On Deck: With completion of the tow, the nets were immediately washed with seawater as they were pulled on deck and the plankton still in the nets carefully washed into the cod-end with a seawater hose. The cod-ends were placed in buckets with ice packs to cool the samples and moved expeditiously into the walk-in cold room to await analysis.
Specimen removal: All sample handling except microscopic examination was done in the cold room. The contents of codend bucket was first poured into a tray for a photograph of the entire sample. Then, followed picking and removal of large individuals of 1) gelatinous forms, 2) fish, and 3) macrozooplankton/nekton into cold seawater while a recorder wrote notes on the gross composition of the sample. The specimens removed were placed in numbered jars, shell vials, or dishes and the recorder wrote down all specimen information on the data sheets provided. The removed specimens were subject to a variety of procedures including further identification, dissection, preservation (in alcohol, frozen nitrogen, or formalin as appropriate), or taken for photographic imaging prior to preservation.
Sample splitting and preservation: Splitting was done using a box splitter. The first half was put into 95% pure (undenatured) ethanol. The second half was split again into 1/4 live and 1/4 formalin with buffer (sodium borate) added. The 1/4 live portion was kept in the cold room (time noted). Photos were taken of selected live animals and scientists removed and identified some zooplankton from the live split for genetic barcoding. Once done, the rest of the live sample was preserved in 4% buffered formalin (time noted). Twenty-four hours later, the ethanol was changed and the lid marked to show that this was done. Samples in the 1/4 ethanol were stored in a refrigerated storage area on the ship and later off-loaded at AWI for further examination and archiving. Live and formalin splits were transported to WHOI for further examination and storage.
For information the genetic barcoding protocol, see http://www.cmarz.org/barcode/protocols/protocols.html or email Ann Bucklin, UConn, ann.bucklin-at-uconn.edu.
Euphausiids: Some euphausiids were examined from all three fractions: formalin, ethanol, and live. The formalin split was not used for DNA analysis, so early in the cruise they provided a good source of euphausiids that could be examined at length in order to establish the species present. Once we became familiar with the species, we mainly sorted from the ethanol samples. These were most useful for submission to the on-board DNA barcoding effort because the live fractions could be looked at only briefly in order to keep their genetic material intact. Many of the specimens were photographed using the dissecting microscope and camera equipment provided by Cheryl Clark-Hopcroft.
Euphausiids were identified from the first four MOCNESS stations with a total of 172 euphausiid specimens representing 23 species, more than 1/4 of all known species worldwide. Most of the euphausiids were found in the 1-m2 MOCNESS samples, which collected in the top 1,000 m. Only three species were collected in the 10-m2 MOCNESS and they were found in the shallowest net (1,000- 2,000 m) although not all nets were examined from the tows. Photographs of the specimens will be used as identification checks, for the web photo gallery and as material for the CMarZ species pages (see www.cmarz.org).
Measurements of eye and carapace lengths are the primary method of distinguishing N. atlantica from N. microps, two very similar species with overlapping distributions. This relationship was originally established using formalin preserved specimens and may not hold for animals in 95 % ethanol, in which they shrink significantly. The photos of Nematoscelis atlantica (Fig. 3.6.1) were used to record eye and carapace lengths of the ethanol specimens and will be used to compare with formalin data. The genetic analysis will be essential for validating this method of identification." (from Polarstern ANT/24-1 Cruise Report)
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