Q&A: Debbie Steinberg explains zooplankton research in a changing Antarctic

A team from the Virginia Institute of Marine Science (VIMS) is traveling the Antarctic for a six-week study looking at the connection between climate change and variations in the zooplankton population.

As a base component of the Antarctic food web, changes in zooplankton levels or composition ripple up the food chain to affect penguins, whales and other marine life. They also help to move carbon dioxide from the atmosphere into the deep sea, where it contributes nothing to global warming.

Debbie Steinberg, VIMS professor of marine science, first visited the antarctic more than 25 years ago as an undergraduate student. She now leads the research voyage, which is taken annually by a team from VIMS.

The Environmental Monitor caught up with Debbie during her time aboard the research vessel Laurence M. Gould.

Environmental Monitor: What is it like to do research in the Antarctic?

Debbie Steinberg: It’s an adventure, in more ways than one.  First, coming down here is almost like visiting another planet, the environment is so different than what we’re used to.  It is strikingly beautiful – the icebergs, the light reflecting off the water and the ice, passing ice floes with seals and penguins on them.  I have not become jaded yet, I still appreciate the beauty as much as I did the first time I came down here.

EM: Why is it important to study zooplankton populations

DS: Zooplankton (the small animal “drifters” of the ocean) occupy a central position in ocean food webs, as they transfer energy produced from phytoplankton (microscopic plants) through photosynthesis to fish (and other animals higher in the food chain) exploitable by humans.  They also play a key role in nutrient cycling, and in exporting (via sinking of their feces) organic particles to the sea bottom, which provides food for bottom-living organisms and contributes to burial of organic material.

EM: How are the sampling stations set up and how are they constructed?

DS: We sample a 200 x 700 km grid of stations west of the Antarctic Peninsula.  The stations are set up so that we have samples ranging along a gradient from north to south, and from the coast (shallow) to the continental shelf to the continental shelf break (deep water).  It takes us a few hours for the ship to get from one station to the next.

EM: Once you collect the zooplankton samples, what do you do with them?

DS: We catch the zooplankton using net tows. When the tow is brought on board we pour the sample into a large tub so we can see what we caught.  Then we sort the sample on board ship  into the different major categories of zooplankton.  This part is mostly done in our on-board laboratory.  The zooplankton in the Antarctic are quite large, so we can do a lot of this by naked eye, but some species we use the microscopes to sort, which we also have set up on board.    We count the different species, and using the information from a flow meter attached to the net that tells us how much water went through the net, we can calculate density of zooplankton per volume of water.

A 2-meter net used to trawl for zooplankton is lowered off the research vessel Laurence M. Gould. (Credit: Peter Rejcek/National Science Foundation)

EM: What sort of monitoring equipment do you use?

DS: Mostly we use nets, but to catch smaller ‘microzooplankton’ (single-celled animals called protozoans) we use opening and closing water bottles that are mounted on a circular frame with sensors that monitor water temperature and salt content (salinity).  This is called a CTD Rosette – which measures conductivity, temperature and depth.

EM: Is there a time that is ideal for gathering zooplankton?

DS: We can catch zooplankton any time of day or night, and in any season, but in most environments we catch more in the spring than other seasons, and more at night than day.  That is because in the spring/summer is when the phytoplankton bloom (analogous to flowers blooming in the spring on land as temperatures rise and light increases after winter), and the zooplankton increase in numbers because there is more food for them.   Zooplankton tend to be more abundant in surface waters at night because of the phenomenon of “diel vertical migration.” Across the world’s oceans, many zooplankton that live in deeper waters (below the surface sunlit zone) migrate into the surface waters at night to feed. Then, before the sun comes back up, they descend again to reside at their daytime depths.  They do this to avoid getting eaten; their predators can’t see them at night so they can feed under the cover of darkness.

EM: How has the Antarctic changed due to climate change since you began traveling there for research?

DS: I first came to Antarctica when I was in college (in 1987).  When I visited Palmer Station, the U.S. National Science Foundation research station on the west Antarctic Peninsula. During that time I remember hiking up the glacier behind station, which came right up to the doorstep of the station.  I went for a hike up the same glacier last week (26 years later) at Palmer Station, and we had to walk about 200 yards over exposed rocks just to get to the glacier edge. This glacier retreat is real tangible evidence of climate change for me. The west Antarctic Peninsula is one of the fastest warming regions on our planet, and the sea ice is also disappearing, particularly in the northern part of our study area.  This has consequences for the many animals here that depend on the ice, from the krill to the penguins.

EM: The penguin population has gone down in the Antarctic – do you know if there have been drops in the numbers of other species?

DS: We have some evidence that krill may be decreasing in the northern part of our study area, and, in turn, there appears to be an increase in the number, and broadening of the geographic range of another kind of zooplankton – gelatinous salps. Salps are mostly made of water, and not as nutritious as krill for higher predators such as penguins, seals, and whales. So if this is a trend that persists it could lead to decreases in numbers of other animals as well. We are also seeing an increase over the last two decades in other species, such as a species of pelagic (open water) snail called a ‘pteropod’, and in some crustacea other than krill, like amphipods.

EM: How will you use the data collected and what are plans for future research in the Antarctic?

DS: We hope to use the data from our time series to make predictions about future effects of warming on zooplankton communities, and to compare to other sites around the world.  I  hope that others will find the data useful for management, such as for the krill fishery. Our future plans are to investigate some of the possible mechanisms for the apparent change in some of the different zooplankton groups. For example, have there been changes in phytoplankton communities that  are affecting the zooplankton? Are some species of zooplankton under physiological stress due to the warming climate? We have lots of work still to do.

Top image: Kim Bernard and Kate Ruck, members of Dr. Deborah Steinberg’s team, take zooplankton, krill and salps from a bucket to the laboratory on board the research vessel Laurence M. Gould. (Credit:  Peter Rejcek/National Science Foundation)