So, we are a week in to our mesocosm tank experiments. Yesterday we added 9 Mnemiopsis leidyi (3 into each tank) to our tanks and left 3 without. They have a tendency to sink right to the bottom without any circulation so we had to set up an air lift using compressed air tap in the room. It took some fidgeting with various valves and silicone tubing to get it right, but we finally sorted it so there is equal bubbling in all 6 of the tanks (replication is the law of science).

Sorting out the air pumps into the mesocosm tanks, we need to ensure we have enough air for circulation but not too much to damage the organisms. We also want the same flow rate into each tank.

The other difficulty with this experiment is that we want to check we can see the M. leidyi each day, so we know they are happy and alive. However, they are about 3cm in size, and mostly transparent… so trying to find them in a 30L bucket is a little tricky! Today we managed to find most of them (with some good spotting from my colleague Janice).

Looking down into the tank, can you spot the Mnemiopsis? 

What has been happening in the tanks over the last week? After we added the nutrients (nitrogen, phosphorus and silica) we began to see an increase in algae. Particularly a type of algae known as diatoms. Diatoms have a very rapid growth rate and use the silica to make a case around themselves known as a frustrule. The smallest glass factories in the ocean! They come in a variety of beautiful shapes as you can see below.

Different shapes and forms of the diatom algae (image from https://nualgiaquarium.com/nano-silica-diatoms/)

Along with this, we have also seen incredibly high numbers of small algae (known as “picoeukaryotes”), with up to 90,000 cells per mL of water! However, in the last few days their numbers have dramatically declined, whether this is due to them being eaten by grazers or killed by a viral infection remains to be seen. We have counted both grazers and viruses so can try to correlate these data sets afterward!

We have been collecting (and preserving) a lot of samples from this experiment! For algal biomass, we can look at chlorophyll abundance. Chlorophyll is the pigment algae use to harvest light and turn it into food (photosynthesis) and is green in colour, because this is the only colour in the light spectrum it doesn’t absorb and so reflects back into our eyes (why we see plants as green)!

After filtering 150mL of water we can see the colour from the algae on a filter

We have also been measuring oxygen production and uptake over 24 hours. Photosynthesis produces oxygen, whilst the process of respiration (by bacteria or grazers) consumes it. By incubating samples in the light (the total oxygen production and consumption over 24 hours) and other samples in the dark (just consumption) we can work out the balance between photosynthesis and respiration! As the diatom bloom has been developing we find our system is producing more oxygen than is being consumed, but this could change now that the M. leidyi is in the tank, or as bacteria begin to break down the dying algae.

Oxygen bottles kept in a water bath, the probe is to measure oxygen and temperature from each bottle. Half of these were kept in the dark and half in the light. 

We will keep you updated with more information next week!

Kyle

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Mesocosms are an experimental system, usually within the natural environment, but under controlled conditions. For instance, they can be large tanks, or floating bags within an aquatic environment, for instance at the Espegrend marine field station in Bergen, Norway.

The mesocosms at Esepgrend on a floating platform in the fjord (https://fjordphytoplankton.wordpress.com/2017/05/25/what-do-oceanographers-do-they-study-tiny-organisms/)

They can range in size and also experimental treatments. They have been used to study the impact of CO₂ on marine algae, the influence of increasing temperature and acidity on biological organisms, and also to gain a better understanding of the marine food web.

This understanding of the marine food web, is where my experiment comes in.

As part of my research mobility exchange funded through the World Universities Network, I am in Bergen trying to gain a greater understanding of the marine food web and the flow of nutrients and carbon through the system.

Diagram of the marine food web, showing the different trophic levels from algae to fish (https://oceanbites.org/time-to-rethink-the-role-of-oceans-microbes/)

The experiment we are running is to look at the impact of gelatinous zooplankton (feed on zooplankton and young fish) on the marine food web. For this, we are using small mesocosms (approx. 30L buckets) which have water from a local fjord within them, and a bloom of algae stimulated through the addition of nutrients and additional light.

