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Bob Sterner Chat Session
Moderator: Hello, and welcome to the latest Bell LIVE! chat
session. This afternoon we are going to chat with Dr. Robert Sterner from
the Department of Evolution, Ecology and Behavior at the University of
Minnesota. Why don't we start off by asking Bob what the study of Liminology
is. Testing
Bob Sterner: Hi everyone. "Limnology" may sound like the study
of arms and legs (that's a pun), but instead it is the study of inland
waters, including streams, lakes and ponds.
Moderator: Here is a question from Andrew in Minnesota. "Why are
there so many lakes in Minnesota?"
Bob Sterner: Great question, Andrew! Minnesota has a lot of lakes
because of Geology. About 10,000 years ago, most of the State was covered
by glaciers. When they receeded, they left huge chunks of ice buried in
rock, soil, and gravel. When the ice melted, it left a "puddle" of water
in a depression in the ground. Almost all of our thousands of lakes have
an origin like that. They are called "kettle" lakes.
Moderator: Katie, also from Minnesota wants to know, "What is zooplankton
and what kinds of things to they eat?"
Bob Sterner: That's my research, Katie! I'm so glad you asked.
Zooplankton are small animals from microscopic up to several mm long.
Some are herbivores, meaning they eat "plant" matter, which in lakes is
actually algae. Others are true predators, swimming around seeking out
smaller prey items to grab and eat. Others are "omnivores" meaning they
eat both plant and animal matter, like me.
Moderator: Tony, also from Minnesota was wondering, "What kinds
of things do you do at work?"
Bob Sterner: Um, I didn't mean that zooplankton eat me. I meant
I'm an omnivore.
Bob Sterner: One famous scientist from the University of Chicago
once said that being a scientist is a job where you are glad when it's
Monday. There are so many interesting things I get to do. I spend a lot
of time planning research and working with my undergraduate and graduate
students, helping them do their studies. In the lab, I work with cultures,
microscopes, and the like. On some days, I'm on a boat, getting my samples.
Moderator: Andrew wants to know, "What kinds of microscopes do
you use?"
Bob Sterner: Andrew, I use both "dissecting" and "compound" microscopes.
Very rarely, I use an electron microscope. Electron microscopes are much
more powerful, but more difficult to use so they aren't good for most
of my day to day needs. It takes too long to get images. During the Bell
LIVE! broadcast, I'll have some of my equipment set up and you'll be able
to see the images of plankton were are getting. The microscopes have TV
cameras on them. That's nice for allowing lots of people to see what's
on the 'scope at once.
Moderator: David from Michigan was wondering, "Are there any animals
that like to eat the zooplankton?"
Bob Sterner: You bet there are, David. If you ever caught a bluegill
sunfish with a fishing line, you had a very good "zooplanktivore" or an
animal that likes to eat zooplankton. Many small minnows eat a lot of
zooplankton. Maybe the most famous plankton eater is the sperm whale,
that strains zooplankton like krill out of the ocean water. These big
creatures all depend upon food items that, in lakes and the oceans, come
from tiny plants and tiny animals. Great question.
Moderator: Katie was curious, "What is that green slimy stuff that
floats on the top of lakes?"
Bob Sterner: That stuff is algae, probably what we call "bluegreen
algae". These kind form these surface blooms because they have little
gas vesicles, things that are like baloons. They get bouyancy from those
vesicles, which allows the algae to get up in the light. The vesicles
make the algae move up and down in the water like a submarine, using the
same physical principles to do so. That green slime is ugly and sometimes
toxic to animals. When lakes get this way, the water quality is very bad,
and it is time to do something about it.
Moderator: David from Michigan wants to know, "Do the zooplankton
live in every lake?"
Bob Sterner: Every lake has zooplankton, David. Some more than others,
of course. Understanding those differences is an ecological questions.
Ecologists are very interested in what accounts for the patterns of distribution
and abundance of living organisms. Thanks for the great questions, everyone.
Moderator: Andrew was wondering, "Why do some lakes look like the
water is rusty?"
Bob Sterner: There are several reasons why the water may look rusty.
Sometimes, there actually may be a large source of iron (rust itself).
