[Presenter] This conference will now be recorded.

All right, well, good morning, everyone, and welcome to another EcoFOCI Seminar Series. I'm Deana Crouser, co-lead of the seminar series with Heather Tabisola. This seminar is part of NOAA's EcoFOCI biannual seminar series focused on the ecosystems of the North Pacific Ocean, Bering Sea, and US Arctic to improve understanding of ecosystem dynamics and applications of that understanding to the management of living marine resources. Since 1986, the seminar has provided an opportunity for research scientists and practitioners to meet, present, and provoke conversation on subjects pertaining to fisheries, oceanography, or regional issues in Alaska marine ecosystems. Visit the EcoFOCI web page for more information at ecofoci.noaa.gov. We sincerely thank you for joining us today as we conduct our all virtual series. Look for our speaker lineup via the OneNOAA seminar series and on the NOAA PMEL calendar of events. And if you've missed a seminar, you can catchup on PMEL's YouTube page. It takes a few weeks to get these posted, but all seminars will be uploaded and posted soon. Please check that your microphones are muted and that you're not using video. During the talk, please feel free to type your questions into the chat. I'll be monitoring the questions, and we will address these at the end of the three talks. And today, I am pleased to introduce Dr. David Kimmel. Dave is the lead research oceanographer for the zooplankton team in support of NOAA's Alaska Fisheries Science Center. He received his PhD in Marine-Estuarine-Environmental Science from the University of Maryland. And his research experience, or expertise is in biological oceanography, zooplankton ecology, coastal ecology, climate impacts on ecosystems, and quantitative ecology. And with that, let's begin.

Thank you, Deana. I'm assuming everyone can hear me. So if not, please let me know, 'cause all I can see is the screen.

We can hear and see you great.

Okay, perfect. All right, let me see if this advances the slides. So far, no luck. Hmm. Do you guys know what, why it won't advance? There.

[Deana] There we go.

