Ultraviolet Radiation Gives Microbes Mixed Messages (Cont.)
Page 2/2 - Posted May 15, 2018
What's Happening at the Ecosystem Level?
Photo Credit: Benjamin Van Mooy
Samples left out in the sun let the research team gauge how much ultraviolet radiation from the sun might affect the microorganisms in the harbor.
The research team is looking for evidence of this happening in the oceans around the Antarctic Peninsula, which experiments have shown can happen in a lab and can cause serious problems in organisms higher in the food chain.
“Now what we’re curious about is what is the effect of this process on the ecosystem scale and is this short circuiting the ability of these organisms to carry out their really important jobs in this ecosystem,” Collins said.
The effects of these ultraviolet-induced infochemicals could be significant and reverberate throughout the food web.
“These molecules when they are produced [in phytoplankton] and the phytoplankton are eaten by copepods or zooplankton, they can give the copepod progeny birth defects,” Van Mooy said. “That would represent a short circuit in the flow of nutrients and energy through the food web. That’s just one example, there are other examples also.”
The waters around the Antarctic Peninsula are where these ultraviolet-induced infochemicals are likely to have the biggest impact. The Bellingshausen Sea teems with life while at the same time being exposed to intense doses ultraviolet radiation.
“We think it’s really important in the Antarctic because of this link to UV radiation, which is so intense in the Antarctic region,” Van Mooy said. “Per photon, there’s more UV here than anywhere else.”
The cause of this excess ultraviolet radiation over the Antarctic region is the seasonal thinning of the Earth’s protective layer of ozone in the stratosphere. The planet’s ozone layer blocks most of the harmful ultraviolet radiation emitted by the sun. However a seasonal hole in that ozone layer, first identified in 1985, means that significantly more radiation penetrates through.
The researchers traveled to Palmer Station early in the austral summer to catch the ozone hole when ultraviolet radiation was at its most powerful. Even though the ozone hole itself is thinnest earlier, in August, the sun is only above the horizon for a short period of times and a limited amount of radiation passes through. As the sun stays out longer and rises higher in the sky, a net amount of more radiation passes through until the hole closes up in November.
“There’s kind of a little window here. October and early November are the times when it peaks,” Van Mooy said. “There’s a cycle in the ozone hole but then there’s increasing sunlight because of the season, so you hit a sweet spot this time of year where the ultraviolet is the highest.”
Though recent evidence shows that the ozone hole is in the process of healing, it’ll still be about 70 years or so before it’s mostly closed up. At the same time, because of climate change many organisms are migrating farther south or starting their lifecycles earlier in the summer, when the hole is at its biggest.
“The ozone hole is centered primarily further south,” Van Mooy said. “What we’re finding is that the climate is changing and the habitats are drifting further and further south. So it stands to reason that things that used to happen in December at a lower latitudes are now happening earlier in the season at a higher latitude, so you can imagine that the UV flux could be very different in those two situations, both because of the geographical shift and the timing shift.”
For the phytoplankton and algae at the bottom of the food chain, this all happens at a particularly critical time in their lives. Early spring and summer, as the ice is breaking up, is when they are at their most productive, to replenish after the long dark winter.
“Almost all of the photosynthesis occurs in this pretty short period of time there, and that just so happens to coincide with when the ozone is at its thinnest,” Collins said.
While at the station the team collected open-water samples from the sides of the station’s boats, as well as from under the ice itself.
“We primarily took water samples,” Van Mooy said. “We would filter them for the microbes and other plankton that were in them, and preserve those samples of the plankton and the microbes and then shipped them back to the lab.”
"Per photon, there's more UV (ultra-violet radiation) here than anywhere else."
Benjamin Van Mooy
Since returning to Woods Hole, they’ve begun analyzing the samples with a mass spectrometer, looking for all the different kinds of lipids.
“With the samples from Antarctica, we’re routinely seeing about a thousand different lipid molecules in the samples that we collected,” Van Mooy said.
They also conducted a few experiments at Palmer Station, looking for the production of these reactive oxygen species. Some of the water samples they collected they placed under snow-covered ice to block the light.
“Since we were interested in light, we wanted to have a really authentic kind of dark control,” Van Mooy said. “We measured the production of these reactive oxygen species... As a comparison to the other things that we did in the sunlit waters, we wanted to have this dark end member to really get a sense of what kind of refuge from the light the ice provides for the microbes that live in the water there.”
Later this year the team will sail on the Research Vessel Laurence M. Gould to collect samples near the edge of the winter sea ice.
“There’s a lot of really interesting chemistry that happens there,” Van Mooy said.
When seawater freezes during the long dark winter, much of the salt leeches out, so the ice ends up being mostly fresh water. At the end of winter, the fresh water melting off of the ice is less dense than the salty seawater and makes a layer of fresher water at the surface of the ocean.
“The fresh water and the salt water don’t mix very well, and that keeps phytoplankton in that fresher water, up in the sunlight,” Van Mooy said. “It focuses them near the surface. There’s been some work showing that in seasons where melting at the ice edge is intense, there’s a really nice lens of fresher water that phytoplankton do better in and where productivity can be higher, but the down side is they’re also focused in the UV light as well, which potentially makes them susceptible.”
After the two field seasons, the team will have a tremendous amount of data and samples to sift through.
“Half of the battle is getting through all the data and making sure we’ve identified all the molecules and quantified them correctly,” Van Mooy said. “We’re still early days in the project for sure.”
NSF-funded research in this story: Benjamin Van Mooy, the Woods Hole Oceanographic Institution, Award No. 1543328.