Task 2 Microscopy of preserved plankton samples

Background: During the MicroPolar cruises net-hauls and concentrated water samples have been collected and preserved in formalin, glutaraldehyde and Lugol’s solution. Size fractioned water samples in the size groups >200, 200-50, 50-10, 10-3, 3-0.8 µm from 4 depths (1, chl max, 500 and 1000 m) per station have been preserved as above for microscopy. Water samples with pico- and nanoplankton were concentrated 100x by tangential flow filtration (Shi et al. 2009) and these were fixed, but cells can stay alive for weeks.

Aim: Analyse preserved net hauls and concentrated water samples by LM and EM and precisely identify and describe taxa. Obtain distribution information from historic samples up to 100 years old.

Planned work: All samples from MicroPolar will be processed and examined at UiO EM-lab as below.

Diatoms. Net-hauls and ice-samples preserved in formalin and Lugol’s solution will be examined in LM and the formalin preserved samples will be further processed using a cleaning method to remove organic material (Hasle 1978), mounted on stubs and analyzed in SEM. For a global change perspective, comparisons of the present diversity will be made with historic samples collected in the Arctic, some of them being more than 100 years old including samples from the Fram expedition lead by Nansen and Maud expedition lead by Amundsen. This is possible with diatoms for which historic specimens are archived at the Natural History Museum, University of Oslo and the Natural History Museum of Denmark. Most of the historic specimens are available as cleaned frustule preparation (the cell wall of silica, the organic material is dissolved) and as a consequence all DNA is already degraded and only microscopy investigations are possible.

Dinoflagellates and other flagellates. The glutaraldehyde preserved net samples and concentrated size fractions of micro- to picoplankton collected in MicroPolar will be examined in LM and further processed for EM. The net samples will be post fixed in osmium tetroxide, dehydrated in an ethanol series and critical point dried before they are mounted on stubs, metalized with platinum and analyzed in SEM. The concentrated size fractions will be prepared for SEM, and whole-mounts and thin sections for TEM according to Eikrem & Moestrup (1998).