Tiny grazers love to eat their greens

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, members of the Harvey and Whalen labs 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.

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!

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. 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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What do oceanographers do? They study tiny organisms!

 

I’ll be entering my senior year at Haverford College as an undergraduate in the biological sciences, and I’ve worked with Dr. Kristen Whalen since last summer right before she started as a biology professor. Under her guidance I have been studying compounds that marine bacteria produce (i.e. natural products) and their usefulness in combating antibiotic resistance in bacteria. So I don’t have any prior oceanographic experience and didn’t know much at all about phytoplankton before MesoHux2017. However, since coming to Norway I do know (and have learned the past couple of weeks) a little bit more about bacteria in the ocean!

In this mesocosm experiment, we are also interested in marine bacterial natural products, but for much different purposes than what I study in College. Bacteria produce a multitude of natural products, depending on bacterial species, where they live, and what kinds of stresses they are experiencing. Many of these are not essential for survival but are only produced under certain conditions, and sometimes we don’t know why bacteria produce them in the first place. They can produce things like antibiotics, molecules that scavenge for sparse nutrients such as iron, etc. and also infochemicals that allow them to communicate and coordinate with each other to enhance their survival as a community.

Bacteria like to colonize and live as communities of cells, so when they’re in the ocean they like to colonize on ocean surfaces – kind of like particle hitchhikers. One great example of a surface in the ocean is larger organisms such as phytoplankton! During bloom events, periods when these tiny algae are locally present in very large numbers, many bacteria associate with the phytoplankton and the two have a sort of love/hate relationship – they benefit from the recycling of nutrients from each other, but at the same time are competing for those same nutrients. These interactions between phytoplankton and bacteria are essential, since they mediate the marine food web structure as well as the cycling of carbon and other important compounds in the ocean.

Understanding the interactions of bacteria and phytoplankton and how bacteria can influence phytoplankton bloom development will give us more insight into how they might drive energy flow in the ocean and the cycling of compounds that influence climate change. These bacterial influences are not very well understood, so one thing that Liz Harvey and Kristen have been interested in is the sorts of chemicals that drive bacteria-phytoplankton interactions. Recently they discovered how HHQ, a known bacterial infochemical/quorum sensing molecule, can also control phytoplankton growth. You can read all about HHQ and how we will study its effects in the field over at Kristen’s blog post (link)!

For us to be able to study the questions that we are interested in, we need to go out on the boat early in the morning, collect a lot of water from the mesocosm bags, and filter, and filter, and filter to get the samples that we want (in our case, bacterial DNA and phytoplankton RNA from total of almost 500 liters of water!). I’ve never done any sort of field work before, and one thing that I did not expect is how much heavy lifting it involves. Oceanographers need to be tough and brave the elements for the sake of science. But even with this great courage we still have time for fun out on the dock – we always check up on our resident mesocosm seagull mom-to-be (pictured below), and some of us like to sing/dance along to music blasting from the tiny radio in the shed while others prefer to examine, identify, and take pictures of the jellyfish floating around in the water.

I’ve learned so much during my time at MesoHux2017, including (but not limited to) various new techniques in the lab, various new techniques in the kitchen, how to safely operate a motorboat and almost park it successfully, and, most importantly, the importance of scientific collaboration. Having the opportunity to participate on this team and attend the nightly science team meetings has given me insight on the process of real science and real collaboration. Since the nature of this research and phytoplankton bloom dynamics in general is so unknown, a lot of things happen that are unexpected and hard to explain, and it takes a lot of data sharing and constant exchange of ideas and questions to figure out what’s going on and decide on an often-changing game plan. It’s the sort of environment where when one person gets very encouraging data after a long time of hoping, she’s met by cheers and happy dances as she spreads the news around the lab. Watching this sort of real-time, collaborative problem solving has been eye-opening, and it’s really exciting to be a part of this project.

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Anna Schrecengost

 

What is this virus that infects the phytoplankton?

