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  • 1
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    Oxford Univ. Press
    In:  Journal of Plankton Research, 26 (3). pp. 357-369.
    Publication Date: 2019-09-23
    Description: The so-called ‘turbulence incubator’ overcomes an essential disadvantage of static in situ incubations where at high irradiances an artificial photoinhibition is caused by neglecting turbulent mixing in the upper water column. It is operated on deck and simulates the changing light conditions for vertically mixed phytoplankton cells by moving the sample bottles horizontally through a circular water bath covered by a glass lid of neutral optical density filters. In this way the exponentially decreasing irradiance within the euphotic zone is simulated and photoinhibition near the surface is avoided. A crucial point is the choice of revolution rate for simulating turbulent mixing under natural conditions. The incubator is characterized by its handy size, a relatively simple and inexpensive construction and a battery-driven motor. It can thus even be operated on small vessels without an electric generator. The incubator is especially suited for vertically mixed waters such as shallow bays, tidal estuaries and rivers. Its reliability was successfully tested by a simultaneous comparison with in situ measurements at various stations representing different water types and environmental conditions, ranging from the turbid River Elbe to the clear open Baltic Sea. In 9 out of 11 experiments, higher primary production rates were obtained in the turbulence incubator than in static in situ incubations. The majority of the latter were characterized by a pronounced photoinhibition in the upper two incubation depths representing the 100 and 50% light levels. The average rate increase amounted to 22%, with a range between 11 and 53% depending on light attenuation and irradiance.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    Publication Date: 2018-05-30
    Description: In an assessment of non-indigenous species transported by international ship traffic to German waters, commissioned by the German Federal Environmental Agency, the survival of tropical plankton organisms in ballast water was studied by accompanying a container vessel on its 23-day voyage from Singapore to Bremerhaven in Germany. Two tanks, one filled off Singapore and the other off Colombo, Sri Lanka, were monitored for their phyto- and zooplankton content by daily sampling. As already reported in previous studies, species abundance and diversity, especially of zooplankton, decreased sharply during the first days, and only a few specimens survived the whole cruise. The contents of the Colombo tank, however, changed dramatically during the last week. The harpacticoid copepod, Tisbe graciloides, increased its abundance by a factor of 100 from 0.1 to 10ind. l–1 within a few days. This is the first time that a ballast water organism has been found to multiply at such a high rate. Opportunistic species such as Tisbe are apparently able to thrive and propagate in ballast water tanks under certain conditions. Ballast water tanks may thus serve as incubators for certain species depending on their characteristics.
    Type: Article , PeerReviewed
    Format: text
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