26 June 2023

By Eleonora Puccinelli

We are nearly at the end of the ACTNOW cruise, an intense 10 days where we worked around the clock to provide data for this exciting multidisciplinary programme. We looked across the entire food chain, from small plankton in the water column passing through fish and benthos up to birds, trying to understand what the link among all of them is.

In the cruise I mostly focused in getting a better understanding of the trophic links between primary producers in the ocean (phytoplankton) and small consumers that feed on them (zooplankton), and I did that by looking at the lipid and in the specific omega-3 composition of these groups. Why should we even care among all of this? Omega-3 are essential components that we all need to have to function well, and in the ocean the main producers is phytoplankton (right, those small little guys!). Consumers including zooplankton, fish or even humans, cannot produce them in sufficient quantity and we all must acquired them via our diet. We also know that some phytoplankton groups make specific omega-3, which remain untouched in the food chain, which can thus be used as “biomarker”. This means that if a consumes has a specific omega-3, we can track what it ate in the past and provide a better understanding of his foraging strategy. Such a powerful tool!

Left: Eleonora and Sophie collecting water from a CTD cast. Right: CTD coming back on board.

While I will be able to generate final data on omega-3 after I analysed my samples in the specialized labs at NIOZ, samples have been collected daily during the cruise making use of the CTD and its rosette to collect water from several depths in the water column which I then filtered. I have been doing this with the incredible help of Sophie, and fun fact, the CTD teem filtered approximately between 85 and 130 L of water per station, coming approximately to 2000 L of water filtered in the entire cruise.. that sounds like a lot of filtration!

Lots of first for me on this cruise. First time at sea since at NIOZ, first time sailing in the North Sea (and North Hemisphere) and first time on a cruise as PI. A cruise that definitely I will not forget.

I will leave you with a photo of the incredible team from crew to scientists that was involved in the ACTNOW cruise and that made this trip a real success!

Left: ACTNOW cruise photo. Right: Filtration set-up.

22 June 2023 

By Loran Kleine Schaars

Life of the nightcrew

A first update by your favorite nightcrew. Work on the Pelagia continues 24 hours a day this trip, and under beloved supervising of Rob Witbaard especially the dredge team is sampling in the night. In that way we can get the most out of this trip but way more important, nighttime is the moment we can sample our target species, the sandeels.  Therefore our rhythm also changed and I will take you through our daily routine. Besides Rob the team consist of Bram Parmentier (NIOZ, PhD sandeel project), Eva Immler (NIOZ, research assistant sandeel project) Elena Couce (Cefas, taking care of stomach content of fish), Sophie Brasseur (WMR, nothing she can’t do) and myself, taking care of the taxonomic identifications of all caught macrobenthos. We are very very well supported by the crew of the Pelagia who makes sure we can do our work nice and safely. Without them this would not be possible.

Our day starts around 22:00 when we wake up and prepare ourselves for the night. It’s also just in time to enjoy the beautiful sunsets over here which is around 22:45 and with some luck see the last whales of the day. Around 23:00 twilight starts and so does our working day. The triple -d dredge is waking up and is launched for the first time in the night. How that exactly works can be found here à (21) NIOZ Triple D Operations clip - YouTube

When back on board it’s always a surprise how the catches look like. Doggerbank is well know for area’s with gravel/stones, but also (fine) sand, mud and clay catches occur. This also means that the animals that are living here are quite diverse. When the net is emptied the catch is described and photographed and after that it will be sorted on the sorting table. In first case we focus on the fishes so they are out of the sample and don’t need to suffer to long. They will be euthanized as quick as possible. After that, and if there is time enough, we also sort the macrobenthos. Everything will be identified up to specie (if possible) and after that is measured and weighted. If no time we store the samples in our cooling container to process them the next day. This routine goes on till around 5 in the morning when daylight starts to be back again. Usually that means around 6-10 samples a night depending mostly on the sailing time between the points.

The whole idea is that sandeels dig them self into the sand during nighttime and therefore can be caught by the dredge. During the day they are probably foraging in the water column and a quantitative sampling is not possible. Because the dredge is catching exactly 10 m2 every time we now know the density of sandeels living on that area. 

