Sea sparkle is a type of phytoplankton known as Noctiluca scintillans , a free floating algae-like species that can both photosynthesise like a plant, but also ingest particles of food like an animal. When disturbed they emit a blue glow. To support a growth rate of 0. In both experiments, N.
Analysing the qualitative grazing on microzooplankton, nanoplankton and picoplankton, we detected a significant predation on microzooplankton as well as on heterotrophic nanoflagellates and on bacteria. To the best of our knowledge, this is the first experimental evidence of a significant grazing impact of N. In the Gulf of Trieste, the microzooplankton grazing impact on microphytoplankton and particularly on nanoplankton and picoplankton components is very important Fonda Umani and Beran, Noctiluca scintillans can graze on both autotrophic and heterotrophic fractions, thus in a way the species can compete with netzooplankton predators by removing suitable prey items and, on the other hand, it can decrease the grazing pressure of microzooplankton on smaller prey and lower the mortality rates of the smallest planktonic fractions.
Although we observed high ingestion of N. There are indications in the literature that N. Kirchner et al. Smith and Staroscik found a large portion of the bacterial standing stock missing in the presence of a bloom of N. While these publications indicate that grazing on picoplankton in the field is likely, the results of our experiment give the first quantitative estimates of the grazing impact of N.
We want to emphasize that in this instance heterotrophic picoplankton accounted for nearly a quarter of the total ingestion Table II. To calculate the grazing impact exerted by N.
This is a very conservative assumption because of the increase in metabolic needs with rising temperature. In any case, the direct impact of N. May Fonda Umani and Beran, The direct and indirect mortality induced on heterotrophic bacteria must be considered equally important. To conclude, from our field and experimental observations we obtained three main results. In the s, blooms of N. In the s, characterized by decreasing phosphate levels combined with decreasing eutrophication, N.
Noctiluca scintillans in the Gulf of Trieste was able to reproduce actively at low temperatures. The winter presence of N. Noctiluca scintillans was able to live on various planktonic fractions, which range from microzooplankton to bacteria. We would like to thank all the technical and scientific staff at LBM for field sampling and for supplying ancillary data. Thanks are due also to some of S. Two anonymous reviewers provided thoughtful comments on an earlier version of the manuscript.
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