All right. Must've been that, maybe it's that mouse change thing. Okay. All right. All right, let's give it a shot. All right, I'm gonna talk to you today about the zooplankton community in the north Bering Sea and how it is responding to different contrasting warm and cold periods. And the first thing I wanna do, yeah, I think it's the mouse thing. When I go to that, it doesn't allow me to, there we we go, all right. So first, I wanna acknowledge some folks. My co-authors on this manuscript are Lisa Eisner and Alexei Pinchuk, and they've had a lot of input onto this to understand the research that I'm gonna show you today. And I also wanna thank EMA staff, because a lot of what you're gonna see today is coming from their survey in the north Bering Sea, and so there's a lot of folks I've listed here that participate in that survey. And I wanna especially acknowledge Ed Farley, who's the one that asked me to sorta work up these data. If I didn't list your name here, I apologize, but this is from the last report I saw. And all those folks are instrumental in getting these data and increasing our understanding of the dynamics. And because this happened over many years, there's lots of folks that worked to sort the plankton and identify them. UAF staff, TINRO staff, the Porting, the Poland Sorting Center I wanna thank all those. And as well as the Zooplankton Team: Kimberly Bahl, make sure our data's good, and Deana, Colleen and Jesse are critical to the functioning of the Zooplankton Team and making sure that these data are usable and ready and available. So I just wanna thank everyone before I get started. All right, so what am I gonna talk about today? Well, today I'm gonna give you a little bit of an introduction into the topic. I'm gonna talk about the objectives of this particular set of research. I'll give a little bit on the approach. I won't go into all the statistical detail, but I'll give you an overview of what I did and the results in some of my conclusions in future work. And so this is coming on the heels of going out to sea in COVID and I had a really good time washing down the nets, as I always do, but my favorite thing to do is to scrape barnacles off orrels, and this is my masterpiece. So I'm looking forward to heading back out on the spring mooring cruise and getting at this again. Today, I wanna talk to you about zooplankton. And I like to call zooplankton charismatic microfauna. They're the most abundant multicellular animals on earth. In fact, there's more multicellular animals that are copepods than anything else on the planet. So they're very important. They are the fulcrum of aquatic food webs. They sit right in the sweet spot between the primary producers and those of the higher trophic levels. And so they're funneling carbon up to fish and higher trophic level organisms through both the microbial loop as well as the classic food chain that starts with phytoplankton. So they play a very important role as the gateway of carbon to higher trophic levels. They play a really large role in carbon flux in the global ocean. So what you're looking at on the right there is zooplankton poop. And this poop is packaged by a lot of zooplankton so that it sinks rapidly. And so there's a lot of carbon flux that's going on in the ocean related to the behavior and the ecology of zooplankton and so it's important to understand their dynamics. And they're really excellent organisms to study climate effects. And so what you're looking at on the right there is some data from the Continuous Plankton Recorder, which has been going since the '50s to show that if you monitor these organisms, they're responding to climate change in, over the course of long data records. And so they're really good organisms because they're not fished, so there's no direct human influence. And I say well, mostly because there are some targeted fisheries for euphausiids, for example. And they have short generation times. So if you have an event or a heat wave or something occurring in the system, they often respond. And that response is then cascading up the food web. And so it's a very good group of organisms to study, to get at some of the changes we see in the environment. And in the Bering Sea, they're also very important. And so on the left, you see a food web diagram from Aydin and Mueter paper from 2007. I'll just highlight the right side here, and that's, you're looking at, the red is the pelagic food web, blue being the benthic. And you can see euphausiids and copepods, again, right in that sweet spot, sitting above the phytoplankton and below the major consumers, like walleye pollock that we're interested in. And so obviously we have a very strong interest in studying what happens with these zooplankton as they relate to walleye pollock as a commercially fished organism, big industry, but they also are feeding things like seabirds. Many seabirds rely heavily on zooplankton as a major prey item. And then on the bottom there is the critically endangered North Pacific right whale that targets Calanus, directly as its major prey item. And shout out to Jessica Krantz for spotting a few of these whales last summer and looking forward to seeing, if we can see some more on the upcoming cruise. So that's a humpback. Well, the internet is lying. Anyway, so zooplankton dynamics in the southeastern Bering Sea have long been studied. And there's a paradigm that's kind of emerged between these warm and cold periods that I've highlighted here, as warm in the red and cool in the blue, that when we have these periods, Calanus glacialis tends to accumulate. When we get in these cold periods, we see an increase in the population of this organism. And you can see, it's kind of an important organism 'cause it's got this little fat globule inside it. So these organisms are accumulators of lipids in the environment. And therefore, they're a really nice juicy prey item for fish. However, when we get warm periods in the southeastern Bering Sea, the populations of this organism tend to decline on average. So we tend to see an increase in cold periods, decline in warm periods. If we look at a smaller copepod like Pseudocalanus, which is roughly half the size of Calanus and does store a little bit of lipid but not nearly as much, which we'll talk about later. We see that during the warm periods, at least historically, they weren't particularly high. They had some little bit of decline in the cold periods. And then in this recent warm patch, we've seen a really strong increase in the abundance of these smaller copepods, like Pseudocalanus, and there's a few others that we'll talk about. So what is the effect of all this? Well, the paradigm that came down was the Oscillating Control Hypothesis and that has been sorta worked on over the years. And the fundamental understanding is that when you have a late ice retreat, you tend to get an ice associated algal bloom and this transfers a lot of carbon and lipids directly to Calanus, which it uses for its reproduction. And so over the course of the year, this Calanus population, due to the colder temperatures and lower metabolic demands, tends to accumulate. And so late in the year, it's available as a prey item for walleye pollock. However, if you have an early ice retreat, you tend to get a delayed spring bloom and it's made up of smaller cells. And the increased temperatures increase the metabolic rate and this is really favorable for small copepods in the sense that they can turn over their populations faster and accumulate biomass. And the higher metabolic rate is unfavorable for Calanus and this leads them to be in low numbers later in the year, either through diapause or predation effects, we're not entirely sure which. But this is the situation that is happening in the southeastern Bering Sea, or at least what is our understanding. And this is important for walleye pollock, because if you look on the left, years that are warm, the walleye pollock tend to have much lower lipids in their diet. And that's because Calanus isn't around. And then as you get into the colder periods, the amount of lipid in their diet increases. And that leads to relative difference in the energy density of these fish. And so this work by Ron Heintz in the bottom left here, you see, during the warm periods, the energy density is low in these fish; and then as you go into the cold period, that energy density increases. And the hypothesis is that that's linked to overwinter survival. In other words, if they're able to lay on more lipids, they're able to survive. And the work of Ellen and Lisa Eisner has shown that if you actually look at the large copepod abundance, and that's primarily Calanus, you can predict what the age-3 pollock biomass will be in three years. So there's a strong link mechanistically between a good Calanus population year and a good year for walleye pollock. And so that's what's going on in the southeastern Bering Sea. What's going on in the northern Bering Sea? Well, there's also been some studies there. We've been monitoring populations, but we don't get up to the northern Bering Sea with as much frequency. And so there's not as long a time-series to look at these sort of things. And so Lisa Eisner