Aquatic Macro Invertebrate
Investigation of the Shaktoolik River
The Shaktoolik River
The Shaktoolik River is located at 64.333N latitude, 161.153W longitude and is
considered a fifth order tundra river that extends for 90 miles. The mouth of the
Shaktoolik River is at an elevation of 23 feet, with its headwaters nestled in the base of
the Nulato Hills (elevation 400ft). This means from the base of he Nulato Hills to the
mouth of the Shaktoolik River, the river would have an estimated drop of .011 ft/mile
throughout its length. The discharge is approximately 2,000 cubic feet per second.
A tundra river has a surrounding surface soil that tends to be frozen and rocky, however it
thaws in the summer to various depths. The frozen ground and flat terrain on the tundra
slows down the drainage of water. The water that is held at the surface, or upper soil
layer, forms ponds and bogs that provides moisture for plants. This makes up for poor
precipitation levels. The meandering tundra stream has alternating pools and riffles with
low nutrients. Some primary producers that can survive here are Epilithon plus
bryophytes that have moderate productivity. The invertebrate communities have a
moderate diversity with an abundance of insects (Green 1997). Many tundra streams
drain water from the foothills and coastal plains that are underlain by permafrost. The
water in tundra streams is usually clear but can be stained with a light brown color. Many
nutrients are trapped within the permafrost, but will show high pulses of nutrients during
the spring runoff. Low gradient, and stable flows allow for colonization of benthic algae
and insects. Populations of Arctic Grayling are relatively high in tundra streams, which is
due to the stable flow of nutrients and high abundance of macro invertebrates (Green
1997).
Aquatic Macro Invertebrates (AMI) Within Food Webs
Aquatic macro invertebrates (AMI) are important to the food chain, especially for fish.
They feed on bacteria and algae, which are at the lower part of the food chain. Because of
their abundance and position as “middleman” in the aquatic food chain, A.M.I. plays a
critical role in the balance and natural flow of energy and nutrients. As they die, they start
to decay, leaving nutrients behind that are reused by aquatic plants and other animals in
the food chain. The swarm of insects travels downstream and become important food
source to trout, juvenile salmon. Birds, other invertebrates and amphibians.
There is so much diversity in eating habits within the orders of immature insects, like
mayflies, caddisflies, and stoneflies that make it more sense to lump them into guilds. For
example, one particular group of insects is called Scrapers. All of these insects have
mouthparts that allow them to scrape algae and diatoms off of rocks and wood. Big stoneflies, which would be called a Shredder, may get the particles and shreds it into smaller
particles, gets what it wants sending even smaller particles downstream to a waiting a
mayfly who collects it and sends even tinier fragments downstream. All the tiny
fragments maybe filtered out of the water by a true fly larva. These actions of A.M.I.
continue to increase the productivity of river ecosystems.
Biodiversity of Aquatic Invertebrates
Aquatic Biodiversity is when there are many different forms of living organisms in the
stream. Aquatic Macro Invertebrates (“AMI”) can act as a bio indictors of a healthy or
unhealthy river ecosystem. They all have different body shapes and ways of making a
living. By biomonitoring (using living organisms to test the water quality) we can see if
the water quality is either poor or healthy by showing us if there are harmful toxic
substances dissolved in the water. AMI help maintain the health of the water ecosystem
by eating bacteria and dead decaying plants. AMI need high dissolved oxygen levels and
if populations are high, then the river’s oxygen content is good. Here are some things that
can boost oxygen levels: cold water, fast moving currents and little erosional runoff.
Some things that can decrease the oxygen in the water are erosion, pollution and warm
water. If there are a lot of niches in the river then there are a lot of homes, for diverse
organisms. Pollution kills AMI and if there are a lot of AMI then there isn’t any pollution
and the river is healthy. When the water is polluted the AMI are sensitive to these
changes and the aquatic life is affected. Because AMI are so sensitive to changes in the
environment, they can tell us a lot about the health of the ecosystem in which they live
(Jake Doth, 2007).
Order Plecoptera
Over 400 species of Stoneflies belong to the Order Plecoptera. They live in mountain
streams, headwater streams, fast-moving waters, deep rivers, lakes, ponds, and marshes.
