Katie Gavenus, Bonus Blog: MIXOTROPHS, May 5, 2019

NOAA Teacher at Sea

Katie Gavenus

Aboard R/V Tiglax

April 26 – May 9, 2019

Mission: Northern Gulf of Alaska Long-Term Ecological Research project

Geographic Area of Cruise: Northern Gulf of Alaska – currently in transit from ‘Seward Line’ to ‘Kodiak Line’

Date: May 5, 2019

Weather Data from the Bridge

Time: 2305
Latitude: 57o 34.6915’
Longitude: 150o 06.9789’
Wind: 18 knots, South
Seas: 4-6 feet
Air Temperature: 46oF (8oC)
Air pressure: 1004 millibars
Cloudy, light rain

 

Science and Technology Log

I was going to just fold the information about mixotrophs into the phytoplankton blog, but this is so interesting it deserves its own separate blog!

On land, there are plants that photosynthesize to make their own food. These are called autotrophs – self-feeding.  And there are animals that feed on other organisms for food – these are called heterotrophs – other-feeding.  In the ocean, the same is generally assumed.  Phytoplankton, algae, and sea grasses are considered autotrophs because they photosynthesize.  Zooplankton, fish, birds, marine mammals, and benthic invertebrates are considered heterotrophs because they feed on photosynthetic organisms or other heterotrophs.  They cannot make their own food.  But it turns out that the line between phytoplankton and zooplankton is blurry and porous.  It is in this nebulous area that mixotrophs take the stage!

Mixotrophs are organisms that can both photosynthesize and feed on other organisms.  There are two main strategies that lead to mixotrophy.  Some organisms, such as species of dinoflagellate called Ceratium, are inherently photosynthetic.  They have their own chloroplasts and use them to make sugars.  But, when conditions make photosynthesis less favorable or feeding more advantageous, these Ceratium will prey on ciliates and/or bacteria.  Bacteria are phosphorous, nitrogen, and iron rich so it is beneficial for Ceratium to feed on them at least occasionally. Microscopy work makes it possible to see the vacuole filled with food inside the photosynthetic Ceratium. 

illustration of mixotrophic dinoflagellate Ceratium

I created this drawing after viewing a number of microscopy photos of the mixotrophic dinoflagellate Ceratium under different lights and stains. This artistic rendition combines those different views to show the outside structure of the dinoflagellate as well as the nucleus, food vacuole and chloroplasts. (Drawing by Katie Gavenus)

Other organisms, including many ciliates, were long known to be heterotrophic.  They feed on other organisms, and it is particularly common for them to eat phytoplankton and especially cryptophyte algae. Recent research has revealed, however, that many ciliates will retain rather than digest the chloroplasts from the phytoplankton they’ve eaten and use them to photosynthesize for their own benefit. Viewing these mixotrophs under blue light with a microscope causes the retained chloroplasts to fluoresce.  I saw photos of them and they are just packed with chloroplasts!

illustration of mixotrophic ciliate Tontonia sp.

The mixotrophic ciliate Tontonia sp. eats phytoplankton but retains the chloroplasts from their food in order to photosynthesize on their own! I made this drawing based off of photos, showing both the outside structure of the Tontonia and how the chloroplasts fluoresce as red when viewed with blue light. (Drawing by Katie Gavenus)

Mixotrophs are an important part of the Gulf of Alaska ecosystem.  They may even help to explain how a modestly productive ecosystem (in terms of phytoplankton) can support highly productive upper trophic levels. Mixotrophy can increase the efficiency of energy transfer through the trophic levels, so more of the energy from primary productivity supports the growth and reproduction of upper trophic levels. They also may increase the resiliency of the ecosystem, since these organisms can adjust to variability in light, nutrients, and phytoplankton availability by focusing more on photosynthesis or more on finding prey. Yet little is known about mixotrophs.  Only about one quarter of the important mixotroph species in the Gulf of Alaska have been studied in any way, shape or form!

Researchers are trying to determine what kinds of phytoplankton the mixotrophic ciliates and dinoflagellates are retaining chloroplasts from.  They are also curious whether this varies by location, season or year.  Understanding the conditions in which mixotrophic organisms derive energy from photosynthesis and the conditions in which they choose to feed is another area of research focus, especially because it has important ramifications for carbon and nutrient cycling and productivity across trophic levels.  And it is all very fascinating!

food web illustration

A drawing illustrating a fascinating, tightly linked portion of the Gulf of Alaska food web. Mesodinium rubrum must eat cryptophyte algae (this is called obligate feeding). The Mesodinium rubrum retain the chloroplasts from the cryptophyte algae, using them to supplement their own diet through photosynthesis. In turn, Dinophysis sp. must feed on Mesodinium rubrum. And the Dinophysis retain the chloroplasts from the Mesodinium that originally were from cryptophyte algae! (Drawing by Katie Gavenus)

Did you know?

Well over half of the oxygen on earth comes from photosynthetic organisms in the ocean.  So next time you take a breath, remember to thank phytoplankton, algae, and marine plants!

