a significant role in the fate of bacteria (e.g. Weisse & Scheffel-Möser 1991) and in the regeneration of nutrients (e.g.…”

Section: Introductionmentioning

confidence: 99%

Microzooplankton grazing activity in the temperate and sub-tropical NE Atlantic: summer 1996

Stelfox-Widdicombe¹,

Edwards²,

Burkill³

et al. 2000

) and oligotrich ciliates (0.7 µg C l -1 ) were more important at the southerly station. Tintinnids and 'other' ciliates contributed less to the total microzooplankton abundance or biomass. We conclude that microzooplankton formed a significant component of the food web in the NE Atlantic and were important controllers of phytoplankton production, particularly in temperate waters, during this investigation period. Our data suggest that microzooplankton grazing did not control the picoplankton production in the oligotrophic sub-tropical NE Atlantic during the summer, and this may be attributable to the dominance of Prochlorococcus spp.

“…At a 20" W transect from 47" N to 60" N, Burkill et al (199313) found that the biomass losses due to microzooplankton herbivory were positively related to phytoplankton biomass as well as seawater temperature. This result is confirmed by our experiments (Fig.…”

Section: Microzooplankton Grazingmentioning

confidence: 99%

Microzooplankton grazing and nitrogen supply of phytoplankton growth in the temperate and subtropical northeast Atlantic

Gaul¹,

Antia²,

Koeve³

1999

Serial dllution experiments were conducted on JGOFS-North Atlantic cruise of RV 'Meteor' M36/2 at a 20" W transect in June and July 1996 to assess the role of m~crozooplankton grazing and nitrogen supply in controlling phytoplankton stocks in the subtropical and temperate northeast Atlantic. Rates of m~crozooplankton grazing ranged from 0. sources in nitrate-rich waters of the muted layer at 54" N and at the nitracline at 47" N, whereas nitrogen regeneration dominated at the nitrate-depleted surface waters at 47" N. However, In the deep chlorophyll maxlma at 33" N and 40" Y phytoplankton growth was primarily maintained by n~t r o g e n regeneration, although external nitrogen was sufficiently available. The recycling efficiency of the microb~al community was d e f~n e d as the ratio of regenerated growth yield to herbivorous grazing loss. Efficiencies of -100":1 under post-bloom situations indicated tight coupling of predation, nitrogen supply and phytoplankton growth. We suggest that n~icrozooplankton grazing has a high potential for nitrogen supply and biomass control of phytoplankton communities during summer in the temperate and subtropical northeast Atlantic.