“How Do You Make A Lake Trout?”
ENVE1501 - Environmental Engineering
An Exploration Aboard the R/V Agassiz
Ms. Anika Kuczynskt & Dr. Marty Auer
The Department of Civil & Environmental Engineering
Michigan Technological University
How Do You Make A Lake Trout?
All living things need chemicals to provide structure and
energy to provide power. Chemicals are available in the
air, water and soil and energy is available from the sun.
However, these sources of chemicals and energy are not
directly available to a lake trout. The chemicals and
energy must be collected and converted to an available
form. This is the job of the food chain.
In this exploration, we will examine the base of the food chain
where chemicals and energy are first captured and higher levels
where they are transferred to make a lake trout!
Today on the Boat
We will collect plankton samples from the water using a fine
mesh net and sediment samples from the lake bottom using a
PONAR dredge. The sediment samples will be processed with a
sediment elutriator (critter catcher) to separate out the
animals.
Food Web
The exploration is based on the concept of the
food chain. In nature, material and energy
transfer are a bit more complicated, involving a
collection of food chains or a food web
Lake Trout
Whitefish
Herring
Zooplankton
Sculpin
Benthic Invertebrates
settling
Phytoplankton
No,
fool.
A food
web!
Phytoplankton
Phyto = plant
Green algae
The capture of chemicals and energy
in lakes is the job of plants, including
larger species such as water lilies
and smaller forms called algae.
Image by Spike Walker
Plants take chemicals such as carbon , nitrogen and phosphorus
directly from the water and use built in ‘antennae’ (chlorophyll)
to capture the sun’s energy. The chemicals and energy are
then combined through the process of photosynthesis to make
more plant material.
CO2 + H2O  C(H 2O) + O2
The phytoplankton (free-floating algae) capture chemicals and
energy, but a problem remains in making a lake trout . The
phytoplankton are microscopic and thus are too small to make
a suitable meal for a large fish. It is the job of the higher levels
of the food chain to concentrate the chemicals and energy,
ultimately making them available to the lake trout.
cyanobacteria
diatoms
Plankton =
freefloating
http://user.unif-rankfurt.de/~schauder
/cyanos/cyanos.html
http://wfrc.usgs.gov/research/fish%2
0populations/STMaule5.htm
Paradox of the Plankton
Paradox =
mystery
The Competitive Exclusion Principle states that whenever two
species compete for the same resource, one species will win,
eliminating or excluding the other species.
Yet, when we look in lakes and oceans we see a tremendous
diversity of species. Does this violate the principle?
http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial30.htm
Know any
algae tricks?
As you look through the microscope
Today, consider what ‘tricks’ different
algae might use to gain an edge over
its competition.
Zooplankton
Zoo = animal
Zooplankton are microscopic, free-floating animals that
graze on the phytoplankton, concentrating the chemicals
and energy captured lower on the food chain and
transferring it to higher levels.
There are three major types of zooplankton, listed here
in increasing order of size: rotifers, copepods and
cladocerans.
cladoceran
rotifer
copepod
Image by
Ron Neumeyer
http://www.hudsonregional.org
/mosquito/program.htm
Image by
Spike Walker
Most zooplankton are filter-feeders, using beating hairs
or ‘arms’ to create currents that funnel the
phytoplankton and other particles into their ‘mouths’.
Plankton =
free-floating
Negative Phototaxis
Photo = light
Zooplankton exhibit a behavior called negative phototaxis,
meaning that they ‘fear’ light. Because of this behavior,
most zooplankton are found well below the surface in the
daytime, migrating toward the surface to feed on
phytoplankton at night.
Computer image of a
layer of zooplankton
located 25-45 meters
below the surface in
Lake Superior.
Can you imagine how
zooplankton might benefit
from this behavior?
Taxis = touch
Benthos
The benthos are animals that make their
homes on and in the bottom sediments of
lakes. Forms familiar to many of us include
snails, clams, and zebra mussels. A shrimp-like
organism, Diporeia, is the primary food source
for lake whitefish. The early life stages of
insects are among the most common
members of the benthos and are of great
importance in the food chain.
Benthos
= bottom
zebra mussels
http://users.mo-net.com/
flotilla6/zbra_msl.htm
McKenna 2007
http://epa.gov/greatlakes/
active/2004/jul04.html
The benthos might be considered a lake’s clean-up crew.