Personal Log:

Tonight was likely our last full night of work, as we expect rough seas and high winds will roll in around midnight tomorrow and persist until the afternoon before we head back to Seward.  We were able to get bongo net sampling completed at 6 stations along the Kodiak Line, and hope that in the next two nights we can get 2-4 stations done before the weather closes in on us and 2-4 nets on the last evening as we head back to Seward.

Despite our push to get 6 stations finished tonight, we took time to look more closely at one of the samples we pulled up.  It contained a squid as well as a really cool parasitic amphipod called Phronima that lives inside of a gelatinous type of zooplankton called doliolids.  Check out the photos and videos below for a glimpse of these awesome creatures (I couldn’t figure out how to mute the audio, but I would recommend doing that for a less distracting video experience).

 

 

Phronima

A parasitic Phronima amphipod. This animal typically lives inside doliolids, a type of gelatinous zooplankton. Apparently its body structure and fierce claw-like appendages inspired the design of “Predator.”

 

 

 

 

Katie Gavenus: Don’t Forget the Phytoplankton! May 5, 2019

NOAA Teacher at Sea

Katie Gavenus

Aboard R/V Tiglax

April 26 – May 9, 2019

Mission: Northern Gulf of Alaska Long-Term Ecological Research project

Geographic Area of Cruise: Northern Gulf of Alaska – currently in transit from ‘Seward Line’ to ‘Kodiak Line’

Date: May 5, 2019

Weather Data from the Bridge

Time: 2305
Latitude: 57o 34.6915’
Longitude: 150o 06.9789’
Wind: 18 knots, South
Seas: 4-6 feet
Air Temperature: 46oF (8oC)
Air pressure: 1004 millibars
Cloudy, light rain

Science and Technology Log

Phytoplankton!  These organisms are amazing.  Like terrestrial plants, they utilize energy from the sun to photosynthesize, transforming water and carbon dioxide into sugars and oxygen.  Transforming this UV energy into sugars allows photosynthetic organisms to grow and reproduce, then as they are consumed, the energy is transferred through the food web.  With a few fascinating exceptions (like chemotrophs that synthesize sugars from chemicals!), photosynthetic organisms form the basis of all food webs. The ecosystems we are most familiar with, and depend upon culturally, socially, and economically, would not exist without photosynthetic organisms.

Indeed, productivity and health of species like fish, birds, and marine mammals are highly dependent upon the productivity and distribution of phytoplankton in the Gulf of Alaska. Phytoplankton also play an important role in carbon fixation and the cycling of nutrients in the Gulf of Alaska.  For the LTER, developing a better understanding of what drives patterns of phytoplankton productivity is important to understanding how the ecosystem might change in the future.  Understanding the basis of the food web can also can inform management decisions, such as regulation of fisheries.

niskin bottles on the rosette

Seawater captured at different depths by niskin bottles on the rosette transferred to bottles by different scientists for analysis.

To better understand these patterns, researchers aboard R/V Tiglax use the rosette on the CTD to collect water at different depths.  The plankton living in this water is processed in a multitude of ways.  First, in the lab on the ship, some of the water is passed through two filters to catch phytoplankton of differing sizes.  These filters are chemically extracted for 24 hours before being analyzed using a fluorometer, which measures the fluorescence of the pigment Chlorophyll-a.  This provides a quantitative measurement of Chlorophyll-a biomass. It also allows researchers to determine whether the phytoplankton community at a given time and place is dominated by ‘large’ phytoplankton (greater than 20 microns, predominantly large diatoms) or ‘small’ phytoplankton (less than 20 microns, predominantly dinoflagellates, flagellates, cryptophyte algae, and cyanobacteria).

Preparing filters

Preparing filters to separate large and small phytoplankton from the seawater samples.

For example, waters in Prince William Sound earlier in the week had a lot of large phytoplankton, while waters more offshore on the Seward Line were dominated by smaller phytoplankton.  This has important ramifications for trophic interactions, since many different consumers prefer to eat the larger phytoplankton.  Larger phytoplankton also tends to sink faster than small plankton when it dies, which can increase the amount of food reaching benthic organisms and increase the amount of carbon that is sequestered in ocean sediments.

The Chlorophyll-a biomass measurements from the fluorometer are a helpful first step to understanding the biomass of phytoplankton at stations in the Gulf of Alaska.  However, research here and elsewhere has shown that the amount of carbon fixed by phytoplankton can vary independently of the Chlorophyll-a biomass.  For example, data from 2018 in the Gulf of Alaska show similar primary productivity (the amount of carbon fixed by phytoplankton per day) in the spring, summer, and fall seasons even though the Chlorophyll-a biomass is much higher in the spring.  This is likely because of at least two overlapping factors.  Vertical mixing in the winter and spring, driven primarily by storms, brings more nutrients and iron into the upper water column. This higher nutrient and iron availability in the spring allow for the growth of larger phytoplankton that can hold more chlorophyll.  This vertical mixing also means that phytoplankton tend to get mixed to greater depths in the water column, where less light is available.  To make up for this light limitation, the phytoplankton produce more chlorophyll in the spring so they can more effectively utilize the light that is available.  This variation in chlorophyll over the seasons probably helps to make the phytoplankton community overall more productive, but it makes it problematic to use Chlorophyll-a biomass (which is relatively easy to measure) as a proxy for primary productivity (which is much more challenging to measure).