has done some work over here in the left. And you can see what's happening is that when you have a warm period, and the triangles here are small copepods, larger the squares, and you got warm down here, cold. When you have this warm period, you tend to get a little bump in the abundance of small copepods. But there's not a huge difference between large and small copepods and very limited difference in their biomass. And a figure that I did for one of Phyllis' papers is looking at the abundance of Calanus. And you can see, as the C5s go along over time, this is the C5 stage, the one before adult that accumulates lipids, not a lot of change in their population. But when we got a warm period later in the early two, or early teens here, the number of stages, of earlier stages decline and that's 'cause the warmer temperatures made them develop faster and they turned into C5s, but the overall abundance of that doesn't look like it was varying all that much in terms of total numbers. So the hypothesis was that there is a zooplankton population in the northern Bering Sea that's not super variable because there isn't as much influence of retreating in accumulating ice year-to-year, all right? Then came the winter of our discontent or the winters of our discontent. And that's when we had a massive shift in sea ice in the Bering Sea. And this is looking at total ice extent in the Bering Sea. You're looking at the total median amount here over time and then the range. And then the winters of '17 and '18 you can see are, it started out at least '18 and '19 within the median range but both of them wound up by early in the year having a very low ice extent. So this was not predicted to occur north of 60, this was something that was predicted to be a rare event. In other words, the northern Bering Sea would stay sort of cold and dark until this event happened. And Phyllis and Shaun Bell published a very nice paper showing these ice extents and how minimal the ice was in '18 and '19 compared to prior years, like the cold year of 2012 or the extent of 2003. And that ice that was lacking led to a severe reduction in the cold pool. So we can see the cold pool extent for these cold years '12 is much reduced compared to a warm year like 2003, and then 2018 essentially had extremely limited cold pool. So this event was sort of precipitating and we wanted to find out what was happening in the north Bering Sea. And so what the ecosystem was doing is there started to be some interesting responses going on. The first one I'll highlight is on the left, a work by Duane Stevenson and Lauth, that shows that in a normal cold year you've got a lot of walleye pollock and Pacific cods sorta spread out in the south Bering Sea and out on the shelf break. And during that first warm winter when there wasn't large ice extent, the walleye pollock and the Pacific cod went north. And they're not normally found there. So this was a big response. And the other thing that happened is we began to see some bird die-offs. And a really nice paper by Piatt shows that these birds appear to be caught in this ectothermic vise whereby warm water increases, metabolism reduces prey quality of things like forage fish, and you see the little zooplankton down here that we're gonna talk about, and it also increases the competition and metabolic demand of groundfish and the birds are squeezed in between. So we started to see these events happening, bird die-offs, movement of fish. And so the question became: What's going on with the zooplankton? So my goal in this particular project was to develop a time-series of zooplankton abundance in the northern sea from some different data sources and then determine if the north Bering Sea shows a similar dynamics to the southeastern. Is it that warm/cold dynamic that we saw in the southeastern Bering Sea? Or, basing it in on... [dog toy quacks] oh my god, he's chewing a toy. Stop that, dog, sorry. Is to determine if all warm periods are alike or is each, excuse me. Dog! Oh, sorry. Thank you. You don't get that when you're giving a seminar in person. Okay, "Are all warm periods alike or is each warm period unhappy in its own way," after the work of Tolstoy in 1878. And so we wanna explore the consequences of these, if there is a shifting zooplankton community dynamics in the north Bering Sea, what's going on with that? So those were the objectives that I started with. So the first thing we had to do was to build the time-series. And this was brought to me by Ed. And he said, "We've got all this zooplankton data, can you help us make sense of this?" And so they have a salmon survey that goes on in the inner shelf of the north Bering Sea that's been going on for quite some time. And so that was the first data set. And then we had some EcoFOCI surveys. And so we were able to limit these to late summer, August, September, and into this region here, sort of, we had a middle shelf portion and an inner shelf portion. And if you look at the actual data distribution, you can see over time that we consistently sample this spatial area. And we do miss the outer, the middle shelf a little bit, but we have a consistent temporal and spatial area where we can accumulate data to look at a time-series from the northern Bering Sea. So that was the first thing that we had to do to put this data set together. The second thing was we had a lot of different surveys. So we had some different methods. Early on for the small zooplankton, we, there was the use of a Juday net, which is a vertically towed net of small mesh size. And later on, there was a Bongo array that had small mesh size going on that's towed and there was a large net that was consistent throughout the time-series. So we had to sorta figure out how to compare these data. And that was sort of my job, was to tidy these data sets, get them together. And this is probably not an accurate picture, but at sometimes frustrating to get these data sets to talk to each other. And this was before I had my OpenScapes training, so I wasn't quite aware of all the methods to get this done a little bit more efficiently. So the first thing I did is I got lucky in that when we went out in 2017 as part of the Arctic IARPC survey, the Juday and the Bongo nets were deployed at the exact same time. So I had about 30 or 40 or more stations where the Bongo and the Juday network were sampled at the same time. So I did a comparison. And what you see is, looking at two small copepods here that I would be interested in developing a time-series for, that the two gears match up pretty well. And also, if you look over on the right here and you see the abundance as you move station by station. When one net goes up, the other one goes up. And when one net goes down, the other one goes down. So they are describing the variability going on here in a similar manner. So we felt that we could put these gears together and develop this time-series with the caveat that there might be some gear differences that might explain some of the variability. So the way to get around that is to use an anomaly approach, which I'll talk about in just a second. And so my workflow for this particular analysis was to look at a bunch of environmental covariates. So establish the zooplankton time-series, look at some environmental covariates that might be impacting the zooplankton population, like climate indices, ice, wind, salinity, temperature, the usual suspects. And then describe the warm and cold dynamics in the north Bering Sea. And use an anomaly time-series so that we can standardize the data by the long-term mean. And then look at the differences in the anomalies of the different covariates. And then look at a multivariate redundancy analysis, which allows us to put all of the environmental and all of the zooplankton data into the same analysis and then figure out how the assemblage, the zooplankton assemblage itself is responding to any changes in the warm and cool period. And then at the end, we can look at the individual zooplankton, look at their anomaly time-series and see how are these individual species of interest responding and that would be a way to determine what the overall effect of these individual attacks are that might be important in fish or seabird or other animal diets. So that was the approach. The first thing we looked at was ice area and the cold pool extent. And this, of course, is looking at these anomalies in ice area for the entire Bering Sea. And the March ice cover at M8. And you can see it follows along this pattern, where we started out with these warm years, '02 to '05, and then colder years, and then another warm period, and then that dramatic drop off of ice in '17 and '18. And it's really quite pronounced in the cold pool area where you see there's negative anomaly, so reduced cold pool during this first warm period, increased cold pool area in the second warm, the cold period, and then reduced cold pool area in the second warm period. So throughout the talk, I'm gonna refer to this first warm period as warm period 1, the second is cold, the cold period is just one cold period, and then the warm 2 as the second warm period. So this is gonna be so how I'm framing the rest of the results. And so when