Between 05:00 and 06:00 it’s time for us to stop working again, sometimes just in time to quickly report to Kees, our expedition leader. Kees and Mardik wake up around that time to start their shift, watching out for birds and sea mammals. For us it’s time to find our cabins and get some rest. That will be up to 12:30 when we have breakfast with the rest of the crew. Their lunch will be our breakfast, usually not a problem but on a ship you have your “warm meal” during lunch. that means we are waking up with hotchpotch and meatballs, or steak and french fries.  After breakfast we go out on deck again to process the remaining samples that we couldn’t finish in the night. With some luck we finish in a couple of hours and we can assist the rest of the team or enjoy some free time. At 18:00 we have lunch (and the rest of the crew dinner) and after that it’s time to get a couple of hours sleep again. Till 22:00 when it starts all over again…   

21 June 2023

By Pieter Hovenkamp

Going from big to small, today’s story is about the work on plankton that we are doing this expedition. But whereas most people can imagine how a seabird or seal looks like, the term plankton deserves a bit of explanation first. Plankton comes from a Greek word meaning ‘to wander, to drift’ and it refers to all pelagic organisms in the sea that are unable to swim against currents - pelagic refers to the area between the sea floor and surface. Within the plankton, we distinguish between phytoplankton, or algae, that do photosynthesis, and zooplankton, which are the animal-like groups within the plankton that feed on other plankton. More on algae later, my work this cruise is on zooplankton.

Zooplankton is hugely diverse group of animals, ranging from copepods - a small crustacean that is highly abundant throughout the world’s ocean - larvae of many bottom-dwelling species such as worms, shells and sea stars as well as fish larvae and even various types of jellyfish. They play a vital role in the food web, as they are the link between algae and the larger organisms such as fish, sea birds and mammals. This is also what we aim to explore this expedition: how are the patterns that we observe in zooplankton linked to the observations of phytoplankton and larger animals that my colleagues are doing simultaneously?

Left: The CPICS camera mounted at the bottom of the CTD rosette. Right: The instrument frame carrying the ISIIS, and various other sensors, before it is lowered in the water. Below the frame is a fin that stabilizes the frame as it is towed through water

Although zooplankton is typically collected using a net with a very fine mesh size, using this expedition we are working with a different technique as well: we deploy underwater microscopes that take photos of zooplankton directly in the sea. One advantage of this technique is that we know exactly at which horizontal and vertical position a certain species is recorded. This then makes it possible to count species along a whole transect or depth profile, and if we then link these observations to seawater conditions such as temperature, salinity and amount of dissolved oxygen that we record at the same time, we can find very detailed patterns in zooplankton communities and their response to water conditions.

So far, we have collected 65.301 images with CPICS and about 115.000 images with ISIIS, and each ISIIS images typically contains many different organisms per image. These numbers will increase vastly over the next days. With such numbers, it will be impossible to manually check all the images we collect, so when we are back home, we will work with machine learning methods to have our plankton images identified. So although a glimpse at the data already shows that there are large differences in the zooplankton communities between the various stations we have sampled so far, getting more insight into what is happening on the Doggerbank will take a bit more time after this expedition is finished.

Left: Some images taken with the CPICS camera this cruise. On the images are (i) a copepod with eggs, (ii) sea sparkle (Noctiluca scintillans), and larva of a (iii) gastropod (snail) (iv) bristle worm (v) fish (vi) sea urchin (vii) sea star. Can you guess what is what?

Right: Some images taken with the ISIIS camera this cruise. The top image is planktonic tunicate that forms a mucous web to capture food particles (like a spider’s web). This is impossible to observe with a net, since the web will get destroyed very easily. The middle image is a copepod and the bottom one a small jellyfish.

Friday 16 June - Sunday 18 June 2023

By Sophie Brasseur

So, during the 10 days that this cruise will last, large parts of the western Doggers Bank are covered, with scientists on board observing and counting seabirds, seals and whales while logging their (foraging) behaviour and interactions. Fish abundance should be assessed simultaneously using an acoustic fish finder, while zooplankton communities and even primary productivity (the growth of phytoplankton) are derived from underwater observations using an advance photo and video set-up that is towed through the water. At night, when sandeels settle in preferred sands, the ship deploys the Triple-D to take samples from the seafloor, in which the abundance of sandeels is assessed while the benthic community is subsampled and analysed. Also, stomach contents of capture fish is inspected to see what they feed on and eDNA (environmental DNA) is subtracted from water samples to trace the species composition of the fish fauna in different water layers. To realise all this, we are following a 24 hour schedule, making observations and sampling during the day pinpointing areas that might be of interest to dredge for when we sail the same track back during the night. Thanks to the great crew on board of the Pelagia, making this possible and supporting us, they too have to work these shifts!