Phytoplankton sample in the flourometer

A sample of filtered, extracted phytoplankton is placed into the fluorometer.

To address the question of primary productivity more directly, researchers are running an experiment on the ship.  Seawater containing phytoplankton from different depths is incubated for 24 hours.  The container for each depth is screened to let in sunlight equivalent to what the plankton would be exposed to at the depth they were collected from.  Inorganic carbon rich in C13 isotope is added to each container as it incubates. After 24 hours, they filter the water and measure the amount of C13 the phytoplankton have taken up.  Because C13 is rare in ecosystems, this serves as a measurement of the carbon fixation rate – which can then be converted into primary productivity.

Phytoplankton samples from the rosette are also preserved for later analysis in various labs onshore.  Some of the samples will be processed using High Performance Light Chromotography, which produces a pigment profile.  These pigments are not limited to Chlorophyll-a, but also include other types of Chlorophyll, Fucoxanthin (a brownish pigment found commonly in diatoms as well as other phytoplankton), Peridinin (only found in photosynthetic dinoflagellates), and Diadinoxanthin (a photoprotective pigment that absorbs sunlight and dissipates it as heat to protect the phytoplankton from excessive exposure to sunlight).  The pigment profiles recorded by HPLC can be used to determine which species of plankton are present, as well as a rough estimate of their relative abundance.

A different lab will also analyze the samples using molecular analysis of ribosomal RNA.  There are ID sequences that can be used to identify which species of phytoplankton are present in the sample, and also get a rough relative abundance.  Other phytoplankton samples are preserved for microscopy work to identify the species present.  Microscopy with blue light can also be used to investigate which species are mixotrophic – a fascinating adaptation I’ll discuss in my next blog post!

It is a lot of work, but all of these various facets of the phytoplankton research come together with analysis of nutrients, iron, oxygen, dissolved inorganic carbon, temperature, and salinity to answer the question “What regulates the patterns of primary productivity in the Gulf of Alaska?”

There are already many answers to this question.  There is an obvious seasonal cycle due to light availability.  The broad pattern is driven by the amount of daylight, but on shorter time-scales it is also affected by cloud cover.  As already mentioned, vigorous vertical mixing also limits the practical light availability for phytoplankton that get mixed to greater depths.  There is also an overall, declining gradient in primary productivity moving from the coast to the deep ocean. This gradient is probably driven most by iron limitation.  Phytoplankton need iron to produce chlorophyll, and iron is much less common as you move into offshore waters.  There are also finer-scale spatial variations and patchiness, which are partly driven by interacting currents and bathymetry (ocean-bottom geography). As currents interact with each other and features of the bathymetry, upwelling and eddies can occur, affecting such things as nutrient availability, salinity, water temperature, and intensity of mixing in the water column.

View of horizon from station GAK

The early-morning view from station GAK on the ‘Seward Line.’ Patterns of primary productivity are driven both by amount of cloud cover and amount of daylight. During our two weeks at sea, we actually sampled at GAK1 3 separate times. The amount of daylight (time between sunrise and sunset each day) at this location increased by nearly 60 minutes over the two week cruise!

The current work seeks to clarify which of these factors are the most dominant drivers of the patterns in the Gulf of Alaska and how these factors interact with each other. The research also helps to determine relationships between things that can be more easily measured, such as remote-sensing of chlorophyll, and the types of data that are particularly important to the LTER in a changing climate but are difficult to measure across broad spatial scales and time scales, such as primary productivity or phytoplankton size community. Phytoplankton are often invisible to the naked eye.  It would be easy to overlook them, but in many ways, phytoplankton are responsible for making the Gulf of Alaska what it is today, and what it will be in the future.  Understanding their dynamics is key to deeper understanding of the Gulf.

Personal Log

The schedule along the Seward Line and as we head to the Kodiak Line had to be adjusted due to rough seas and heavy winds.  This means we have been working variable and often long hours on the night shift. It is usually wet and cold and dark, and when it is windy the seawater we use to hose down the zooplankton nets seems to always spray into our faces and make its way into gloves and up sleeves.  But we still manage to have plenty of fun on the night shift and share lots of laughs.  There are also moments where I look up from the task at hand and am immersed in beauty, wonder, and fascination. I get to watch jellies undulate gracefully off the stern (all the while, crossing my fingers that they don’t end up in our nets  — that is bad for both them and us) and peer more closely at the zooplankton we’ve caught.  I am mesmerized by the color and motion of the breaking waves on a cloudy dawn and delighted by the sun cascading orange-pink towards the water at sunset.  I am reminded of my love, both emotional and intellectual, for the ocean!

Float coats

We experienced a lot of wind, rain, waves, and spray from the high-pressure hose (especially when I was wielding the hose), but bulky float coats kept us mostly warm and dry.

Did You Know?

Iron is the limiting nutrient in many offshore ecosystems.  Where there is more iron, there is generally more primary productivity and overall productive ecosystems.  Where there is little iron, very little can grow.  This is different than terrestrial and even coastal ecosystems, where iron is plentiful and other nutrients (nitrogen, phosphorous) tend to be the limiting factors.  Because people worked from what they knew in terrestrial ecosystems, until about 30 years ago, nitrogen and phosphorous were understood to be the important nutrients to study.  It was groundbreaking when it was discovered that iron may be a crucial piece of the puzzle in many open ocean ecosystems.

