Seasons Change

Rhian Taylor

As the seasons change from summer to winter here in the Falklands, we can see changes in the amount and diversity of zooplankton in the area. This is very exciting to see, as I continue to collect and sort through zooplankton samples collected between September and May. My PhD project aims to improve our understanding both of what zooplankton species we have here in the Falklands, but also how the abundance and distribution of these changes throughout the year.

Due to their importance as a food source for larger predators in the area (including fish, penguins, and whales), understanding the seasonal variation of the zooplankton could also help us understand some of the movements of these organisms. Having been in the Falklands since the beginning of February, I have gone out to collect zooplankton samples for my PhD project several times (and, if the weather clears up, I’m hoping to head out a final time before heading back to Aberdeen later this month).

Image above: selection of zooplankton from May sampling
It has been very interesting to see, even before sorting through the samples under the microscope, that there has been a clear difference in the community structure between collections. In February, I found a wide range of organisms in the samples, with no clear dominant species. These were, coincidentally, probably very good samples to have started with, as I quickly got an idea of the range of different species that I would need to identify.  
In March, the samples were dominated by gelatinous organisms, including comb jellies and a range of jellyfish, with very few of the other organisms present in February. On the next sampling trip (which ended up being in May, due to weather delays), there was a change again, with considerably fewer organisms found at any of the sample sites, and once again no clear dominant species.
Although the boat work is definitely the most exciting part of my work whilst I’m here (I don’t think I’ll get over the variety of wildlife that it’s possible to see here while collecting samples), I have spent a lot of time looking down a microscope and flicking through books and papers trying to identify the zooplankton species. Each set of samples seems to pose a different challenge when sorting under the microscope. October samples are dominated by multiple life stages of the lobster krill zoea, which are very useful to see when trying to identify the life history of this species (though require a lot more concentration to identify than some other samples). To add to the challenge of identifying the lobster krill larvae, these samples also contain the early larval stages for other decapod crustaceans, so it seems that spring is an important time of year for the crabs and lobsters, as well as fishThere is a time pressure to sort through the March samples, as the longer the gelatinous species are out of formalin, the less recognisable they are! My favourites at the moment are the May samples as, due to their low biomass, they are very quick to sort through. I also have found several instances of opportunistic feeding – where some of the larger, predatory organisms take the opportunity to get an easy meal while all of the sample is collected in the cod end of the net – for example, in the May samples, where arrow worms have decided to catch a few copepods (arrow worms are transparent organisms with large teeth and jaw hooks, making them excellent predators within the zooplankton community). Due to their transparent nature, it’s both easy and interesting to see how many they have been able to catch!

Time seems to be going by so quickly now I’m preparing to head back to Aberdeen. Part of that preparation has involved subsampling or decanting my samples into smaller containers, and making sure everything is clearly and accurately labelled, ready for travel north (a process that I will definitely not be doing all in one go next time around). Although I’m sad to be leaving, it will be very interesting to work on the other part of my PhD work, where I use DNA barcoding to identify the species I have collected. Not only will this step help me identify and differentiate between some of the organisms that look very similar, but I will also be able to use this technique to support the work I have already been doing. One way I can do this is with the decapod larvae I mentioned earlier – I will be able to use this technique to confirm my identification of the different larval stages of lobster krill, and also get an idea of how many other species of crustacean krill I have in those samples. I am anticipating that the DNA record of species here won’t have all the zooplankton species I’m finding, but as I have also been identifying species by their physical characteristics, I can use species identified that way to add to this record. I’m really looking forward to seeing how the morphological identification I have been doing pairs with the molecular techniques I will be using.

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.
Image above: Fish larvae in May samples 
Image above: Large hydromedusae from March samples
Image above: grimothea zoeal stages
Image left: Taking a well deserved break between samples
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