An(other) Unexpected Zooplankton Survey

Rhian Taylor

After what feels like a whistle-stop trip back to the UK (but was in fact just shy of 4 months), I arrived back in the Falkland Islands in mid-October to continue my collecting and identifying the zooplankton community here in the Falklands. Theoretically, I arrived just in time to be here for the spring phytoplankton bloom and the corresponding peak in zooplankton biomass. I say theoretically because so far, the two boat days I’ve been on (beginning of both November and December) there’s been a lot of zooplankton biomass (mainly crustacean larvae), but no phytoplankton. Both times we’ve gone out anticipating it being a very long day, with lots of rinsing of the net required (due to the fine mesh getting clogged up by all the phytoplankton), but the nets and sieves have been draining easily. That is something of a relief, mainly because after some technical difficulties, our on-board hose stopped working, and we’ve had to be washing down the nets with buckets of seawater (collected from other the side of the boat, as required) – fine when you’re just washing a few animals down, I don’t even want to imagine how long that would have taken had the nets been full of phytoplankton!! With the nets taking far less time than expected to filter, we were able to stop for a proper lunch break between the second and third station for the first time ever! Which of course meant that the next station started with a sample completely full of copepods. We thought we knew what to anticipate between one station and the next, but we can never assume anything!

The timing of my return was carefully decided so that I would be in the Falklands to work on another key component of my PhD, looking at the ichthyoplankton (the fancy word for ‘fish larvae’) when they’re still fresh to make a note of key identifiable features. We were a bit surprised when there were around 1000 fish larvae in the September survey (while I was still in Aberdeen). Still, we did seem to plan alright for the peak in fish larvae, with over 2000 being collected in November, which I was able to go through. It seems that the main thing we have discovered from the seasonal zooplankton surveys is that we never have any idea what to expect in the next collection! As all of the fish have to be looked at fresh, while still on the boat, we have to take these larvae out of the rest of the sample, which has led to the creation of a new game we’re calling “Tweezer Ninja”, where the aim is to try and pick out as many fish as possible using the tweezers (the title is quite self-explanatory). Somehow, this has turned very competitive, though as none of us have kept track of our scores, it’s hard to work out who the winner of the game is!
Image left: Bongo nets following a hail storm
Images above: southern fulmar keeping watch over our work & fish larvae
My time in the first year of my PhD has been fairly evenly split between being here in the Falklands and being in Aberdeen, and there are specific tasks I have that can only be done in one place or the other. While I’m here in the Falklands, I spend a lot of time going through all of my zooplankton samples by looking at them under a microscope, sorting the animals into “morphospecies” (different groups based on their physical similarities), then counting and weighing all these individual groups. From this work, I am able to identify some of these organisms to a genus or species level using a variety of taxonomic keys. However, since there are very few studies trying to identify all the zooplankton species here, the work I do in Aberdeen can help me identify the species in a different way. 
Image above: working on DNA extractions in Aberdeen
Whilst I was in Scotland, I spent a lot of time in the lab taking tissue samples of the different zooplankton species, extracting the DNA from these, amplifying the DNA using PCR and finally sending the purified product to a laboratory in Germany where they would fire a laser at my samples to read the base pairs of the DNA. This process is known as DNA barcoding, and by using this, I am able to distinguish between different species in my samples that superficially look very similar.

By combining these two identifying techniques, not only am I able to identify more and more of the species in my samples, but I can also use one technique to fill a gap in the other. An example of this is for the crustaceans (e.g. crabs, prawns and lobsters) found here. Using taxonomic keys, I have identified the larval stages of a number of different crab species. Most of these crab species have not been DNA barcoded before, which means that currently, if I tried to find a match for these species in the DNA database, I would not come up with the correct answer. In fact, when I tried to do this, the database tried to find the closest related species to my sample… and came up with crab species only found in Hawaii and Easter Island. Safe to say, those are not the species that we have here! Because I have been able to identify these species based on their physical characteristics, I can then add the barcodes I’ve generated to the DNA database, and that means if anyone else has a sample from the same species, they would be able to find a match for their sample in the database.
I’m very happy to be back here in the Falklands and going out on the boat to get the samples! It’s great to be able to be back in the lab going through the samples again, and actually knowing what far more of the species are than when I left, thanks to the work in Aberdeen. As we’ve had a couple of volunteers in SAERI for work experience week, I’ve been putting together a photo ID guide to allow for quick species identification – it’s a very nice way of being able to visualise what work I’ve done, and what I still need to do. I have a nick name for each of the morphospecies I find in my samples, but at some point I am going to have to have a more formal name for these!
Image above: Samples after a storm - kelp confetti and krill!
Image left: Krill clearing showing photophores
This project is hosted by the University of Aberdeen and SAERI. Collaborators and sponsors include Fortuna LTD, Darwin Plus, Shallow Marine Surveys Group, Falkland Island Fisheries and the Environmental Studies Budget (Falkland Islands Government). Rhian’s PhD supervisors include Dr Jesse van der Grient and Dr Paul Brickle at SAERI and Professor Stuart Piertney and Dr Alex Douglas at the University of Aberdeen.
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