Talking with Kathy, Yosty learned that the common murres in the Gulf of Alaska were starving during this period of uncharacteristically warm water. This common murre die-off event was very puzzling for scientists because there was not a clear reason as to why the birds were behaving abnormally. If the birds were not getting enough food, there must be something in the Gulf of Alaska impacting the food chain.
Scientists study all levels of marine food webs, beginning with the organisms at the base — the plankton. Plankton are a diverse group of living organisms that spend at least part of their life floating through the water column, unable to swim against the current. Plankton consist of both plants and animals and help to form the base of the marine food chain.
Every organism that relies on the ocean for food depends on an adequate supply of plankton to keep the ecosystem properly fed. Even animals that don’t eat plankton themselves, like the common murres, require enough healthy plankton to feed the fish and invertebrates that they prey upon. So, if the common murres were starving, causing them to move close to shore and inland to search for food, and dying in large numbers, there might be some evidence that maybe something was different about the amount or types of plankton in the Gulf of Alaska those years.
Following this lead, Yosty moves forward in the investigation by questioning Gulf Watch scientist Sonia Batten, who specializes in monitoring plankton populations to understand what had been happening at the base of the Gulf’s food chain that might have been related to the murre die-off.
Watch the video below to hear what Sonia has observed with the plankton in the Gulf of Alaska.
VIDEO: Sonia Batten and Plankton
Sonia Batten describes her observations of plankton in the Gulf of Alaska. (4:17)
Narrator: Hmm… It all seemed to go back to the murres’ food chain. Why did these seabirds starve to death? Was something wrong with their food source? Yosty needed to start at the bottom of the food chain. She needed to talk to Sonia Batten, A Gulf Watch scientist monitoring plankton in the Gulf of Alaska.
Yosty: Hi Sonia, what evidence do you have that 2014-2015 were unusual times for plankton in the Gulf of Alaska?
Sonia: We’ve been looking at plankton in the northern Gulf of Alaska since 2000, so we have quite a long time series now. We look at the plankton from spring through fall of each year. We noticed in 2014 and then again in 2015 that there was something unusual happening, and we were kind of expecting it because we knew that the waters offshore were really warm from the end of 2013 through the next two years (really unusually warm, and it’s been called “the blob” by some people). So we were expecting to see something unusual.
What we typically see in the plankton… There are two types of plankton. There’s the plant plankton and those are little tiny single-celled plants that float around and take the sun’s energy to grow – and they typically get blooms of those in the spring because there’s lots more sunlight in the spring, there’s lots of nutrients from the winter storms that have been mixed up, and it starts warming up. All those things are really good for them to grow, so we typically see those take off in the spring. And then as they grow they get eaten by the animal plankton and their numbers die back a little and they run out of nutrients and so on, so there’s lower levels of them through the summer. And then sometimes in the autumn we get another bloom because we get a few storms come in and mix things up again and give them more nutrients. That’s the typical pattern.
What we saw in 2014 was we didn’t see anywhere near as many of those plant plankton as normal, and we saw big numbers of very small animal plankton that were around. It was quite unusual – we hadn’t seen anything quite like that in the whole 50 years of sampling that we’ve done.
Yosty: What impacts could this have on the rest of the Gulf?
Sonia: It’s still a question we’re working on. Plankton support everything in the ocean. All of the fish and mammals either feed on plankton themselves, or they feed on something that’s been eating plankton already. If there’s not so many of one type of plankton that might be bad, but there were quite a lot of animal plankton around so there obviously eating something. They may be eating something that we don’t see…
One of the things we saw was that the types of plant plankton were slightly different: there were more of the smaller type of cell that are longer and thinner. Those cells typically do better in years when there’s not so many nutrients around, because they find it’s easier to take the nutrients up. It’s possible that those are not such a good food source for some of the animal plankton, or maybe the animal plankton weren’t finding as much of what they wanted and in turn that could mean that there’s not enough animal plankton for the fish and seabirds and mammals. But we still don’t really know – those kinds of patterns take a long time to be revealed.
Yosty: Kathy mentioned something called domoic acid and its potential to impact seabirds. How is this related to the plankton that you’ve been studying?
Sonia: Some phytoplankton – that’s the plant plankton – can produce a toxin called domoic acid. They don’t necessarily produce it over time, sometimes they produce it as a response to a stress in their environment. One of those stresses could be being eaten, so they produce it to put off zooplankton from eating them. There were reported instances of domoic acid in Alaska, and actually through a wide area of the North Pacific a lot of places were reporting it.
Although the plankton have evolved to deal with the domoic acid that’s produced by the phytoplankton when other animals eat the zooplankton they concentrate the toxin, and as you go up the food chain the poison gets concentrated and it can potentially cause problems in larger animals that never ate plankton themselves but have eaten other organisms that have concentrated it. So it’s one explanation for why some of the seabirds may have been struggling in that year.
Plankton are considered one of the environmental drivers, so they’re the link between what happens in the ocean – in terms of water chemistry, temperature, the water conditions – and the fish, because plankton respond to their environment really quickly, and fish feed on plankton and larger organisms feed on fish, so the plankton are the link between the oceanography and the fish.
We know that plankton respond really quickly because they have life cycles that are really short, sometimes even days, but all of them less than a year or at least a year is the longest life cycle. So if changes happen in their environment they respond quite quickly, and you can see that in changes in their numbers, and the types of plankton and where they’re at. So by monitoring them it gives you a really rapid response to a change in the environment.
In the early part of the twentieth century in the UK, it was kind of hard to know where to send the fishing boats, you know, where they were going to find the herring, and Alister Hardy invented this instrument that could be towed behind ships, measuring the plankton, and it’s called the continuous plankton recorder. Continuous because, rather than taking a sample as a snapshot across, it continuously samples the plankton as it goes.
His idea was that if you could understand the food of the herring, the food of the fish, maybe you could predict where they were going to be and then send the fishing boats there. You would build a map, a bit like a weather map, of where plankton were and when they were, and then you could send the fishers. So that was his idea, back in the early part of the early part of the twentieth century. And it took a few years to get routine, but from the 1930s onwards they were using this instrument to do that – to build up a picture of plankton meteorology, basically.
Who is watching the Blob?
Abnormally (adv): different from what is normal
Diverse (adj): a lot of variety
Invertebrate (n): an organism lacking a backbone
Organism (n): an individual life form
Phytoplankton (n): freely floating, often minute plants that drift with water currents
Productive (adj): producing enough energy to sustain life
Zooplankton (n): freely floating animals that drift with water currents