we looked at annual indices, the annual climate indices, we looked at the Arctic oscillation and the North Pacific Index, we found no major differences. And these plots are gonna be box plots. So I'm plotting all the data. There's a median line here in the center and then this is the interquartile range, and then some tails on these boxes that show the full extent of the data. And then I statistically compared these different warm and cold periods, but I'm gonna ignore that for the moment just to show you that there wasn't, there was an increase in the Arctic oscillation during the second warm period, but there was no statistical difference between these. And the same thing for the wind. We look at the different wind speed coming from these directions in the area during spring and summer and we didn't see any major statistical differences in these winds. And that's not surprising. When you average wind over this longer time period, you don't tend to see a lot of differences in the wind even though wind played a very important role in the development of the ice, that ice extent in the years, as it was explained in Phyllis' paper. Where we did start to see the differences, of course, is in temperature and salinity. And so I'll just point out that on the middle and inner shelf we have different sets of measurements from the FastCAT and CTDs. And you'll see that in the second warm period, it was pretty warm. It was definitely very warm at the surface, and this was statistically different from the other years. Also, you'll notice on the bottom temperature, on the middle shelf, it was very cold, warmer here, but due to mixing that there's a lot of similar temperatures throughout the water column on the inner shelf. And again, for this, the salinity, we can see that there's elevated salinities out on the middle shelf, but we don't see this impact on the inner shelf. And I'll talk about how these warm periods and cold periods differ in just a second. But one of the major differences we saw was in chlorophyll A. And so if you look at the first warm period to the second warm period, we see a sequential decline in the amount of total chlorophyll we measured in this region and particularly in the number of, or the abundance of chlorophyll A cells that were greater than 10 microns. And so these are the larger chlorophyll or larger phytoplankton cells, and these are declining at their lowest level in the second warm period. This was much more pronounced on the middle shelf than it was on the inner shelf, but there was a definite trend downward. And so if we summarize sort of the environmental differences, we didn't see much difference between these time periods in terms of annual climate indices or average winds, but the two warm periods were different in terms of how they behaved. In the first warm period, there was a small reduction in ice area but a really large one in the second warm period, particularly in those latter years. The cold pool was reduced during the first warm period. It was a pretty large reduction overall. And the second warm period it was started out small and then it had a major large reduction towards the end. In the surface temperature, it was similar to the cold period on the middle and inner shelf in the first warm period but much higher in the second. So it seemed like the surface temperature responded more strongly, then the second warm period. But the bottom temperature responded only, it was similar to the warm one period in both regions and it was highest on the middle shelf during the first warm period. The surface salinity was highest on the middle shelf, lowest on the inner. And you could think about the effect of melting and input of freshwater on the inner shelf that's being mixed, lowering that surface salinity. And then the chlorophyll itself was highest in both regions during the first warm period, and also this had the highest proportion of larger cells and it was the lowest in the second warm period. So this sorta sets the stage for us to go talk about the zooplankton. And I'll first start with the multivariate work. This is a redundancy analysis. There's a lot going on here, so let me walk you through this. The first thing I want you to know is that the first warm period are triangles. The second warm period are the squares and the circles are the cold period. And what you're plotting here, these are all different zooplankton species. And I'm not showing the environmental part of this matrix because you wouldn't be able to see much of anything. But what I want you to takeaway from this is first notice on the outer shelf that, and, or I'm sorry, on the middle shelf in both regions, the cold period, the cold information is on the left. So things like heating mass and Calanus, they're going towards the cold. Whereas this large chunk of species is responding strongly to this warming. And not only are they responding to this warming, they're doing it much more in the second warm period and that's due to the spread of these squares being much wider on both of these things than the total spread of the triangles. So whatever was happening in the second warm period we saw a major response going on out of the ecosystem, okay? And so let's dig into this a little bit more deeply and let's look at the individual species and some of their anomalies. So if we look at zooplankton that are cold associated, like Calanus glacialis, we see the same dynamics that we saw in the southeastern Bering Sea, especially on the middle shelf where we tend to see Calanus, which is not as abundant on the inner shelf. So we see negative anomalies in the warm period, particularly in this late one, and then positive anomalies in the cold period. And that's less pronounced on the inner shelf except in the cold period. And Lisa has shown in her papers when you get a really strong cold period, you tend to get an intrusion of this middle shelf community onto the inner shelf, hence the anomalies. But most of the time, we don't see a lot of Calanus in this particular area. Parasagitta, on the other hand, is arrowworm, shows very similar dynamics. This is a predator that's probably chomping down on Calanus. And so again, it's showing negative anomalies during these warm periods and positive anomalies during the cold period, right? But then it got interesting. When we went to warm associated copepods, the thing that we noticed the most was was in these two broader groups, that I call small copepods, which are these small neritic copepods that are much smaller than Calanus, continuously reproducing species. There's a couple different species in there, like Acartia, Centropages, Tortanus, a lot of these smaller, more neritic copepods. And then meroplankton, which are found only in the plankton for a short time, but they're larvae, things like bivalves, clams, polychaete worms things of that nature. And normally you would find those associated with the inner shelf because it's closer to the bottom. And when those adults are releasing their larvae to spawn, you would see them in the plankton. And what we found is that for these small copepods, there were massive positive anomalies on the middle shelf, particularly in '17 and '18. And they were so high that they sorta swamped the variability that was going on in the rest of the data set. And it was also the same for meroplankton. So when we got these warm periods on the middle shelf, we tend to see an increase in this taxa. It wasn't as pronounced on the middle shelf, 'cause these guys are normally found there, but you still see the positive anomalies here. And for meroplankton, it really wasn't as big a response as it was out here on the outer shelf. And these are big anomalies. We're talking about two to three standard deviations off the long-term means. So very interesting. If we dig into that a little bit deeper into some of the actual taxo, like Pseudocalanus on the top here, again, we see that same response: very strong, positive anomalies out on the middle shelf; strong, positive anomalies on the inner shelf particularly during that second warm period. And same for Polychaeta, except Polychaeta is having that strong response on the middle shelf but not as much on the inner because we would expect them to sort of be there most of the time. The weirdest thing that we noticed was the massive increase in the abundance of this copepod Epilabidocera longipedata, which is a very interesting copepod that not much is known about it, it's blue, and that's because it's neustonic. It sorta sits at the surface, it has this bluish color, and I think that's related to the fact that it's exposed to high UV radiation so it's got some sort of pigmentation to help with that. But normally, these guys are rare. You find one or two per meter cubed. But in that last year, 2018, these guys exploded. And I was talking to Alexei Pinchuk, he sees the same thing on their cruises that they've done, where these guys are showing up massively in juvenile salmon diets and we have no idea much about their ecology or what's causing the ecosystem to do this. So to summarize the zooplankton response, the cold conditions tend to favor this population size increase in Calanus and Chaetognaths, sort of