Fish Patterns in the Seasonal Seascape

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Freezing waters surrounded by picturesque scenery on a cold (-15°c) winters day in the Gullmarn Fjord, western Sweden. If you look closely in the water, a curious common seal keeps watch.

Tom Staveley is a Marine spatial ecology & PhD candidate at DEEP Stockholm University and he is currently putting the finishing touches on his thesis. Both of us are living the invandrare life in Sweden at the moment so I got a chance to catch up with him recently and managed to drag him away from the thesis for long enough to give us a run down (below) on some of the research he has been working on.

Fish Patterns in the Seasonal Seascape

Being a marine ecologist in Scandinavia certainly has its advantages: long summer days to do seemingly endless fieldwork, stunning surroundings and surprisingly lush underwater habitats (yes, I’m talking mainly about seagrass but we’ll get to that later). Even in the heart of winter a sublimely frozen wonderland of crisp air, still bays and snow-covered land- and seascapes never ceases to amaze. For the past few years, I have been exploring the coastal waters of western Sweden in the Skagerrak/North Sea focusing my research on seascape ecology – a relatively new branch of marine science focusing on broad-scale patterns and processes in the seas and oceans.

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When it’s cold enough (and not so much wind) the more sheltered parts of the sea freeze, and with surprising speed. In just a couple of days we couldn’t reach our sites (Ed: Somewhat ironically Sweden is currently undergoing its hottest July on record and at the time of posting we are all cooking in 32 degrees+ temps!)

To kick-start this project, our team (consisting of supervisor Martin Gullström, fellow PhD candidate Diana Perry and myself, as well as many hardworking assistants) started looking at large circular areas of shallow-water environments (termed seascapes) all with a seagrass meadow in the middle. The main aim was to see how the differences in surrounding underwater patches of habitats were affecting seagrass fish assemblages in different seasons. In these seas, we are talking about habitats dominated by for example seagrass, macroalgae (seaweed), rock and sand. What we discovered was that the less ‘complex’ a seascape was, e.g. less patches, habitat types and edge boundaries, the better this was for many parts of the fish assemblage such as juveniles, particularly in the summer. This was a classic seascape approach with the use of spatial pattern metrics (tools developed in the terrestrial counterpart landscape ecology) to assess habitat and patch patterns in the seascape. You can read more in our article open access here.

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Although we have no seahorses in Swedish waters, many of their relatives like this Greater pipefish are common in the shallows. Here, this individual was moving gracefully through the seagrass at the edge of a meadow.

Like in other parts of the world, seagrass meadows in these waters sustain relatively high numbers of fish, and can be particularly important as nursery habitats for juvenile fish, like cod. The dominant seagrass species here in western Sweden is eelgrass, which can be found down to around 6-7 metres in sheltered bays and inlets and form dense meadows. Even though these habitats are very important throughout the world’s shallow seas they are in decline and lack appropriate protection for their conservation (including in Sweden). Just to deviate a little…if you see a seagrass meadow you can report it at seagrassspotter.org, which presents a fantastic citizen science project designed to help in tracking seagrass around the globe. It might come as a surprise, but we don’t even know exactly where all the seagrass meadows are in Swedish waters, let alone how much there is, and their quality. This basic information is fundamental; particularly as numerous fish species (many of commercial interest) are reliant on these habitats.

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The calm after the storm: Hard to imagine but just a few minutes earlier we were collecting fish during a heavy downpour. After we released the fish and got the net packed away (front right) we could enjoy a well-deserved ‘fika’ (that’s Swedish for a cup of coffee/tea, chat & perhaps a biscuit 🙂 ).

Let us get back to fish and seascapes; throughout this project, we have used multiple methods and tools to be able to understand patterns and processes at various scales through the temperate seascape. For instance, we undertook fish surveys though beach seine and underwater stereo video cameras, habitat mapping using drop video, and tagging and tracking fish through biotelemetry

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Above: Tom & Diana using the drop video camera to find out what underwater habitats are present. These methods can be used to map underwater habitats that aren’t always visible from the surface, such as this eelgrass meadow.  Below: These are two common ways to see what kinds of fish are living in seagrass meadows. On the right, a beach seine net is being hauled over a patch of seagrass to catch and identify fish. The underwater cameras on the left are a non-destructive alternative to watch fish in their natural environment.

My colleague Diana Perry has tirelessly watched hour after hour of underwater videos, locating, identifying and measuring fish from seagrass meadows, macroalgal belts and unvegetated habitats. From these observations and by linking fish data with large-scale geographic variables, we have found that some fish groups are influenced by not only near-shore habitats and patches (as mentioned above) but also the offshore environment, adding another dimension to our project. Also, these non-intrusive camera methods allowed us to investigate differences and similarities in fish communities between habitats. Interestingly, here we found that seagrass- and macroalgal habitats did not differ vastly in composition of fish species or abundance, but instead the 3D structure of these habitats is perhaps the most important aspect in contrast to the more flat, unvegetated sandy bottoms. Find out more open access here.

Information at the broad seascape level is important to understand how and when fish are using particular habitats so actions can be taken at a management level and hopefully aid in the well-needed conservation of marine ecosystems.

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Typical archipelago land/seascape on the west coast of Sweden. Rocky shores dominate creating a surface for many types of seaweed. Much of the shallow seafloor is soft bottom, ideal for seagrass to grow in the sheltered bays and coves.

Currently, my time splashing around in seascapes has pretty much come to an end (for now), but instead I find myself office bound back in the capital, Stockholm, where I am on the home stretch towards completing my PhD as well as analysing data from an acoustic telemetry experiment. Here, to further assess connectivity of fish throughout the seascape we tagged 48 juvenile Atlantic cod to try to understand more about their movements in shallow-water coastal areas. I’ll have to save this for another time though 🙂

For those of you who want to dive deeper into the world of seascapes, I can recommend the new book ‘Seascape Ecology’ edited by Simon Pittman, 2018.

Please feel free to contact me:

Tom Staveley

PhD candidate, Department of Ecology, Environment & Plant Sciences (DEEP), Stockholm University, Sweden. tom.staveley@su.se. Twitter: @tabstaveley

Bonus: Watch fish live! Underwater camera in one of the seagrass meadows where we work. (Not sure if you can somehow display this livefeed on the blog? or add it in as a cool link?)

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