Question of the Day:

Regarding sustainability and scalability of intensive ocean resource harvesting: If humans started eating plankton directly, what could happen? And a follow-up: Can we use algae from harmful bloom areas?

Question from Leah Lily, biologist, educator, and qualitative researcher, Bellingham, WA

I first shared this question with the zooplankton night crew.  The consensus was that it was not a good idea to harvest zooplankton directly for large-scale human consumption.  Some krill and other zooplankton are already harvested for ‘fish oil’ supplements; as demand increases, the sustainability of this practice has become more dubious.  The zooplankton night crew were concerned that if broader-scale zooplankton harvest were encouraged, the resource would quickly be overharvested, and that the depletion of zooplankton stocks would have even more deleterious consequences for overall ecosystem function than the depletion of specific stocks of fish. They also brought up the question of how much of each zooplankton would actually be digestible to humans.  Many of these organisms have a chitinous exoskeleton, which we wouldn’t be able to get much nutrition from.  So it seems like intensive ocean harvesting of zooplankton is likely not advisable.

However, when I talked with the lead phytoplankton researcher on board, she thought there might be slightly more promise in harvesting phytoplankton.  It is more unlikely, she thinks, that it would get rapidly depleted since there is so much phytoplankton out there dispersed across a very wide geographic scale.  Generally, harvesting lower on the food chain is more energy efficient. At every trophic level, when one organism eats another, only a fraction of the energy is utilized to build body mass. So the higher up the food web we harvest from, the more energy has been ‘lost’ to respiration and other organism functions.  Harvesting phytoplankton would minimize the amount of energy that has been lost in trophic transfer.  Unlike most zooplankton, most phytoplankton is easily digestible to people and is very rich in lipids and proteins.  It could be a good, healthy food source.  However, as she also pointed out, harvesting phytoplankton in the wild would likely require a lot of time, energy, and money because it is generally so sparse.  It likely would not be economically feasible to filter the plankton in the ocean out from the water, and, with current technologies, not particularly environmentally friendly.  Culturing, or ‘farming,’ phytoplankton might help to address these problems, and in fact blue-green algae/Spirulina is already grown commercially and available as a nutritional supplement.  And there may be some coastal places where ‘wild’ harvest would be practical.  There are a number of spots where excess nutrients, often from fertilizers applied on land that runoff into streams and rivers, can cause giant blooms of phytoplankton.  These are often considered harmful algal blooms because as the phytoplankton die, bacteria utilize oxygen to decompose them and the waters become hypoxic or anoxic.  Harvesting phytoplankton from these types of harmful algal blooms would likely be a good idea, mitigating the impacts of the HABs and providing a relatively easy food source for people.  However, it would be important to make sure that toxin-producing plankton, such as Alexandrium spp. (which can cause paralytic shellfish poisoning) were not involved in the HAB.

Katie Gavenus: There’s More Than One Way to Catch a Copepod, May 2, 2019

NOAA Teacher at Sea
Katie Gavenus
Aboard R/V Tiglax
April 26 – May 9, 2019

Mission: Northern Gulf of Alaska Long-Term Ecological Research project
Geographic Area of Cruise: Northern Gulf of Alaska – currently on the ‘Seward Line’
Date: May 2, 2019

Weather Data from the Bridge
Time: 2053
Latitude: 58o 53.2964’ N
Longitude: 148o 34.4176’ W
Wind: 10 knots, West
Seas: 4-5 feet (Beaufort Scale 5)
Air Temperature: 7oC (44o F)
Air pressure: 1016 millibars
Overcast, no precipitation

Science and Technology Log

We were able to deploy the bongo net at 3 more stations on the Middleton Line before rough seas compelled us to head to some of the more sheltered sampling stations in Prince William Sound. (Sidenote: we did see a handful of myctophids in the last two hauls we did on the Middleton Line. Those are the lantern fish I was keeping a special eye out for after learning that they can be important black-legged kittiwake food this time of year.)

Though it complicates the schedule for the rest of the cruise, spending last night and today in Prince William Sound turned out to be fortuitously timed for this blog about zooplankton.

Along the Middleton Line, the night zooplankton crew deployed the bongo net, which does a cumulative sample from the surface through the water column to a specified depth and back up to the surface again. In general, the depth that we are deploying the bongo net to is 5-10 meters above the ocean floor but in deeper water we stop at approximately 200 meters. My understanding is that the bongo net is a good and straightforward way to get an overall look at zooplankton abundance and community structure.

In Prince William Sound , we deployed a Multinet instead, which has several nets with only one of them open at any given time. When the Multi reaches a specific depth range (like 200-150 meters), a computer signals the first net to open and it is towed until it reaches the next target depth after enough water has passed through it. That net is then closed, and a second net is opened at the next shallower depth. So on and so forth, until the Multinet has collected a sample at each of 5 discrete depth layers in the water column. Both the collection of samples and processing of them on deck take longer than the bongo nets. However, the major advantage of the Multi is that researchers can get a better sense of what is happening at different depths in the water column, rather than lumping zooplankton over 200 meters of depth all together like the bongo does.