like we saw in the southeast Bering. But the small copepods and meroplankton increased greatly during the second warm period, and they didn't show that much of a response to the minimal first warm period, or, I mean, they showed a minimal response to the first warm period. And that response seemed to be the greatest on the middle shelf. So these small guys and this meroplankton that aren't normally found on the middle shelf seem to be in that area and in high numbers. And at least one copepod species, this Epilabidocera, increased tenfold in numbers, which was very surprising. We did not expect to see that. So I'd like to work through a little bit of, say, what happened, my working hypothesis, and I'd love to hear everybody's thoughts on this. But the first thing is, is obviously ice was the major thing that changed. I don't think there's any debate about that. But the difference between the first warm period and the second was the first one ice was below average, but it was within the historical range and it stuck around longer. So even though there was sort of this limited extent with ice, it was within the historical range; and even though it was low, it stuck around longer. And that was not the case in the latter warm period, where ice was far below average and retreated early. And so that means the northern Bering Sea got warmer than ever before. As we saw in our surface temperatures, the warm water was really warm. And I'll show you in a second that it was widespread, this warmth. And this is a data from Phyllis and Shaun's paper to show M5 and M8 long-term mean from '05 to '17, and just showing in the '17, '18 winter how much it warmed up at the bottom. And so the cold pool sitting here at the two degree and by April and May of 2018, we were in excess of that. So there was a very strong warming and it lasted for a long time over the north Bering Sea. The extent was widespread. So these are bottom trial temperatures that were published in Lisa Eisner's 2020 paper. And you can see the wide extent of these very warm temperatures spread. And here's our study area here. You see minimal cold pool widespread warming waters out into this area and into the middle shelf that was going on during these years. Well, why is that important? Well, as I said before, I sort of alluded to this, but the zooplankton community is divided into three different domains: and we know there's a coastal domain that's associated with certain species, a middle domain that's associated with certain species, and an outer domain. And this is great historical work. This is an old paper from '82, but it's a goodie. And it shows as you move here closer to the shelf, to the outer shelf, you see these small copepods, like Acartia and Pseudocalanus, are found in the inner shelf. And then as we move to the middle shelf, we see increased abundance of Calanus and Metridia. And then as we move to the outer shelf, we see these larger copepods like Calanus cristatus, which is now Neocalanus, that genus has been split. Plumchrus are larger copepods that are out on the outer shell. So you can probably think about where I'm going with this, that during 2010, when it's really cold, there's ice, there's a late retreat that creates a cold pool and that really squeezes the neritic zooplankton community near the coast. They're restricted in scope and they have little time to accumulate abundance in the north Bering Sea because there's a lot of ice, it retreats late, and they don't really have those warmer temperatures to get cranking in terms of increasing their population sizes. In the second warm period, there was very little ice, early ice retreat, which eliminated the cold pool almost entirely. The neritic community then had time to sorta spread onto the inner shelf, there's lots of warm temperatures, lots of time to accumulate abundance, and that's favorable for these fast, small reproducing species. So that's the working hypothesis of what happened. And the consequences of that are that when you warm the system, you tend to have an impact on not only the community size, but also the individual taxa that are making up the zooplankton community. So what I have on the left here is a picture of some different copepod species. I've got Calanus hyperboreus, which is a central Arctic Basin species, it's huge. It's about seven or eight millimeters as adults. And you can see it has a huge, nice fat lipid sack in it. For comparison, there's Calanus glacialis, which is our Calanus that we find in the Bering Sea. You could see it also, it has a nice lipid sack. And then we go down to something like Metridia, which was that sort of middle shelf species I mentioned before. I had to draw in a Pseudocalanus, roughly I grant you, and put it in there, it's roughly sort of in between Calanus and this smaller copepod of Oithona. Over here we can stage CV dry mass, that's milligrams of individuals, milligrams per individual, and then we can also look at things like their percent lipid. And if we look at Calanus as being our equivalent, so how many copepods does it take to equal one Calanus? You need to eat 0.4 of a hyperboreus, but 17 Metridia, 73 Pseudocalanus, and over 680 Oithona. And even more important, is that 65% of these copepods, 60% are lipid. So not only are they good in terms of their individual dry mass, they're also, what I call, why I got a piece of bacon down here, one piece of bacon has 54 calories, 65% of which come from fat. So I think these are the bacon of the north Bering Sea or the Bering Sea. And these large copepods have about 20 to 30% of this oil sack volume versus their overall volume is in lipid. Whereas the small copepods, even though Pseudocalanus does hold lipid, it often has less than 1% of its oil sack volume to prosome ratio in lipid. So not only do you get a shift in the total individuals that are there, but you get a shift in their overall biochemistry and the amount of carbon that they're able to transfer to higher trophic levels, right? And so is this a problem? Somebody has actually proposed that there might be a mechanism of resilience. And this is a paper by Renaud. And what they're arguing is that, okay, even if it does get warmer, the body size of the copepods is gonna decline and the total amount of lipid per individual is gonna decline, but we might also see an increase in the population turnover rate and that might mean we're producing lipids at a higher rate that might compensate for this lack of Calanus. I happened to not subscribe to this. I really think the packaging of the Calanus and the amount of lipid that they have and the fact that fish have evolved to take advantage of that, of that dietary availability late in the year cannot be compensated for by switching to smaller sized copepods even if they do produce a lot more lipid over the course of the year. So we'll see what happens over time, but this is an interesting hypothesis that there might be a mechanism of resilience. So what I wanna do in the future is I'd like to look at some cross-trophic level integration, and we're gonna do this by looking at the overall food web, so start working on the Arctic IARP data and other things and look at how the smaller trophic level organisms like the phytoplankton and the zooplankton are interacting to act as carbon gateways if the system is changing in terms of benthic-pelagic coupling or warming or organism size. I definitely wanna look at the lipid and fatty acid profile. So Louise Copeman's been leading that work. And we definitely wanna compare these and see how the lipids and fatty acids are doing. But my real passion is looking at trying to increase our capability of imaging technology to increase our monitoring and understanding of zooplankton populations. What I've shown you today is really a snapshot of what's going on in the system. I don't know what these populations are doing over the long term and I'd really like to increase that monitoring, so we've been working on institute imaging technology and algorithms to identify zooplankton, and I've got a lot of partners to do that. And I'm hoping that we make some breakthroughs this year in the application of this technology. And I would be remiss if I didn't acknowledge something I've ignored throughout the entire talk, which is euphausiids, which are really, really important. But our methods for sampling euphausiids are poor. The Bongo net doesn't do a really good job of estimating them. And so we're looking to increase the euphausiid monitoring this summer with some Methot sampling. We wanted to do this back in 2018, but of course we've had sorta issues getting out to sea. So that's my future work. And I wanna thank you for your attention. And I'd like to tell you that this goal is an article on a peer-reviewed journal. I'm waiting on one internal reviewer to get this out the door. So in the meantime, I've been whispering into a hole in an enchanted oak in my backyard, which is, has been therapeutic, but my aspiration is to definitely have a Broadway musical in the vein of Hamilton so I can retire and devote all my time to writing musicals about planktons. So thank you very much for your attention and I'll be happy to try to address any questions. Thank you.

