Menu

Experiments by Invited Researchers

 

Stratification and food web dynamics in marine pelagic environments.

Project acronym: H+-NTNU-01-StratWeb
Name of Group Leader: Philippe Pondaven
User-Project Title: Stratification and food web dynamics in marine pelagic environments.
Facility: Sletvik Field station
Publications: Patrick_Fink_etal_lipids_in_the-ocean__meetings_2018.pdf
Pondaven_etal_Proceedings_HYDRALAB_Joint_User_Meeting.pdf

From August 23 th to September 15 th 2017, a team of marine biologists & ecologists from the University of Munich, the University of Cologne and the University of Brest was visiting the Sletvik Field Station (NTNU, Norway) to study the dynamics of plankton communities. This work was supported by funding from the HYDRALAB+ project, and a team from the NTNU

team during the STARTWEB experiment in the Bay of Hopavågen (August-September 2017) - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Picture 1 - Team during the STARTWEB experiment in the Bay of Hopavågen (August-September
2017) - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink

The team has investigated the effects of increasing water column stratification on plankton dynamics experimentally by performing mesocosm experiments in the Bay of Hopavågen (Picture 2). The mixing depth of the water column was experimentally manipulated and we have followed the consequences of the manipulations for the plankton community dynamics.


Three hypotheses related to food web dynamics and stratification have been tested


      I) Decreasing mixing depth of a water column will favor phytoflagellates over diatoms and thereby change phytoplankton communities


      II) Decreasing mixing depth therefore decouple prevalent phytoplankton – zooplankton dynamics by changing food quantity and quality (biochemical composition) for different zooplankton groups.


      III) Decreasing mixing depth will favor jellyfish growth.

The Bay of Hopavågen - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Picture 2 - The Bay of Hopavågen - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and
Patrick Fink

The experiment took place at the “HYDRLAB Sletvik Field Station” (Norway). For this purpose, 18 enclosures were established with a three times replicated gradient of mixing depth of 2, 4, 6, 8, 10 and 12 m (Pictures 3 and 4). Each enclosure (∅ 0.95 m) was regularly mixed (twice a day) with short pulses (5 min) of compressed air. We have analyzed the physical and chemical environment and the composition of the plankton community in the mixed layer of all 18 mesocosms for 3 weeks. For more detailed insights into food web dynamics, we have additionally analyzed biochemical compounds and stable isotope patterns of carbon and nitrogen within biomass of phytoplankton and zooplankton.

Picture 3 : Mesocosm bags before deployment © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Picture 3 - Mesocosm bags before deployment © M. Stockenreiter, Luna Benitez Requena, Sabine
Schultes and Patrick Fink
Picture 4 : Mesocosm bags after deployment © M. M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Picture 4 - Mesocosm bags after deployment © M. M. Stockenreiter, Luna Benitez Requena, Sabine
Schultes and Patrick Fink

A tube-sampler was used to collect a volume of about 5 liters of seawater in each measocosm. Water samples were then transfered in large cans and brought back to the laboratory for subsequent processing and analyses (Pictures 5).

Pictures 5 : Tube sampler (left) and filtration units (right) used to collect and process samples to further study the dynamics of planktonic organisms (phytopankton, bacteria). © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Pictures 5 - Tube sampler (left) and filtration units (right) used to collect and process samples to
further study the dynamics of planktonic organisms (phytopankton, bacteria). © M. Stockenreiter, Luna
Benitez Requena, Sabine Schultes and Patrick Fink

Population dynamics of different groups of planktonic organisms were studied, with a focus on phytoplankton, zooplankton, gelatinous zooplankton, especially appendicularia, ctenophores, and hydromedusae (Pictures 6).

Pictures 6 : Examples of gelatinous zooplankton (Beroe sp. and Bolinopsis sp.) collected during the mesocosm experiment - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Pictures 6 - Examples of gelatinous zooplankton (Beroe sp. and Bolinopsis sp.) collected during the
mesocosm experiment - © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink

The mesocosm experiment was overall successful, and we’re able to sample all parameters. The experiment was stopped a few days earlier than expected because of a period of strong winds over the Bay of Hopavågen. A 12 m deep mesocosm was lost, and it was decided to perform the last sampling on 10/09/2017, before further damage on the mesocosms (Picture 7).

Picture 7 : The mesocosm infrastructure was brought back to the shore at the end of the experiment (September 2017) © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink
Picture 7 - The mesocosm infrastructure was brought back to the shore at the end of the experiment
(September 2017) © M. Stockenreiter, Luna Benitez Requena, Sabine Schultes and Patrick Fink

 

Back