Ability to analyze zooplankton abundance and community structure at different depths is important for a number of reasons. In a nearshore ecosystem like Prince William Sound, there are often significant gradients of salinity, temperature, nutrients, dissolved oxygen, and trace minerals as well as primary productivity. Data from the CTD and water sampling at various depths at each location can be compared to where certain species or life stages of zooplankton were found using the Multi, and this can help the LTER project to better understand what conditions support different types of zooplankton.

Another reason that a Multinet can be a useful tool relates specifically to the life history of common copepods in Prince William Sound and the Gulf of Alaska. Common in both coastal and offshore waters in this region, three species of the copepod Neocalanus gorge on the spring bloom of phytoplankton in order to build up lipid stores. These copepods go through different life stages. During the day, a different set of nets (called a CalVET) with finer mesh are deployed to 100 m and brought up vertically through the water column to catch zooplankton. Copepods from the CalVET sample are sorted by species and life stage to better understand inter-annual variability in their seasonal cycle and distribution.

CalVET net in the water
The CalVET nets have a finer mesh for catching smaller zooplankton and are deployed vertically through 100 m of water
Close up of CalVET net
The CalVET nets have a finer mesh for catching smaller zooplankton and are deployed vertically through 100 m of water

At the Prince William Sound station, almost all of the Neocalanus observed were in the N. flemingeri copepodite-5 stage, which is the stage just before they reach adulthood. In the next month, the C5 females in particular will store as much lipid as they can. In June, perhaps even late May, the N. flemingeri will molt into adults and swim down in the water column to approximately 400 meters or greater in depth. Here the female adult copepods will diapause, a hibernation-like process through which their metabolic activity slows significantly as they ‘overwinter’. They spend July through February or March in deep water. They do not feed in this adult stage, so as C5s the females must accumulate enough lipids to last through 7-9 months of diapause and the production of eggs! They tend to lay eggs beginning in December through January or February, and die soon after they release the eggs. The males on the other hand die in June shortly after mating and do not diapause.

An aspect of the LTER research related to copepods analyzes how successful different Neocalanus spp. are when it comes to finding enough food to build up lipid stores. One approach to answering this question involves photographing Neocalanus spp. with a specialized microscope and measuring the length and width of their lipid ‘bubble’ relative to their body size. This visual assessment is really cool, because you can actually get a solid sense of it here on the boat. Another approach utilizes analysis of gene expression called transcriptomics to ascertain if the copepods are food-stressed. Different markers will indicate whether the copepods are building or burning lipids. The copepods for this analysis are collected on the cruise, but must be processed in a lab on land, so it can be a while before the data is ready.

A scientist sits at a microscope connected to a computer; another scientist manages a laptop displaying the microscope's view
Copepods are photographed using a computer and microscope. This process allows researchers to get a sense of the amount of lipids the copepods have stored.
View of a copepod under a microscope, as displayed on a laptop, allows scientists to see its lipid storage
Examining the silver ‘bubble’ on each copepod, it is apparent that the C5 Neocalanus flemingeri in this photo has had more success at building lipid stores than the copepod in the photo below.
View of a copepod under a microscope, as displayed on a laptop, allows scientists to see its lipid storage
The copepod in this photo has a relatively smaller ‘silver bubble’ – lipid storage – than the specimen in the photo above.

Whether or not C5 Neocalanus spp. are able to sufficiently fatten up is a crucial question. If they can’t store enough lipids in April, May, and June, the adult females will not make it through diapause to reproduce. If this is true for a large portion of the females, it can dramatically impact copepod abundance the following year. And of course, these future changes in copepod abundance could impact carbon cycling and will likely ripple through the food web. Even more immediately, many species of vertebrates rely on lipid-rich C5 Neocalanus spp. each spring. If the C5s are starving, birds and fish that depend on these fatty snacks may not be able to feed enough for their own reproductive success.

Although the abundance of Neocalanus spp. caught in the CalVET was lower than expected for Prince William Sound, the ones that were caught generally displayed robust lipid stores. Out along the Middleton Line, the copepods had smaller lipid stores and most of them were a life stage earlier in development. Generally, Prince William Sound has an earlier phytoplankton bloom than the more offshore areas, so it isn’t surprising that the Middleton Line copepods aren’t as fat yet. As we sample at the Seward and Kodiak Lines, I will be peering over shoulders at the microscope to get a glimpse at the oh-so-important bubbles of lipid in the copepods.

Consider now that you’ve read multiple paragraphs about the unique natural history of just one subset of zooplankton – Neocalanus flemingeri and other species in the genus Neocalanus! These organisms are a crucial part of the flow of energy, carbon, and nutrients through the ecosystem. But they are just one part of a much more diverse zooplankton community. Alongside Neocalanus spp. we’ve seen a plethora of other copepods, euphausiids (krill), decapods (usually larval shrimp), and ostracods, as well as sea jellies, ctenophores (comb jellies), chaetognaths (arrow worms), and larval fish. And that’s not even discussing microzooplankton like ciliates! As a community, and as individual species, these zooplankton are important players in the Northern Gulf of Alaska. I am constantly impressed by the depth of knowledge the LTER zooplankton researchers have about these organisms, and simultaneously astounded by how much is still a mystery. The world of zooplankton is fascinating, and so many wonderful questions remain!