Thank you, Dave. I really am behind the plankton musical. [laughs] I support you in this effort. Anyway, thank you. I'm gonna give you a round applause. Thank you for your talk and all of your wonderful jokes aside. Deanna, if you wanna pop on as well, you may. Like to take this time and open it up to questions. NOAA recently has a new policy. So if you pop on questions with video, you'll have to sign a form. Otherwise, just go ahead and ping it in the chat if you don't wanna sign a form.

Wait, what?

Yeah, it's a new privacy policy. You'll have to sign it too if we put these up on the internet now. So Deanna and I have to sign them as well. We haven't done that yet. Or I have an old one that maybe I did last year. Yeah, they require now any videos, if you appear on them and they are recorded, you know have to sign a waiver essentially. Libby, good morning. Libby says, "Interesting. What might be the mechanism for the stronger chlorophyll A, chlorophyll response in warm period two?"

Oh yeah, good question. So I have two points there. The first is that Jeanette Gantz's working on a very nice paper to look into that, looking at the differences in the chlorophyll box, in terms of the size to see how that's related to the ecosystem. So stay tuned for that. Point 2 is that, generally, when you get warming, one of the universal ecosystem responses is to decrease size. And that response is pretty strong in unicellular organisms in particular. So if you were to warm a mesocosm, one of the first things that happens is the cell size of the phytoplankton gets smaller. And that's been noted throughout the global ocean in the Arctic. And so that could be the mechanism that's driving those down. If it's prolonged warming, that just creates a situation whereby cell size is smaller. So that's my current understanding of it, but it could be something else.

