Dana

Serra Örey and Jens Ulleweit report:

Looking for eggs with 1 mm diameter in a vast ocean area is almost like looking for a needle in the hay.

Our plankton sampler (Nackthai) has a net with 280 µm mesh size (meaning that particles bigger than one quarter of a millimetre like fish eggs will be caught by the net). It is deployed from the side of the ship, veered and towed behind slowly. If we send it down to 200 m, we can filter approximately 250 cubic meter of sea water (knowing the volume, we can later calculate how many eggs per single volume can be found). When the gear is on board again, scientists wash the net, concentrate the sample in a collection bucket and change it with a clean one for the next haul. The ship crew manages the heavy equipment on deck in all sort of weather conditions. Later in the laboratory, the sample is fixed with formaldehyde solution in a bottle to be analyzed later by sorting out the fish eggs and counting them.

One of the biggest parts of biological sciences and fisheries is counting. In fisheries science, fish and plankton are spread over three dimensions. Moreover, distances on sea are great. That’s why we have to pick stations (certain GPS locations where we can conduct the sampling) over a transect to cover a bigger area. During the whole expedition, we are responsible of an area approximately 160,000 km² within the Northern Bay of Biscay, the Celtic Sea and in waters west of Ireland, which we have to cover twice.

The mackerel survey is coordinated by the ICES (International Council for the Exploration of the Seas). If you are interested in the ICES work and how the stock size of mackerel is currently assessed, here comes the link: https://www.ices.dk/sites/pub/Publication%20Reports/Advice/2019/Special_Requests/no.2019.09.pdf.

As I write this post, we are completing our first week on board and our ship has already been to 30 different stations. Working 24 hours with rotating crew shifts, we are aiming to complete up to 180 stations during the whole expedition.

Marsha Dechant, Tarik Mais and Vivien Wiedbrauk report:

Moin, moin dear landlubbers!

Here is a small contribution from three students of the Hochschule Bremerhaven! We participate in the cruise as student assistants and briefly describe our impressions:

Onboard of research vessel Dana, each of us has a single room – which is in our opinion very pleasant and a plus. Each room has a TV, desk, music system, storage space, private bathroom and enough space. There were a couple of things to learn for new seafarers like us. Like how adventurous showering can be or which angle you have to take towards the ship for better sleep. Nevertheless, we got used to being onboard relatively quickly.

We all eat together, sailors, officers and scientists, in the cozy wood-paneled mess room. There is a buffet three times a day, with two additional coffee breaks – just to make sure that no one starves. The food is comparable to that of a fine self-service restaurant, high quality products with a large selection. Moreover, our friendly cook leaves no vegetarian behind. Our favorite so far has been the roast beef burger (with a veggie alternative!).

Daily routine is variable for each one of us, as we help on wherever needed along the sampling procedures. We fill protocols, work outside on deck to get the sample, transfer it to the laboratory for sorting and counting the eggs. Sometimes this can lead to an adrenaline rush when the bucket with the precious sample slips over the deck in heavy seas. The waves of the past week have also bounced us around the room, working in the lab. Moreover, you have to make sure that everything is always sea-safe, using for example anti-slip mats. And all the rolling made it clear what everyone meant with "always have a hand for the ship".

When the sample is finally processed, we may easily end up with counting 6,000 eggs for one station. If there is still time, we also determine the other organisms in the sample. We are supported by our experienced colleagues and have a chance to apply our university knowledge.

During leisure, a well-equipped gym is regularly visited. When the weather is nice you can relax with a book on deck or look out for birds, dolphins or other marine mammals. Observing gannets diving like arrows into the waves is always impressive. There are also board games, a game console and an enormous DVD collection. Wi-Fi allows us to have contact to family and friends from time to time. Moreover, the atmosphere onboard is always friendly and we also find the working atmosphere very positive. The Danish crew is also in a good mood all the time and very helpful, so that enjoying work is easy!

Ahoy and see you next time!
Marsha, Tarik & Vivien

Serra Örey reports:

On our 157th plankton sample, something extraordinary happened, second time. While pouring the fresh plankton out of the collecting bucket, I announce the exciting news to my shift mates: It is a GLOWING SAMPLE again! This time we are prepared to spot who is responsible.

When we push the plankton soup with a little spoon, blue sparks appear. First time we got a sample like this, all of us speculated that it must be the usual suspect: Noctiluca scintillans, a plankton from the family of dinoflagellates that blooms (proliferates to great numbers in suitable food and temperature conditions). Those “blue tides” can be visible even from space as waves create the bioluminescence by mechanical distribution of millions of those one celled organism.

However, in our second catch we want to find exactly, who is responsible. Lights get dimmed in the lab and everybody is trying to pick the glowing bits from the soup of plankton and looking through microscope. Vivien has a glowing arrow worm hanging in her forceps, Tarik swears that he saw a copepod’s antenna that was glowing. I spot the blue blinks of the light organs of a krill! We are overwhelmed, as the enzymatic event that produces the chemical blue light decays in a blink of a second. We take a good video of our shiny blue sieve, but taking pictures under microscope is harder. We give up before making a decision, as time is short while working with fresh plankton samples. We must quickly preserve it in formalin. If we wait too long, our important fish eggs may get bad (or even are eaten by other specimen!).

Later in the lab we start reading literature about bioluminescence in ocean. Fortunately, many articles are online these days, so that we always have our library at hand even far away on a research ship. We realize that we could all have been right! Of all the families of organisms living in the sea, one or two species are known to produce light.

Planktons are fascinating drifters of ocean – eggs, small jelly organisms, small crustaceans like copepods and numerous other organisms. We are lucky to see these wonders of ocean first hand.