White beaked dolphins

So far the perhaps slightly boring background. Now what happened in truth. Having left on Friday the 16th with perfect weather and wind, we realised in the evening that we would reach our fist sampling station early on the 17th instead of at the end of the day. In a light panic we all had to setup our different laboratories and get the gear ready. It always takes some time to get everything in order for the complicated measurements and sample collection on bord a ship some of us do not know well. Will the method thought-up on land actually work at sea? Do the instruments record at sea, what we thought they would? Where can I ideally put my gear to obtain the best results? Is all the material I need on board? Despite all this, the first day went very well; on the first expected area of importance (based on only very few seal tracks that we had received beforehand) we seemed to hit bulls eye: several minke whales were the first sign that we had arrived at an important feeding ground. What happened next was even more significant: over 200 grey seals, together with a few dozen White-beaked dolphins were seen hunting in packs, jointly and separately, in a very small and distinct area while numerous Black-legged Kittiwakes but remarkably few other seabirds remained fully inactive. The actively hunting seals and dolphins seemed to work (feed) mostly at depth, thereby not generating anything of interest for the seabird community, which is important information that could help interpret what was going on, and what prey would likely be targeted. The almost complete absence of (deep-diving!) auks was most striking, and the hypothesis was therefore that the seals, dolphins and the whales were targeting something like demersal gadoids rather than small pelagics.

Left: Eleonora and Loran at the incubators. Right: Northern Gannet

Samples taken at night within the same area failed to produce sandeels (or very few), which seemed to be in line with what was observed at daytime and what we deduced from the combination of active species within the area. The hotspot in terms of seal abundance was quite a bit more important than what was derived from the tracking data, just because only rather few of the actually tracked seals had utilised the area just before the cruise: enough to make it an area of interest beforehand, but too few tracks to be prepared for what actually happened in the area: a spectacular feeding bonanza with grey seals hunting side by side in dense packs as wolves.

On the next day, the 18th, we more or less are starting to get the hang of it and most studies seem to be going well. Quite the opposite happened on this day: a very rich area according to seal tracking data, turned out to be a fairly poor area from visual observations (yes, seals, but few and quite inactive during our visit), while sea seafloor samples turned out to be rich, particularly in terms of sandeels! Seabirds were, again, remarkable absent, suggesting that their hotspots were not connected with seals, at least not here. Interesting, perhaps even more interesting than a positive link between sandeel abundance and foraging megafauna: now we learned …. It isn’t that simple. The following days are bound to learn us more!

Generally, seals capture fish close to the seafloor, so hopefully while the dredge may give info mostly on sandeels, the eDNA that is sampled may shed light on other species within the same areas. eDNA allows us to trace species based on minute amounts of DNA the organisms left behind in the environment. Twice a day, at strategic points on our daily tracks we will be sampling the water column at the surface, mid depth and bottom.

Survey tracks (thick red, not the biq square) are: departure from Marsdiep (16 June), across the Dogger plus the first scheduled transect (17 June) and the third scheduled transect plus a return journey to facilitate the zooplankton frame (18 June)

More news will follow the coming days, when the various teams get better and better in timing and gear handling: Pieter and Anton at the “zooplankton frame”, Eleonora and Sophie working on the CTD, eDNA (water samples) and zooplankton, Rob, Loran, Elena, Eva, and Bram mostly in charge (with help from the others when possible) of the Triple-D and “sandeels sorting”, and Mardik an Kees on the monkey islands to visually examine the area and megafauna abundances that might pin-point areas of interest.

Monday 19 June 2023

By Markdik Leopold

Where have all the seabirds gone?

We all know it, or should know it: one year of data does not tell us much. In nature, there is often considerable year to year variation, in any parameter you can measure. Evenso, when Kees asked me to join him on this 10 day cruise to the northwestern slopes of the Dogger Bank in the Central North Sea, this was a no-brainer. For seabirds, seals and cetaceans, aka the ‘charismatic megafauna’, this place is known as one of the best places in the North Sea. An area of internal waves hitting the sloping sea floor, of fronts, of high productivity and situated within reach of major UK seabird colonies. And on top of all of this, a core area for seals from both the UK and the European Continent, as well as for porpoises, dolphins and even whales.

Grey seals

What could possibly go wrong? Well, for one, last year’s bird flu epidemic killing off possibly half the gannet population in the North Sea. This might explain why we are seeing so few of these majestic birds, in other years communting in long lines between the colony on Bempton Cliffs, and these parts. Not now, we only see occasional single straglers.

Maybe the surviving half of the population does not need to go this far afield, to get away from the competition closer to home? Could be, but this does not explain why we are also seeing much lower-than-expected numbers of common guillemots here, hardly any razorbills, and not even a single puffin or harbour porpoise. Numbers of dolphins and whales are also lower than expected, but at least we are seeing some of those. Only the seals do what was expected of them: turning up in good numbers and hunting in packs for unseen fish. The few birds that we do see here seem somewhat lost. Few are feeding or even actively searching for food. This presumed rich place appears to be largely void of food for most of the piscivores we are targeting during our survey. Something seems to be very ‘wrong here, or at least, very different from the situation in other years, we considered normal.

Right now, after the first three days here, we have no clue of what may have caused this dramatic deviation from the situation we have encountered here in previous years. Bad news? Maybe. But very, very intriguing. Food for thought.