Thanks, Dave. Libby says, "Thanks and looking forward to the musical." [laughs] I'm really fond of the fun work, we got you. Shaun. Good morning, Shaun. It starts off, "So lots of ice this year, down all the way to M2 at one point. What are you expecting, Dave, you might see on your much hyped and loved spring cruise?"

Ah, yeah. So what I'm expecting is I would think that this year we're gonna see what we saw last year, which is a fair bit of Calanus and Chaetognaths hanging around. Typically, during a year when we have a lot of ice, that's what we see. We sorta things not really cranked up just yet. We see the Calanus that have come up to reproduce and then their early life stages sort of getting a shot to start and then Chaetognaths trying to chomp down on those Calanus that came up early, early in the year. So that's what I would expect to see, sort of similar to what we saw last year. But who knows? Every year is something different. So I think that's what I would expect.

Thanks for that, Dave. And thank you, Shaun, for the question. Al is here this morning and he asked, "Could you comment on top-down effects? That is how much of the decrease in fatty zooplankton and warm weather is due to increased grazing by fish, lose metabolism, goes up in the warmer conditions."

Yeah, so I think the change in population size might definitely be related to some top-down effects. But the other thing to note is that when we do look at these copepods during the warm period, they tend to be smaller. And so even in a warm period, Calanus size will reduce. And so the amount of fat that they carry in them is reduced so I think the warm weather is definitely causing that in terms of their size, changing their ability to accumulate fat. And so if you look at a copepod that you capture that's not grazed, you see less fat in it. But I don't think the overall accumulation of fat has much to do with the actual grazing. I don't think, I think it's more top or bottom up driven by the grazing that they're doing on the zooplankton, or phytoplankton and microzooplankton committee, I'm sorry, microzooplankton community rather than grazing. Because I think grazing would just remove individuals from the population, but not necessarily affect their fat accumulation.

Any follow-up to that, Al?

[Al] No, thanks. That's a good explanation.

Thanks.

And Mary Beth Decker also says great talk and has suggested some musical titles for you.

Hmm. Aridification. I like it, Mary Beth. Thank you. [laughs]

All right, any other questions from folks? Dave, I had, oh, okay, Ryan is here, okay. And Cody, all right. Ryan, let's see, "Regarding the interesting blue copepods, are they usually ubiquitous but generally in small numbers, or do they come from offshore or southern latitudes? i.e., is advection from somewhere else an important factor?"