Like all insects, they have six jointed legs, a thorax, an exoskeleton, and two pairs of
wings. Immature stoneflies have bodies that are flattened, legs widely spread, tracheal
gills, and are multi-segmented. Adult stoneflies have front wings, long and narrow hind
wings that are shorter than their front wings. (Meyer 2005) Immature stoneflies are
aquatic nymphs. They usually live underneath stones in moving water. The stages of life,
first is the egg, then they hatch into nymphs, and then they grow into adults. Their niche
is in banks of streams, beneath stones, in well-aerated water, and interstitial space
between rocks, where they feed on other insects. Well-aerated water is water with oxygen
in it. In order for stoneflies to have a lot of oxygen, they live in swift moving waters. The
reason why they live in fast moving waters is because the moving water has more oxygen
in it compared to standing water. Rocks cause moving water to swirl even more allowing
more oxygen to dissolve. Stoneflies live in cold swift waters that feed on caddisflies,
mayflies, and true flies. A stonefly may eat detritus (decaying organic matter on the
benthos of the river) or plants when hungry.
Order Tricoptera
The order Trichoptera, also known as Caddis flies are Aquatic Macro Invertebrates with
caterpillar like bodies. Larva have a head with developed mouthparts, thorax and an
abdomen. Their abdomen is usually enclosed with stones, twigs and other natural
materials. Thread-like gills are also attached to it. Adults have filiform antennae, reduced
mouthparts, and long hairy wings held over the abdomen. Caddis flies go through
complete metamorphosis. They lay their eggs by flying close and touching water. Many
species of larvae enter a stage on inactivity called the pupae stage for weeks after they
mature. Their emergence is set off by the cooling of water temperatures in the fall.
Caddis flies pupate in a cocoon spun from silk. They build their cases and attach them to
an underwater object. They close off the front and back of the case to avoid predation, but
still allow water to flow inside it. Once fully developed, Caddis flies use their lower jaw
to cut through their cases and swim up to the rivers surface. They get rid of their skin,
gills and mandibles to come out as fully formed adults. Some Caddis flies swim to shore
and crawl out to emerge. Some species are able to fly right after breaking from their
pupal skin. The adult stage for Caddis flies doesn’t last very long, anywhere from one to
two weeks, sometimes two months. Most adults are non-feeding and simply mate, lay
eggs and die. Caddis flies can be found in rivers or fast flowing streams where there is
more oxygen. Their niche within the ecosystem would be flowing water with a rocky and
sandy benthos. They eat the detritus off the substrate, such as algae and plants. Some
species build silky nets to catch their prey, while others filter food from the river.
Order Ephemeroptera
The order Emphemeroptera, also known as the May flies live in cold or warm water
underneath the rocks. Some mayflies including the hexagenia species can live in mud.
The mayfly life cycle goes through incomplete metamorphosis(no pupae stage). The first
stage begins in the water starting with the egg, which lasts up to a month. The next stage
is the nymph, which can last from 3-4 weeks to 2.5 years. Nymphs are aquatic, have long
antennae, functioning mouthparts, three thorax sections (prothorax, mesothorax,
metathorax) seven pairs of gills and three long tails. The niche they live in are flowing
streams which can help them filter feed without leaving their homes. They eat algae,
detritus (decaying organic matter) and diatomic alga from the substrate of the river
underneath the rocks. The last stage, which is the adult mayflies, can live from 30
minutes to a day. Their mouthparts are reduced, they go through two winged stages called
the subimigo and imago. Some mayflies emerge from nymphs, reproduce and die in a
single day. The major part they play in the food web is feeding the fish in both cold water
streams and warm water streams.
Order Diptera
Tipulids and Chironomids are members of the order Diptera with in the class Insecta.
Diptera are True Flies, which includes chironomids (midges), Tipulids (crane flies), and
hemiptera (water boatman). They live throughout the U.S in streams, ponds, and
ephemeral (temporary) waters, but are most common in streams with flow. Like all
insects, dipterans have 3 pairs of legs, a hard exoskeleton, with a segmented body, and
share one pair of wings. Adults are not aquatic; tipulids when at adult stage literally look
like giant mosquitos with long legs and bodies. Adult midges look like tiny flies with two
pairs of wings. These aquatic macro invertebrates go through metamorphosis, which is
completed through four stages. From first to last, egg, larvae, pupae, and adult. These
insects are only aquatic through the first three, but when they reach adult stage they never
go back to live in the water, only to lay eggs. Their Niche is in water that has current
flowing through the interstitial space or crevasses beneath the rocks on the substrate of
the river. They need flow for support of oxygen that will be pushed around by the current
to the substrate of the river. The critters feed on detritus, which is known as decaying
organic matter on the bottom of the substrate or benthos. All these bugs play a huge role
in the food webs, because they all are prey to the environment that surrounds them. Fish,
other insects, minnow’s, countless birds, shrews and other living mammals eat these
bugs. These bugs are extremely important, because when other living things are growing
up and turning into adults, they need these bugs to eat so that they can grow to become
successful adults. Without insects, all living things that survive on insects would go
extinct, and then this would cause a chain reaction for all living things to go extinct.