The tanks set up in the temperature controlled room, light panels provide light on an appropriate day:night cycle length 

Our room is set up with a controlled temperature and light intensity, by controlling these variables we can limit the number of factors which may differ and impact our experiment. Our main objective is to observe the impact  of gelatinous zooplankton. To study this we will have 3 tanks with gelatinous zooplankton and 3 with none added, to act as our “control”. For this experiment, we want to observe, over 2 weeks, what the impact of the ctenophore, Mnemiopsis leidyi, is on marine systems. For 2 weeks we will observe the changes in the abundance of biological organisms (from bacteria to larger grazers), the oxygen consumption and release (through photosynthesis and respiration) and the changing nutrient conditions.

The ctenophore Mnemiopsis leidyii
(https://www.natgeocreative.com/photography/474059)

One reason why we are interested in these results are because gelatinous zooplankton appear to be becoming more abundant in marine systems, we want to know what the impact of them is on the base of the food chain. Do they, as some studies suggest, stimulate algal production through the release of nutrients which are limiting growth? Or, do they reduce phytoplankton biomass by feeding on zooplankton which enhances the population of algal grazers (the smaller micro-zooplankton)?

Stay tuned to find out more!

Kyle

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Members of the Harvey Lab get really excited about phytoplankton and for good reason. Phytoplankton are super important, as they form the base of food webs and govern the transport of nutrients and carbon in the ocean. Phytoplankton populations fluctuate, sometimes growing high in numbers if they receive plenty of sunlight or nutrients. Other times, phytoplankton experience mortality, mainly from hungry grazers called microzooplankton (slightly larger carnivorous plankton) or from infectious viruses. In the Harvey lab, we are especially interested in the balance between phytoplankton life and death and the implications these life dynamics have on the food web. The mesocosms offer us a rare opportunity to assess growth and grazing over time and under different sunlight and nutrient conditions.

Every other day we conduct a phytoplankton grazing experiment. A typical day begins at 0600, rain or shine. After a much-needed slug of gull (Norwegian for gold) coffee, we pack up a small boat with collection bottles and head out to the mesocosm raft for sampling. The sampling is intensive and takes 2 and ½ hours to collect surface water (around 80 liters total) from all 12 mesocosm bags. We did find a local Norwegian radio station that blasts sweet sounds of the 80’s, which helps keep our early morning moral high. The water collected from each mesocosm bag is screened through a 200 µm mesh, which ensures we retain phytoplankton and their dominant microzooplankton grazers.

The Harvey lab heading out to sample on a rare sunny day in Bergen (top). Our boat (bottom) ready for a 6am sampling trip! 

Back on land, the fun truly begins. Some of the water from each mesocosm treatment is mixed with normal filtered seawater, that is free of any plankton. This technique allows us to dilute the natural community (phytoplankton, grazers and viruses) and assumes that phytoplankton growth rates remain unchanged, while mortality rates vary proportional to dilution. Whole and diluted samples from each mesocosm treatment are filled into 1-liter bottles (54 total bottles) and placed in an outside seawater tank for 24 hours. The next day we retrieve bottles and filter them for various parameters. Chief among them is chlorophyll, which is found in all photosynthetic cells (the green color) and is used as a proxy for phytoplankton in the water. By comparing changes in daily chlorophyll in both the whole and diluted samples, we can directly measure phytoplankton growth, grazing and viral lysis rates!

Sean collecting water using a niskin bottle deployed into the mesocosm bags (left). Our on land incubation tank (right). We use a screen on top to mimic the light algae would receive at 1m depth.

There are also important zooplankton grazers larger than 200 µm (called mesozooplankton), which can be small crustaceans or giant jellyfish. We are interested in mesozooplankton, as they can induce what is called a “trophic cascade”. They do this by consuming the microzooplankton grazers of phytoplankton, freeing them from predation pressure and allowing them to rapidly grow. To study the impact of mesozooplankton we use two main methods. One is to not screen the water coming from the mesocosms, this allows us to see how the natural community (including larger grazers) changes over 24 hours. The other is to collect zooplankton using a plankton net, and then carefully pick zooplankton under a microscope and add them to our bottles. This can be quite challenging when the zooplankton are < 1 millimetre in size.

Sean and I using a zooplankton net to collect mesozooplankton from the mesocosm bags

By comparing the results from all our experiments, for micro- and mesozooplankton, and viral mortality we can begin to see how phytoplankton mortality is divided. In the case of mesozooplankton, we can also observe if, and how much of a trophic cascade they may be inducing. These observations will help us to understand the dynamics of phytoplankton populations, and their associated impacts on the marine food web.