A few years ago science writer Rose Eveleth joined us  on a research cruise in the North Atlantic. Rose answered readers questions about the interactions of E. hux and the virus that infects it – the organisms we work on at the mesocosm. Read her blog post about viruses that infect phytoplankton. 

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Viruses are the most abundant biological thing in the ocean, but we know very little about them. For a long time, people thought phytoplankton were very long-lived. They died when they were eaten, or floated down too deep, but otherwise scientists couldn’t figure out what would make the little plants die. Turns out viruses kill lots of phytoplankton.                       Read more

 

What do oceanographers do? Sampling !

Sampling in the Whalen and Harvey Labs is in full swing. Our day begins at 0600 when members of both labs set out in a small boat to the mesocosm platform to collect the necessary water in acid-washed plastic carboys for all of our in-lab experiments. This happens in rain or shine, and we always hope for sunning warm weather, which is not always the case as in Norway, as residents can expect over 200 days of rain.

The Whalen Lab needs 60L of seawater from nutrient “replete” bags alone to prepare for the experiments ahead. We are interested in the molecule 2-heptyl-4-quinolone or HHQ for short. What is so special about HHQ….well, it is a known bacterial quorum sensing molecule – it helps bacteria talk with each other. Bacteria use special molecules to signal to other bacteria in the environment to coordinate behaviors – like turn on virulence genes, make antibiotics, or bioluminesce. Bacteria are always “listening” for these molecules with cell-surface receptors by monitoring their chemical environment in order to track changes in their numbers so they call collectively change their strategy at a moment’s notice.

At low densities of bacteria, quorum sensing molecules, like HHQ, diffuse away in the seawater, and therefore, are present at concentrations below the threshold required for detection. However, when bacteria are extremely abundant, the cumulative production of HHQ leads to locally high concentrations of the molecule in the microhabitat, thereby enabling detection by the bacterial community and inaction of a coordinated response.

 Up until now, HHQ was well known in the medical literature, having originally been discovered in the lungs of patients with severe bacterial infections. Here, HHQ can rapidly accumulate in the mucus surrounding bacterial cells and lead to the coordinated behavior including virulence factors necessary for a pathogenic lifestyle. Last year, we reported HHQ was present in cultures of marine bacteria, and were able to hunt down the genes responsible for this molecule’s production.

 We now know that HHQ does more than function simply as a communication molecule or “infochemical”. When we expose phytoplankton like Emiliania huxleyi, to low concentrations of HHQ, like 1 parts per billion, something interesting happens. This species of phytoplankton stops growing when exposed to low concentrations of HHQ and goes into what in laymen’s terms could be called stasis. The phytoplankton cell neither grows nor dies. This carries on for about three days, when finally death occurs.

 The Whalen and Harvey Labs are trying to understand how such a fundamental chemical used in bacterial communication might impact phytoplankton growth dynamics in the real world. That is where the Bergen Mesocosm’s come in. We have sufficient evidence for the effects of HHQ on individual species of phytoplankton, but we still don’t yet know how a community of phytoplankton and their bacterial buddies will respond in the presence of HHQ when we test this compound in the field. Our experiments for MesoHux2017 will address two general questions: (1) how does the bacterial community change during the course of E. huxleyi bloom in response to HHQ, and (2) how does phytoplankton physiology change at the molecular level in response to HHQ?

 To accomplish these aims, the Whalen lab has set out a very ambitious schedule of sample prep to obtain both DNA from bacterial communities to monitor how the “players” change in response to HHQ; and RNA which will show us what genes are being transcribed in response to HHQ exposure and how phytoplankton respond to bacterial chemical stressors. This requires us to filter lots of seawater from the mesocosm in a 10 deg C (50 deg F) on filters that can collect the material we want – 1 micron filter to retain phytoplankton and a 0.2 micron filter to get all the bacteria.

 Once we filter the water through special plastic filters, we pop these into special plastic tubes that can hold up to extreme cold conditions and drop them into our giant cryoshipper that can maintain a temperature of -120 deg Celsius for 50 days at a stretch. Back at Haverford College, both DNA and RNA will be isolated from filters and further processed to address the questions above.