More likely, the water has a reddish or brownish stain either from organic
compounds that filter out of the soil (just like what happens when someone
makes tea out of dried leaves). There is one type of algae called Oscillatoria
rubescences that makes a very beautiful brownish color. Unfortunately,
that algae also is a signal about poor a water quality. Even some bacteria
can look pretty rusty.
Moderator: Maria from California wants to know, "What do you do
when the water has too much algae in it?"
Bob Sterner: Hello, Maria. Thanks for the question. The first thing
that could be done is to reduce the "point sources" of nutrients. These
are things like pipes from industry or other places that discharge fertilizer
nutrients. Lakes respond to fertilizer just like a lawn. They get a lot
greener. Sometimes, unfortunately, the source of nutrients may be diffuse
and hard to stop. Some scientists have successfully used fish to make
a lake less green. When a lake has lots of big fish, they eat the small
fish, this lets the zooplankton grow, and the algae get eaten. This sounds
pretty complicated, I know, but it's amazing that sometimes it works very
well. Not always, but sometimes.
Moderator: David was wondering, "Could you get sick if you took
a huge gulp of water with zooplankton in it?"
Bob Sterner: An interesting question. I don't know of any zooplankton
that are harmful to people. Some microorganisms can make you sick, and
some people would call these zooplankton too. Most of the zooplankton
I work on are related to shrimp and crayfish. They obviously wouldn't
hurt you if you ingested them. You should bear in mind, though, that lake
water is often not healthy to drink unless it's treated. There are substances
and other kinds of pathogens (germs) that can hurt you or make you sick.
Moderator: Cathrine from Pennsylvania wants to know, "What is your
favorite animal?"
Bob Sterner: I know it's pretty nerdy, but my favorite animal is
the one I work on the most in my research. It's called a "water flea",
or using scientific naming, a "Daphnia". They are endlessly fascinating
to me. Actually, though, I love all animals. I got started in Biology
by watching birds and learning their names.
Moderator: Mr. Nelson wants to know if there is a difference between
the terms "plankton" and "zooplankton"?
Bob Sterner: "Plankton" comes for a Greek word for "wanderer".
It can be used to refer to animals or plants. "Phytoplankton" are the
plants and "zooplankton" are, you guessed it, the animals. There are lots
of other kinds of words used for plankton. For example, plankton that
are *extremely* small (bacteria sized) are called "picoplankton".
Moderator: Katie was wondering, "Did you grow up in Minnesota?
Is that why you like lakes so much?"
Bob Sterner: I was born in a suburb of Chicago. I've lived in Minnesota
a total of about ten years. I'm not sure why I like lakes so much, I just
do. I feel so lucky that I am able to have a job that I love so much.
Moderator: Tony was wondering how you collect the zooplankton.
Bob Sterner: Tony, you'll get a chance to see that on the broadcast
next week. The main trick is to have a net that allows the water to pass
through but catches the zooplankton. The net we use on Lake Superior is
huge, and we use a winch to get it up and down in the water. On small
lakes, we have smaller nets that are easy to use by hand, even sitting
in a canoe.
Moderator: Andrew wants to know, "When you are looking at things
under the microscope how do you keep them from moving around?"
Bob Sterner: One way is to have them on a screen and let the water
drain out. Then, they wiggle a little but can't move too far. Zooplankton
range so much in size and swimming abilty that we use different tricks
for different kinds.
Bob Sterner: Does anybody out there know what the biggest lake
on Earth is?
Moderator: Isn't Lake Superior one of the biggest lakes? Is there
a bigger one??
Bob Sterner: Yup, Lake Superior is the biggest freshwater lake
by area.
Moderator: Okay, one more question from Cathrine, "If you grabbed
a spiney water flea would it hurt your hand?"
Bob Sterner: Great question. Actually, no they don't hurt. However,
the spines do keep some of the smaller fish from eating them.
Moderator: Great chat session everybody! I would like to thank
everyone who participated, and I would really like to thank our host researcher,
Bob Sterner for answering all of our questions. Make sure you look out
for him during the live broadcast on October 12! Next chat session will
be held tomorrow from 12:00 noon until 1:00. See you there!
Bob Sterner: Thanks, everyone.
Bob Sterner: logs off
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Last modified on May 23, 2002.