Sean Anderson & Kyle Mayers

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If we begin in spring, before the sea-ice has melted there is already plenty of growth going on. Phytoplankton (microscopic marine plants) begin to grow as soon as enough light penetrates through the ice. Some of these algae form substances which cause them to stick together and producing long “curtains”. These algae are already providing food for zooplankton, producing a complete ecosystem even before the ice has gone! You can see a movie of the algae here.

Once we move into summer it isn’t hard to imagine life flourishing here. Constant sunlight provides plenty of energy for photosynthesis, is always available and nutrients (at the beginning of the season) are plentiful. It is these conditions that can lead to some of the largest blooms of phytoplankton being seen within the Arctic Circle, as well as some very productive fisheries (e.g. the Barents Sea).

However, as the season begins to shift there are a variety of conditions to deal with. The freezing of water into ice, the cold temperatures and the changing light. Cells have a high composition of water within them, which when it freezes it will expand. This is not good for a single celled organism, as if the cell membrane is pierced by the ice they will die. Many cells have adapted to this by having mechanisms to protect the fluidity of the membrane (stop it from freezing) and producing substances known as extracellular polymeric substances which prevents ice from forming.

A beautiful feature known as frost flowers can arise during ice formation, these are crystallised moisture from the surface of new sea ice which has rapidly formed leading to a steep temperature gradient. Frost flowers have been found to contain up to 10⁶ bacterial cells per ml. These bacteria have also been found to have intriguing abilities, such as the reduction of mercury and uptake of sulphurous compounds.

Finally, we move into the period of darkness known as the polar night. It was long thought
that life almost shut down during this time, zooplankton and phytoplankton produced spores or resting stages which would wait for more favourable conditions. Like a bear going into hibernation. However, recently it has been shown that not all is quiet during the polar night.
Phytoplankton switch their life style from autotrophy (produce their own energy from sunlight) to mixotrophy (get energy by ingesting bacteria) and zooplankton still actively move within the water column, rather than resting. In fact it was recently found that the light from a bright full moon can cause a response in zooplankton. Investigations into the stomachs of sea-birds and fish during the polar night have found a high proportion are
full, suggesting they are still actively foraging. What was thought of as a time of rest has been shown to be anything but! It can be difficult to get into Polar Regions during this time to carry out research, but a handful of projects are actively looking at this with some exciting results!

Eventually the sun will begin to return, and the cycle of the Arctic will begin again. The Arctic is warming 3 times faster than the global average and this is impacting the timing and magnitude of sea-ice melt as well as increasing water temperatures. To see the current and projects changes in Arctic sea ice, see this video. There are a number of other impacts, such as the declining size of zooplankton and changing phytoplankton species which may impact food webs within the region.

Zooplankton images: arcodiv.org

Ice algae: https://www.mpg.de/6949942/Arctic-ecosystem-climate

Phytoplankton image: http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=51765

Frost flowers: http://www.npr.org/sections/krulwich/2012/12/17/167469845/suddenly-theres-a-meadow-in-the-ocean-with-flowers-everywhere

Berge J., et al., 2015. In the dark: A review of ecosystem processes during the Arctic polar night. Prog. Ocean. 139.

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The first question you may have is, “how is the light produced?” and the answer to this is chemistry. It is all due to a molecule called luciferin and an enzyme known as luciferase. Luciferase causes the reaction of oxygen with luciferin which produces energy released as a flash of light.

A wide diversity of organisms were shown during Widder’s talk, ranging from eels to single celled marine plants (dinoflagellates), and indeed bioluminescence is widespread in nature. From bacteria (such as found in the lure of deep sea angler-fish) to the larger vampire squid of the deep ocean. An interesting fact is that, aside from a few exceptions, bioluminescence is absent from freshwater environments.

The deep sea angler fish (left) and vampire squid (right).