Members of the Whalen/Harvey Labs have been working non-stop since their arrived, and everyone is pitching in to make the most of our limited time in the fjord. To keep spirits up, members take turns making dinner for the group of 8 scientists. We decided as a group to make a cake as a treat for celebrating our current sampling successes. Little did we know that the language barrier would be just an impediment to making a cake. For example. We thought we bought cake mix…turns out that was frosting. What we thought was frosting was actually custard mix. So we had to go back to the store to actually get cake mix. And the temperature the cake was baked at was for cupcakes and not a sheet pan. But in the end we figured it out and our “3 mistake cake” turned out awesome and the team was all smiles!

Signing off for now!

 Kristen Whalen

Mesocosms: The Middle World

Mesocosms- or a “medium world”- are at the heart of our fieldwork. Mesocosms are large enclosures that allow researchers to study the environment over a certain time period in a controlled way. The mesocosms we are working with are large bags, filled with natural seawater from the Norwegian fjord. The bags are closed off from the surrounding water and can be manipulated to test different hypotheses about how marine microbial communities function and respond to environmental factors. Mesocosm studies are useful tools to link patterns we see in laboratory cultures to the real world. Mesocosms truly represent a middle world for scientists!

One of our first tasks upon arriving to Norway was to setup and deploy the mesocosm bags. The bags are made of a thick, string reinforced plastic that are attached to floating frame and get filled from the bottom. The bags also have a detachable cone at the bottom 1 meter that will allow divers to collect sediments that have settled out (more on the importance of sediments later!). The cones were installed by professional commercial divers. The video below was captured by one of the divers during the time of deployment.

In Oceanography, you have to always expect the unexpected. During the mesocosm deployment, we had difficulty getting the bags, and the bottom settling cone, to sink. We had to come together to think of a quick solution to this problem. After trying several methods, taking multiple trips to the hardware store for weights,  and drilling several holes in the hoop frames, we were able to get the proper deployment!

Once the bags were deployed, we added nutrients (goodies for the phytoplankton!) to help give a jumpstart to a phytoplankton bloom. Three bags were excluded from nutrient additions (these are our control bags). Each bag was then equipped with bubblers to help mix the nutrient throughout the bag. Now we wait!

What do oceanographers do? They filter sea water

According to the National Oceanic and Atmospheric Administration (NOAA) , an oceanographer studies the ocean.  Some oceanographers study whales, sharks, fish and other large creatures, but we focus our research on microscopic life forms – phytoplankton and viruses. In order to collect enough of those tiny creatures, we need to concentrate large numbers of them in smaller volulme. We do this by filtering. We run a lot of sea water through filters that have very small pores and collect the tiny organisms that remain on the filters for analysis. When I say small pore size, I mean really small. We use a pore size of 1.2uM to collect phytoplankton cells. 1.2uM is 1.2/1,000,000 of a meter (or 0.00005 of an inch)* and 15 times smaller than the width of a thin human hair!  For other samples, such as viruses and non-living particles, we use an even smaller pore size – down to 0.02uM (those are the Anotop filters listed below). We will use thousands of filters to collect different samples while in Espegrend.

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Filters we shipped to the station for the project.

 

 

 

 

 

 

 

 

 

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Thanks to Sandra Lanman for her help with editing this post.

 

Espegrend – here we come!

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Espegrend, sometimes also called Espeland, is a Norwegian marine biological station. run by University of Bergen, Norway.  It is located about 20km south of Bergen.

Espeland has a number of specialized facilities and internationally well-known for is mesocosm facility.

From May 8 to June 2, 2017 a group of scientists (that’s us) will be at the station to study the interaction of the globally important phytoplankton Emiliania huxleyi (E. hux) with the viruses that infect and kill E. hux cells.  Read more about why and how we plan to to study this here.

We will post regular updates here  and we invite you to follow us on Facebook and Twitter

To see photos taken during a mesocosm experiment in 2008 in Espeland – click here.