No, I don't think so. I think they're very prevalent. I've caught them in the Gulf of Alaska. I've caught them in the Bering Sea. I think they're endemic to the region, so they're not necessarily being advected from anywhere. They are generally in very small numbers and they are neustonic. So when we were doing some neuston tows, which are just sort of skirting along the surface to look for sablefish, we tend to catch more of these Epilabidoceras. So it could be that the reason Epilabidocera is not well-represented in our data set is because when we're doing an oblique tow we only capture that top little bit of a layer for only a few seconds each time we bring the net in and out. And so that, I think, is the reason that we don't see very high numbers. But we definitely haven't noticed an incredible abundance like this ever. So it's very, very strange. And I don't think that they're, something is happening that whatever competition or whatever situation is happening is releasing them to increase their population sizes. So it's very strange and I would love to look into it more. And Epilabidocera longipedata or amphitrites, both are accepted.

Can you say it three times fast?

Epilabidocera longipedata. [laughs]

I'm not even gonna try [laughs]. I love it. Okay, Yvonne, good morning. Yvonne asks, "Are you planning on adding eDNA studies in addition to computer imaging?"

So right now, I am not working on any eDNA studies. We've taken samples in the past for folks, but we haven't really developed a full scale eDNA project yet. Right now, I'm focused almost entirely on imaging. I've got algorithms for microscopes. Deana has worked tirelessly to develop an algorithm for our in situ camera. So basically we're really heavy into the imaging because we think it might have more immediate applicability. Though, I would be very interested in eDNA, particularly because if it's able to monitor the population better, that would be awesome. But the other is we've got a lot of species issues that we don't go down to the species level, say, with Calanus. We think it's glacialis, it might be marshalli, it might be a mixture of different haplotypes. We've got at least four species of Pseudocalanus that could be out there that we don't identify, and they might have very different ecology in terms of the Arctic species having higher lipid amounts versus the more boreal species that we see or sub-Arctic species. So yeah, we haven't quite got to the eDNA route yet. But I'm not a DNA guy, so.

Couple comments from Kim and Peggy, everybody, myself included, Deana as well. We were talking about this. I appreciate the bacon. What did I call, Deana, the bacon of the northern Bering Sea. Yeah, I like it. It's replaced cheeseburger. Bacon is a much more applicable food.

Yeah, I was quite struck by the fact that 65% of the calories in a piece of bacon come from fat. I feel like I should've learned that at some point earlier in my life. [laughs]

Would it deterred you from eating more?

No. [laughs]

Dan. Good morning, Dan. Dan asked, "Which warm/cold changes that you found, do you think, may represent annual spatial changes in the zoo community in the northern Bering Sea? And which ones may be phenology changes?"

Hey, Dan, that's a really good question. It's one I've sort of struggled with. I think when it comes to phenology, that's the one I think that relates to the larger copepods that are having an annual cycle where they're coming out of diapause and the warming could affect that timing, I believe. There's lots of hypotheses about what causes entry and exit from diapause and one of them is metabolic increase due to warming temperatures burns through their fat reserves and then they come out earlier. Again, that's one of the reasons why I wanna monitor the population over longer time period to see that, okay? Second is I think spatial changes are a huge part of it because once the ice retreats, you get a bit more movement of water. So we could have a movement of these communities moving around and that's causing us, which we are sampling in the same spot, to pick up things that are, have been moved around rather than difference in sort of things in the same spot that are coming up at a different time. So that's a great question. A very, very interesting topic, but it's something that with only a point in time it's very difficult to answer. And I ran into the same problem in the Gulf of Alaska when I tried to argue phenology change. We didn't have enough temporal coverage to do that. So yeah, but great question. I think it's a very important one to figure out what's phenology and what's sort of movement of these communities.

Awesome. Okay, I think we have time for one last question. And Jim has one on here. And Colleen, yes, we 100% agree that bacon at night, that's completely justified. Jim's question is, "My question is similar to Dan's. Do you believe temperature plays a key role in the zooplankton community across domains in the eastern Bering Sea?"

Right, so I think it's interesting. I think that the current sets up most of the domains. So the inner, middle, and outer just have some different dynamics and so they're sort of along these different fronts. What I think temperature does is affects the way those fronts behave. And so the temperature can move the fronts around and it also causes the zooplankton community to undergo different population dynamics because zooplankton biology is so strongly tied to temperature. In other words, even when we look at changes in chlorophyll and other things, temperature is predominant. And so when you warm the system, as copepods are poikilotherms, they respond very strongly. And so I think temperature is playing a role in moving those fronts around, obviously, but also within those fronts, changing the way the community is evolving over the growing season. In other words, the longer it's warmer, more likely you are to have a small zooplankton community that's continuously turning over rather than the colder community that's undergoing a sort of longer time frame of growth in Calanus that's producing that population.

Awesome. Thank you, Dave.

Well, thank you, everyone. I really appreciate the questions. Great.

All right. With that, we will conclude seminar this morning. Dave, thank you for, with such an awesome presentation and being our first speaker of the series for this spring season. And we will be back here next week, Wednesday, same time, same link. We'll see you all then.