Sampled zooplankton viewed through a microscope
This small portion of zooplankton sample collected with the Multinet demonstrates the sheer abundance and diversity of these organisms!

Personal Log

I think I’ve finally shifted over to a more nocturnal schedule. I slept most of the day, but once again managed to wake up just in time to see some whales as I drank my ‘morning’ tea. There were a couple of minke whales, which is cool in and of itself, but the magnificence of the minkes was eclipsed by the sighting of a sperm whale. Sperm whales are somewhat common out in the Gulf, where they dive thousands of feet in search of squid. However, it is very unusual to see them in the shallower waters of Prince William Sound.

After dinner, the Tiglax veared in to Icy Bay for some additional CTD and CalVET samples. This was a special treat, as it allowed for a spectacular view of Chenega Glacier as well as the harbor seals and birds that hang out amongst the chunks of ice in the bay. We had another chance to go out in the zodiac skiff and were able to slowly make our way through some of the smaller icebergs for a closer look at the glacier. It was an incredible evening!

Four scientists, wearing protective float coats, ride on a small motorboat  closer to the glacier
The view from Icy Bay was beautiful, and a handful of us were able to get closer to Chenega Glacier in the zodiac skiff.

Did You Know?

Zooplankton utilize many different strategies to find food. Many species of copepods feed primarily on phytoplankton. Some of these herbivores utilize chemoreceptors to ‘smell’ the phytoplankton while others rely more heavily on mechanical receptors positioned along their antennae to listen for their food. Other copepods are predatory, with sharp claws for grabbing their prey. Many other species of zooplankton are predatory too; they attack, entangle, or paralyze other zooplankton to consume. But the options aren’t limited to herbivore or carnivore! Last night, as we were checking out one of the zooplankton samples, we found a copepod with a parasitic isopod; this isopod sucks nourishment from the copepod as an intermediate source before moving on to its final host, a glass shrimp. Though I didn’t see one in person, I was also told about a parasitic copepod that lives in the gills of cod.

Question of the Day:

Does oyster farming reduce local plankton biomass to a degree that is visible in adult populations of organisms like steamer clams?

Question from Kim McNett, artist & science educator, Homer, Alaska.

Though no one aboard specializes in oyster diets, I shared this question at dinner and the plankton experts were willing to make some conjectures. Clam trochophore larvae are fairly soft-bodied, so it is likely that oysters could consume them. A first step to answering this question would be to find out what size range of plankton oysters consume and compare that to the size of clam trochophores for the species of interest. If the clam trochophores are significantly larger (or smaller, but that is unlikely) than the size-fraction targeted by oysters, there probably isn’t much predation going on. But if the trochophores line up with the size eaten by oysters, then predation is definitely possible. Another step would be to figure out if clam larvae overlap in space and time with hungry oysters.

We also discussed whether or not oysters might compete with clams for food, and adversely affect the clams in this way. Generally, the consensus was that there might be some impact immediately around oyster lanterns but that over larger scales the impact would be negligible. Because oysters are farmed in lanterns suspended in the water column, and clams are located in the benthos and intertidal areas, there may be some niche partitioning. That is to say – the oysters are likely feeding on different plankton than what would reach the clams. To answer this question more fully, once could look at what size-fraction of plankton oysters feed on and compare it to the size-fraction consumed by clams. One could also look at the movement of water to try to determine whether the same plankton that drifts through oyster lanterns is likely to also drift into the intertidal and benthic locations where clams are located.

Katie Gavenus: Thinking Like A Hungry Bird, April 28, 2019

NOAA Teacher at Sea

Katie Gavenus

Aboard R/V Tiglax

April 26-May 9, 2019

 

Mission: Northern Gulf of Alaska Long-Term Ecological Research project

Geographic Area of Cruise: Northern Gulf of Alaska – currently on the ‘Middleton [Island] Line’

Date: April 28, 2019

 

Weather Data from the Bridge

Time: 1715
Latitude: 59o 39.0964’ N
Longitude: 146o05.9254’ W
Wind: Southeast, 15 knots
Air Temperature: 10oC (49oF)
Air pressure: 1034 millibars
Cloudy, no precipitation

 

Science and Technology Log

Yesterday was my first full day at sea, and it was a special one! Because each station needs to be sampled both at night and during the day, coordinating the schedule in the most efficient way requires a lot of adjustments. We arrived on the Middleton Line early yesterday afternoon, but in order to best synchronize the sampling, the decision was made that we would wait until that night to begin sampling on the line. We anchored near Middleton Island and the crew of R/V Tiglax ferried some of us to shore on the zodiac (rubber skiff).