The reason why the container of dinoflagellates lit up when Widder gave it a good shake is due to the chemical reaction discussed above. The physical action on the outside membrane of the cell causes ions (such as calcium, sodium) to generate a chemical charge and the reaction of luciferin to produce light. This all happens within 12 milliseconds! Although the flash of light from 1 cell may not look like much, if we scale it down to the size of a dinoflagellate (about 0.5 millimetres) the light can be seen by a fish up to 5m away. That would be equivalent to a 2m human being seen 20km away by flashing light, pretty impressive if you ask me!

Most of the bioluminescent light emitted in the oceans is within the blue and green spectrum of light, particularly in the deep ocean, as shown in Edith Widder’s talk. There is a reason for this and it is to do with the properties of light. When light hits the surface of the ocean (or any body of water) the light is absorbed sequentially through different wavelengths (see diagram). Red is the first to be absorbed, followed by orange, yellow, green and finally blue. This is why when you look at water it appears blue as all other wavelengths have been absorbed. As red light would not penetrate to the deep ocean, organisms here have not evolved to detect red light, so emitting red light to distract your predator would have no real effect here.

Finally, someone may ask “this is all great, but what has bioluminescence ever done for humanity?” Well, a small molecule known as green-fluorescent protein (GFP) was discovered and isolated from a jellyfish (Aequorea victoria) in 1962. This molecule (and others) have revolutionised biology. By attaching GFP to proteins it is possible to look at the movements and fates of compounds within cells. It is used to look at gene activation within cells and visualise growing tumours. In fact GFP has had such a profound impact on science that in 2008 the Nobel Prize in Chemistry was awarded to the discoverers of this molecule.

Image of the jellyfish Aequorea victoria and GFP-tagged keratin in a culture of skin (epithelial) cells

There are still many mysteries surrounding bioluminescence, but I hope this has been provided you with a little bit more information. If you have any further questions please ask in the comments section and we will try to answer them.

Many fun facts were taken from “Bioluminescence in the Sea, Haddock S., Moline M.A., Case, J.F. Ann. Rev. Mar. Sci. 2010”.

Information on the Nobel Prize awarded to Osamu Shimomura, Martin Chalfie and Roger Y. Tsein can be found here.

Dinoflagellates on the beach image: http://www.techeblog.com/index.php/tech-gadget/5-amazing-bioluminescent-things-that-actually-exist-in-nature

Image of the light absorbtion spectrum: http://www.seos-project.eu/modules/oceancolour/oceancolour-c01-p07.html

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The first issue I want to discuss is microplastics. These have been in the news a lot recently, but they are essentially tiny plastic particles which are found in personal hygiene products, such as face washes, toothpaste & body scrubs. The particles are used to exfoliate the dead cells. However, as we wash our faces in the bath or over a sink, the microplastics are flushed into the drain.

These small particles are not completely removed by waste water treatment plants and eventually make their way into the oceans, where they are accumulating. They are commonly mistaken for food by the zooplankton (microscopic animals of the ocean), molluscs, fish and even sea birds.

Image of microplastic ingestion by marine zooplankton (right), how microplastics can move around the marine foodweb (left)

There are alternatives, such as sand, salt or coconut. There are two ways you can help with this issue, the first is to look at the ingredients in any care products you buy, and the most common microplastics you might see on the back (and should avoid) are:

• Polyethylene / polythene (PE)
• Polypropylene (PP)
• Polyethylene terephthalate (PET)
• Polymethyl methacrylate (PMMA)
• Nylon

Or, if you have a smart phone, you can download an app known as “Beat the microbeads”. You simply scan the barcode of a product you wish to buy and it will tell you whether or not it contains any microbeads, and you therefore shouldn’t buy it. You can also take a look at the ‘Good Scrub Guide’ which provides a list of products free of microbeads (http://www.fauna-flora.org/initiatives/the-good-scrub-guide/).

Whilst we are on the topic of smart phone apps, Paris wrote an excellent blog post about eating sustainable fish (http://moocs.southampton.ac.uk/oceans/2015/10/10/eat-responsibly/) and the Marine Stewardship Council (MSC) have an app known as “MSC Seafood Finder” which provides lists of sustainably sourced seafood from a large number of retailers (all of the UK supermarkets are on here) and can help you decide which products to buy sustainably.  Also a recent campaign by Greenpeace is highlighting the best Tuna brands you can buy within the UK, take a look at it here (https://secure.greenpeace.org.uk/page/s/not-just-tuna) and avoid John West & Princes tuna until they change their sustainability policies!