Phytoplankton that settle to the lake bottom, especially
species that are to large to be consumed by grazing
zooplankton, are collected by the benthos. Bottom-feeding
fish then prey upon the benthos, transferring the chemicals
and energy up the food chain.
Benthos – familiar faces: bloodworms
The bloodworm is one of the most common
members of the benthos in Portage Lake. They
are not ‘worms’, but rather the larvae stage of
the midge, a non-biting insect related to the nosee-um.
Adult midges lay their eggs (up to 3,000 in a single
mass) on the surface of the water where they sink
to the bottom and hatch in about a week. After
hatching, they become larvae (bloodworms),
burrowing into the mud and feeding on settled phytoplankton
and dead organic matter.
After several weeks in the mud, the larvae become
pupae and swim to the surface where they are
emerge as adults. The adults do not feed and only
live about 3-5 days. Adult midges are often seen in
summer as swarms around outdoor lights.
They are called bloodworms
because of their red color, a result
of high levels of haemoglobin in
their blood. As in our bodies,
haemoglobin carries oxygen and
helps the midge larvae inhabit low
oxygen environments in the mud.
My latin
name is
Chironomus
Source: http://ohioline.osu.edu/hyg-fact/2000/2129.html
Benthos – familiar faces: phantom midges
A second common member of the
benthos in Portage Lake is the phantom
midge, a relative of the bloodworm. But
unlike the bloodworm that eats settled
phytoplankton and dead organic matter,
phantom midge larvae a carnivores (meat
eaters) preying on zooplankton.
Many organisms have developed special
http://www.life.uiuc.edu/ib/109/
‘tricks’ to help them better survive in
nature. The high haemoglobin levels in bloodworms is one
example. Can you figure out what the phantom midge’s trick is?
What are two reasons why this might help it survive?
The dark spots in the
otherwise transparent body
of the phantom midge are
swim bladders that help
them float.
My latin
name is
Chaoborus
http://www.microscopyuk.org.uk/mag/indexmag.html?http://www.microscopyuk.org.uk/mag/artmay05/swgallery1.html
Fish - Planktivores
Fish that depend on zooplankton as
their major food source are called
planktivores.
Plankton =
free-floating
plants and
animals
These fish filter or strain
zooplankton from the water using
comb-like structures called gill
rakers. Particles trapped by the gill
rakers become more concentrated
as they move further into the
mouth and the fish finally swallows
a soup of plankton.
rainbow
smelt
http://www.nature.com/nature/journal/v412/n6845/fi
g_tab/412387a0_F1.html
commons.wikimedia.org
lake
herring
http://pond.dnr.cornell.edu/nyfish/Salmonidae/cisco.html
Rainbow smelt and lake herring are common planktivores in Lake
Superior and are major food sources for lake trout
‘vore’ = eat
The annual smelt run attracts fishing
enthusiasts from around the region. Lake
herring are caught commercially, smoked
and sold in fish shops around the lake.
Fish - Benthivores
Benthi =
Bottom animals
Fish that depend on benthos or bottom
animals as their major source of food are
called benthivores. Fish that feed in this
manner have specially-developed mouths
that make it easier to capture their prey.
Sturgeon with mouth extended
www.anglinguk.net
The lake sturgeon is a benthivore common to Lake Superior that
grows to lengths exceeding 6 feet and can weigh more than 100
pounds. Other bottom-feeding fish in Lake Superior include the
whitefish and the sculpin which prey on the crustacean Diporeia.
Lake Whitefish
www.rudybenner.com
‘vore’ = eat
Sculpin
http://www.nanfa.org/NANFAregions/oh/Ohio0802/
Fish - Piscivores
Pisci = fish
Fish that prey on other fish as their major
source of food are called piscivores. The
dominant native piscivore in Lake Superior
is the lake trout.
Fish biologists recognize to
different strains of lake trout in
Lake Superior: leans and
siscowets (or fats). The diets of
the two strains differ because
leans live in shallow water and
fats in deep water. Leans favor
smelt as prey, while the diet of
fats is more varied and includes a
http://dnr.wi.gov/org/caer/ce/news/DNRNews
significant number of sculpin.
Fats
Leans
Stickleb
acks Others
Sculpin
Others
Stickle
backs
Herring
Smelt
Sculpin
Smelt
‘vore’ = eat
Herring