This R&R trip turned out to be incredibly interesting and relevant to the research taking place in the LTER. An old radio tower on the island has been slowly taken over by seabirds… and seabird scientists. The bird biologists from the Institute for Seabird Research and Conservation have made modifications to the tower so that they can easily observe, study, and band the black-legged kittiwakes and cormorants that choose to nest on the shelfboards they’ve augmented the tower with. We were allowed to climb up into the tower, where removable plexi-glass windows look out onto each individual pair’s nesting area. This early in the season, the black-legged kittiwakes are making claims on nesting areas but have not yet built nests. Notes written above each window identified the birds that nested there last season, and we were keen to discern that many of the pairs had returned to their spot.

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Black-legged kittiwakes are visible through the observation windows in the nesting tower on Middleton Island.

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Nesting tower on Middleton Island.

The lead researcher on the Institute for Seabird Research and Conservation (ISRC) project was curious about what the LTER researchers were finding along the Middleton Line stations. He explained that the birds “aren’t happy” this spring and are traveling unusually long distances and staying away for multiple days, which might indicate that these black-legged kittiwakes are having trouble finding high-quality, accessible food. In particular, he noted that he hasn’t seen any evidence they’ve been consuming the small lantern fish (myctophids) that generally are an important and consistent food source from them in the spring. These myctophids tend to live offshore from Middleton Island and migrate to the surface at night. We’ll be sampling some of that area tonight, and I am eager to see if we might catch any in the 0.5 mm mesh ‘bongo’ nets that we use to sample zooplankton at each station.

The kittiwakes feed on myctophids. The myctophids feed on various species of zooplankton. The zooplankton feed on phytoplankton, or sometimes microzooplankton that in turn feeds on phytoplankton. The phytoplankton productivity is driven by complex interactions of environmental conditions, impacted by factors such as light availability, water temperature and salinity as well as the presence of nutrients and trace metals. And these water conditions are driven by abiotic factors – such as currents, tides, weather, wind, and freshwater input from terrestrial ecosystems – as well as the biotic processes that drive the movement of carbon, nutrients, and metals through the ecosystem.

Scientists deploy CTD

This CTD instrument and water sampling rosette is deployed at each station during the day to collect information about temperature and salinity. It also collects water that is analyzed for dissolved oxygen, nitrates, chlorophyll, dissolved inorganic carbon, dissolved organic carbon, and particulates.

CTD at sunset

When the sun sets, the CTD gets a break, and the night crew focuses on zooplankton.

Part of the work of the LTER is to understand the way that these complex factors and processes influence primary productivity, phytoplankton, and the zooplankton community structure. In turn, inter-annual or long-term changes in phytoplankton and zooplankton community structure likely have consequences for vertebrates in and around the Gulf of Alaska, like seabirds, fish, marine mammals, and people. In other words, zooplankton community structure is one piece of understanding why the kittiwakes are or are not happy this spring. It seems that research on zooplankton communities requires, at least sometimes, to consider the perspective of a hungry bird.

Peering at a jar of copepods and euphausiids (two important types of zooplankton) we pulled up in the bongo nets last night, I was fascinated by the way they look and impressed by the amount of swimming, squirming life in the jar. My most common question about the plankton is usually some variation of “Is this …” or “What is this?” But the questions the LTER seeks to ask are a little more complex.

Considering the copepods and euphausiids, these researchers might ask, “How much zooplankton is present for food?” or “How high of quality is this food compared to what’s normal, and what does that mean for a list of potential predators?” or “How accessible and easy to find is this food compared to what’s normal, and what does that mean for a list of potential predators?” They might also ask “What oceanographic conditions are driving the presence and abundance of these particular zooplankton in this particular place at this particular time?” or “What factors are influencing the life stage and condition of these zooplankton?”

Euphausiids

Euphausiids (also known as krill) are among the types of zooplankton we collected with the bongo nets last night.

Copepods in a jar

Small copepods are among the types of zooplankton we collected with the bongo nets last night.

As we get ready for another night of sampling with the bongo nets, I am excited to look more closely at the fascinating morphology (body-shape) and movements of the unique and amazing zooplankton species. But I will also keep in mind some of the bigger picture questions of how these zooplankton communities simultaneously shape, and are shaped by, the dynamic Gulf of Alaska ecosystem. Over the course of the next 3 blogs, I plan to focus first on zooplankton, then zoom in to primary production and phytoplankton, and finally dive more into nutrients and oceanographic characteristics that drive much of the dynamics in the Gulf of Alaska.

 

Personal Log 

Life on the night shift requires a pretty abrupt change in sleep patterns. Last night, we started sampling around 10 pm and finished close to 4 am. To get our bodies more aligned with the night schedule, the four of us working night shift tried to stay up for another hour or so. It was just starting to get light outside when I headed to my bunk. Happily, I had no problem sleeping until 2:30 this afternoon! I’m hoping that means I’m ready for a longer night tonight, since we’ll be deploying the bongo nets in deeper water as we head offshore along the Middleton Line.

WWII shipwreck

While on Middleton Island, we marveled at a WWII shipwreck that has been completely overtaken by seabirds for nesting.

Shipwreck filled with plants

Inputs of seabird guano, over time, have fertilized the growth of interesting lichens, mosses, grasses, and even shrubs on the sides and top of the rusty vessel.

 

Did You Know?

Imagine you have a copepod that is 0.5 mm long and a copepod that is 1.0 mm long. Because the smaller copepod is half as big in length, height, and width, overall that smaller copepod at best offers only about 1/8th as much food for a hungry animal. And that assumes that it is as calorie-dense as the larger copepod.