It’s been great to have been with you on this journey over the last six weeks, and I hope you have learnt much about the oceans, and will help spread the knowledge you have so that we can have a healthier, more sustainable ocean in the future!

Information on microplastics from the Marine Conservation Society (https://www.mcsuk.org/what_we_do/Clean+seas+and+beaches/Campaigns+and+policy/Microplastics)

Image 1: http://www.fauna-flora.org/initiatives/the-good-scrub-guide/

Image 2: http://discardstudies.com/2013/07/22/the-plastisphere-and-other-21st-century-waste-ecosystems/

Image 3: https://plastictides.wordpress.com/2014/07/08/microplastic-ingestion/

Image 4: http://get.beatthemicrobead.org/

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Before we get in to marine viruses, let’s begin with what is a virus? A virus is an infectious intracellular parasite, meaning that it needs to get inside a living cell to replicate. It is essentially genetic information encapsulated in a protein coat. Due to the requirement of needing a ‘host’ cell, it is often said that viruses are not actually “alive” as they do not have the capability of self-replication like a bacterial cell.

Viruses are the most abundant biological entities in the oceans, there are approximately 10 million viruses per millilitre in surface seawater. If you were to take all of the carbon in marine viruses, it would be the equivalent of 75 million blue whales. If you took the average size of a marine virus and put them end to end then they would span 10 million light years. They are in such vast numbers, and so diverse, but we are only just beginning to fully appreciate how they regulate life in the oceans.

Viruses affect marine communities through various ways, there is of course the death of the cell, in a process known as lysis. This is where the cell essentially explodes and releases hundreds of viruses into the environment to look for a new host to infect. This is very important for the turning over of nutrients in the upper oceans, as the lysis of these cells causes the nutrients to be returned to the water column where they can be used again by bacteria or phytoplankton (microscopic marine plants).

Lytic life cycle of viruses

Viruses are also able to insert themselves into the genome of their hosts and affect the genes they are expressing, essentially controlling how the cell behaves. Finally, as viruses move between different cells rapidly they can act as methods of gene transfer. It has been discovered that some viruses of marine photosynthetic organisms actually carry with them almost all of the genes required for efficient photosynthesis.

Cartoon summarising the three major interactions of viruses with their hosts in the oceans.

I hope this article has hopefully shown to you the importance of viruses within the oceans, that they are not just disease causing agents but can regulate nutrient cycles and genetic transfer and that they are incredible interesting!

Photo 1 credit: http://linxc10.wix.com/microbes#!viruses/c1wjk

Photo 2 credit: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/V/Viruses.html

Photo 3 credit: Breitbart, M. 2012. Marine viruses: truth or dare. Ann. Rev. Mar. Sci. 4: 425–48.

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One concentrated drop of seawater, showing the diversity of life which can be found in the oceans (credit: David Littschwager, littschwager.com)

Although sometimes it is possible to see some of these plankton without the aid of a microscope, take for instance this sample collected from the Arctic.

Copepods collected through the use of a plankton net from Isfjorden in Svalbard, a close up image of one of these copepods is included as an inset

Although dominated by small animals of the sea (zooplankton) the copepods were there in such high abundance, collected from the top 10 metres of the water column!

This life can come in such wonderful and diverse forms. The image below shows the diversity of one group of microbial marine plants – phytoplankton – the diatoms. Which produce armoured shells of silica and can be found in a dazzling array of shapes.

Diatoms – phytoplankton with an armoured shell made of silica produce some wonderful and beautiful forms (credit microscopy-uk.org.uk)

The appearance of these organisms is enough to astound anyone, but sometimes it is what they do which captivates me. Certain species of dinoflagellates – another group of the phytoplankton – are able to produce light when they are disturbed, a process known as bioluminescence, and can display some of the most amazing images in nature.

Bioluminescent phytoplankton (dinoflagellates). Produce some of the most beautiful scenes in nature, here seen at Mosquito Bay, Vieques, Puerto Rico (credit Doug Perrine, Alamy).

It is both the beauty and the mystery of the plankton which makes studying them every day an amazing and rewarding experience.

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