Sampling Methods
Our team traveled by jet boat up the Shaktoolik River, 10 miles upstream from the mouth
of the Bering Sea. We stopped at three main river riffle areas with adjacent backwaters
and collected samples of the aquatic invertebrates.
The kick screen was used for collecting large, quantitative samples. One team member
would stand upstream from another holding the kick screen onto the substrate. The
upstream person would disturb one square meter of the substrate by twisting their feet
back and forth amongst the rocks. This would then send the aquatic invertebrates floating
downstream into the screen. After these samples were collected, we would count the
number of aquatic invertebrates on the kick screen. Sometimes, when the amount of
samples was too much, we could divide it into quadrants. We would then count one
quadrant and times it by four to find a rough estimate of the total amount.
While some team members were sampling, others were measuring water depth, water
temperature, the currents speed as well as preparing the aquatic invertebrates in 70%
ethanol solution.
The D-net was used for collecting qualitative samples in the backwaters of the main river.
It is most effective in backwaters when there is no current because the water is still. We
dug the d-net into logjams and undercut banks to see what different types of invertebrates
were living there.
Data Collection
For this investigation our team chose six areas to sample on the Shaktoolik River. Three
main river samples took place on gravel bars and riffle areas. The next three were
sampled in backwater channels adjacent to each main river location. One sample was
taken in a beaver pond, the next in a non-ephemeral channel and the third in a high water
channel that dries up when the water is at a normal level. Two samples were taken from
each location. An abnormal amount of rain created a high water situation during the time
our samples were taken.
Main River Location #1
Large gravel bar on inside bend of the main river.
Sample A.
Medium current speed
Water Depth: 44 cm
Substrate: small gravel < 10 cm
Sample Size: 1M2
Total Inverts: 240
Sample B.
Fast current speed
Water Depth: 60 cm
Substrate: small gravel < 10 cm
Sample Size: 1M2
Total Inverts: 60
Back Channel Location #1
A flooded, ephemeral back channel that had water in it only because of the abnormally
high water in the main river.
Sample A.
Fast current speed
Water Depth: 40cm
Substrate: Small gravel < 6 cm
Sample Size: 1 M2
Total Inverts: 0
Sample B.
Slow current speed
Water Depth: 14 cm
Substrate: Flooded grass
Sample Size: 1 M2
Total Inverts: 4
Main River Location #2
Upstream section of a large riffle.
Sample A.
Fast current speed
Water Depth: < 10 cm
Substrate: Small gravel < 10 cm
Sample Size: 1 M2
Total Inverts: 10
Sample B.
Fast current speed
Water Depth: > 10 cm
Substrate: Medium gravel
Sample Size: 1 M2
Total Inverts: 150
Back Channel Location #2
Adjacent beaver pond and drainage channel. Exploratory samples.
Sample A.
No current speed
Water Depth: 10 cm – 40 cm
Substrate: Littoral bank and wood piles
Sample Size: 1 M2
Total Inverts: 0
Sample B.
Slow current speed
Water Depth: 10 cm – 20 cm
Substrate: Small gravel
Sample Size: 1 M2
Total Inverts: 12
Main River Location #3
Large gravel bar.
Sample A.
Medium current speed
Water Depth: 20 cm
Substrate: Small gravel < 10 cm
Sample Size: 1 M2
Total Inverts: 0
Sample B.
Medium current speed
Water Depth: 53 cm
Substrate: Small gravel
Sample Size: 1 M2
Total Inverts: 0
Back Channel Location #3
Non-ephemeral side channel.
Sample A.
Medium current speed
Water Depth: 35 cm
Substrate: Small gravel < 10 cm
Sample Size: 1 M2
Total Inverts: 12
Sample B.
Medium current speed
Water Depth: 50 cm
Substrate: Small gravel
Sample Size: 1 M2
Total Inverts: 50