 

Question of the Day:

Are PCBs biomagnifying in top marine predators in the Gulf of Alaska? Are there resident orca populations in Alaska that are impacted in similar ways to the Southern Resident Orca Whale population [in Puget Sound] (by things like toxins, noise pollution, and decreasing salmon populations? Is it possible for Southern Resident Orca Whales to migrate and successfully live in the more remote areas of Alaska? Questions from Lake Washington Girl’s Middle School 6th grade science class.

These are great questions! No one on board has specific knowledge of this, but they have offered to put me in contact with researchers that focus on marine mammals, and orcas specifically, in the Gulf of Alaska. I’ll keep you posted when I know more!

Katie Gavenus: Just Around the Corner (or two!): April 22, 2019

NOAA Teacher at Sea

Katie Gavenus

Aboard R/V Tiglax

April 26 – May 9, 2019

Mission: Northern Gulf of Alaska Long-Term Ecological Research (LTER) Program.

Geographic Area of Cruise: Northern Gulf of Alaska (Port: Seward)

Date: April 22, 2019

Personal Introduction

Later this week, R/V Tiglax will depart the Homer Harbor in Homer, Alaska and begin the trip ‘around the corner.’  From the Homer Harbor, she will enter Kachemak Bay, flow into the larger Cook Inlet, and enter the Northern Gulf of Alaska and the North Pacific Ocean. Veering to the east, and then north, she will arrive in Seward, Alaska. That trip will take about 3 days, with stops along the way for some research near the Barren Islands. Meanwhile, I’ll be working in Homer for a few extra days before I begin my own trip to Seward. I will travel on the road system, first heading north and then jaunting southeast to Seward.  It will take me 3.5 hours to drive there.

However you get there, Seward and the Northern Gulf of Alaska Long-Term Ecological Research project area are just around the corner from Homer.  Homer is the place where I was born and raised, the place where I became inspired by science, the place where I now have the incredible privilege of working as an environmental educator for students participating in field trips and intensive field study programs from Homer, around Alaska, and beyond.  At the Center for Alaskan Coastal Studies (CACS), one of the highlights of my job is guiding youth and adults into the intertidal zone to explore the amazing biodiversity that exists there.

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A 4th grade student from West Homer Elementary explores a tidepool in Kachemak Bay

In my lifetime as a Homer resident, and over the past 12 years as an educator in Kachemak Bay, I have witnessed seemingly unfathomable changes in the Bay’s ecosystems.  These changes have been concerning to all of us who live here and are sustained by Kachemak Bay.  Most recently, we watched as many species of sea stars succumbed to sea star wasting syndrome, their bodies deteriorating and falling apart in the intertidal zone. By fall of 2016, only leather stars (Dermasterias imbricata) seemed to remain.  But over the past year, we’ve watched as true stars (Evasterias troschelii), blood stars (Henricia spp.), little six-rayed stars (Leptasterias spp.), and others have begun to reappear in the tidepools.

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Tidepooling in Kachemak Bay, this 4th grader found a healthy, large adult true star!

This past week, I was lucky enough to be the naturalist educator for students from West Homer Elementary as they spent 3 days in a remote part of Kachemak Bay.  This was particularly poignant for me, as many of my most treasured memories from my own elementary school experience come from a similar field trip with CACS in 4th grade.   That trip helped to inspire me towards a life of curiosity and wonder, passion for science and teaching, and commitment to stewardship of ecosystem and community.

So it was even more special that on this trip we observed a wonderfully diverse array of sea star species, including over a dozen sunflower stars (Pycnopodia helianthoides). I’ve only seen a couple of these magnificent sea stars since they all-but disappeared from Kachemak Bay in August 2016, leaving behind only eery piles of white goo.  Their absence hurt my heart, and the potential impacts of losing this important predator reverberated in my brain.  Though the future of these stars remains unknown, it was such a joy and relief to see a good number of apparently healthy sunflower stars in the intertidal this week!

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Finally, a healthy, good-sized sunflower star!

The Northern Gulf of Alaska Long-Term Ecological Research (LTER) site was created, in part, to develop an understanding of the response and resiliency of the Northern Gulf of Alaska to climate variability.  In a time when people, young and old, across Alaska and beyond are increasingly concerned about impacts of climate change, it can be challenging for educators to get youth involved in ways that aren’t overwhelming, saddening, or frustrating.  Part of my work at CACS has been thinking and working with teachers, community educators, and researchers about how we can engage youth in ways that are realistic but hopeful and proactive.  The idea that I’ll be learning about not just climate impacts but the potential resiliency of the Northern Gulf of Alaska is so cool!  I’m excited to find out more about the unique species, life cycles, and natural histories that make the Gulf of Alaska such a good place to study ecosystem resiliency, and I’m inspired to learn more about other ecosystems close to Kachemak Bay and their own potential resilience.

I am really looking forward to my time on R/V Tiglax in the Gulf of Alaska!

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A day kayaking with my partner Nathan and his 6-year old daughter, Johanna. I love spending time on the water, and am excited to get out in the Gulf on a much larger vessel!