Macroinvertebrates
An introduction and study
by Puget Creek
Restoration Society
Compiled by Scott Hansen (PCRS), Samantha Dillon (PLU),
Adrian Etlinger (Gilbert High School)
and the Macroinvertebrate
Sampling Crews (2004-06)
Introduction
In the past, people have inflicted damage upon nature for their
own selfish desires without considering the repercussions. Only
recently have people began to rethink their old habits and alter
their lifestyles to better suit the needs of the environment.
The health of rivers and streams are not only important to the
environment, but to human health as well. Fertilizers, acid rain
caused by carbon dioxide emissions, improperly treated sewage,
and toxic chemicals have entered important water systems and
have contaminated this valuable resource. This has lead to
decreases in the wildlife such as salmon that depend on clean
water, and has also polluted drinking water. For ecological as
well as health reasons, it is essential that scientists have a
way to measure the health of streams so that people can prevent
water from becoming contaminated. One measurement involves
macroinvertebtates. Macroinvertebrates are an exceptional
indicator of stream health because they are relatively immobile,
always present throughout the year, easy to collect and
interpret, and are extremely sensitive to pollution.
Abstract
Macroinvertebrate sampling is a widely accepted method used to
determine the health of a watershed. This method is used by many
stream research facilities including Puget Creek Restoration
Society. Macroinvertebrates are important to the ecological
integrity of a stream because they provide food for the fish
that annually return to spawn. Food cycles within the
environment and the river’s condition would suffer without the
constant replenishment of macroinvertebrates. Furthermore,
macroinvertebrates are a useful tool for scientists when
measuring the quality of the water and the health of the
surrounding land. The types and the number of aquatic insects
vary, reflecting a stream’s condition.
What exactly is a macroinvertebrate? Macroinvertebrates are small animals that
do not have backbones and can be seen with the naked eye.
Examples of macroinvertebrates include: aquatic insects,
crustaceans, worms, snails, and clams. “Benthic,” meaning
bottom-dwelling, is a word that is often associated with
macroinvertebrats because they live in and among the debris on
the bottom of the streambed (Stream Bug Monitoring).
There are many variations of
macroinvertebrates. They are all divided into categories, which
define their lifestyle of how they obtain food. Each of these
aquatic insects has a different lifestyle than the other.
Behavior/Lifestyle
Because macroinvertebrates live on various
substrates and conduct themselves in various ways, they are
divided into groups that define their behavior, including:
Burrowers:
live among silt, sand, and organic material.
Clingers:
attach to substrates in current.
Climbers:
move vertically on plants or debris
Sprawlers:
live on top of plant debris or soft substrates.
Swimmers:
cling to submerged objects and swim through the water column in
short bursts.
The behavior of Macroinvertebrates
corresponds to the lifestyle that is best suited for them. For
example, a clinger inhabits the fast flowing part of a stream
within the thin tree cover and scrapes algae off of rock
substrates for food. A clinger has the ability to cling to rocks
and not be carried away by fast flowing water. Another type of
macroinvertebrate-a burrower-spends its time on the bottom of a
stream and is a collector-gatherer because it is where organic
material accumulates. Additionally, a burrower can dig a home
for itself in the ground.
An aquatic insect’s behavior is also
interconnected with its feeding method. Each type of aquatic
insect has a different way of acquiring nourishment:
Shredders:
shred large pieces of organic material such as leaves or twigs.
They inhabit parts of the river that have a dense canopy cover,
where plant matter is likely to fall into the stream for them to
shred.
Scrapers:
eat algae that coat underwater surfaces. Live in portions of the
stream with a thin canopy cover so the sun’s light can reach the
bottom of the stream and stimulate algae growth.
Collector-filterers: filter fine particles of decomposing
organic matter suspended in the water.
Collector-gatherers: gather fine particles of decomposing
organic matter from the substrate or surface film.
Predators:
eat living animals, usually other macroinvertebrates, but are
also known to eat fish and amphibians as well.
Role in the Food Chain
If it weren’t for macroinvertebrates
nutrients wouldn’t be broken down, distributed, and recycled
back into the stream. Some aquatic insects are herbivores,
others are carnivores, and others are detritivores. Predators
then consume the herbivores. When the predators or herbivores
die, their bodies decompose and the detritivores feed on the
matter, completing the cycle.
Macroinvertebrates also play a significant
role in the larger picture of an ecosystem. Most
macroinvertebrates generally eat the fungi and bacteria growing
on plants and rocks, and other aquatic insects. Small fish, such
as trout and salmon, rely on aquatic insects for sustenance.
Also, animals such as herons and orcas prey on the fish. Without
macroinvertebrates this whole cycle would collapse. There would
be nothing for the juvenile fish to eat, thus they would move to
other areas and there would be no food for the herons and orcas.
This process would just continue to affect every animal in the
ecosystem until the watershed that was once rich with wildlife
has been reduced to a desolate landscape where wildlife is
scarce. In the past, this has occurred because of people’s lack
of concern for the environment. Humans have altered many
communities of rivers by eliminating much of the vegetation,
consuming too much water for their personal needs (drinking,
dishwashing, etc), and dumping products such as fertilizers,
improperly treated sewage, and toxic chemicals from factories,
polluting the environment and contaminating people’s drinking
water. This has a negative impact on the habitat of
macroinvertebrates. The characteristics of a stream can quickly
and drastically change. Many of the macroinvertebrates die,
while only a few species survive.
Indicators of environmental health
Aquatic insects are not only important to
the ecosystem of a stream, but are important in helping to
maintain a healthy environment as well. By measuring the
population and different types of macroinvertebrates, scientists
are able to tell whether a stream is healthy or being affected
by other potentially dangerous processes such as eutrophication.
Eutrophication is when a river develops a high level of
dissolved nutrients that stimulate algal growth. Although
macroinvertebrates feed on algae, too much present could be very
overwhelming and harmful to a stream ecosystem due to nutrient
enrichment. Harmful substances being jettisoned into rivers and
streams causes this.
The health of rivers and other water
resources must be restored for both the health of wildlife and
human society. It is essential for scientists to have a way to
monitor the environment to prevent anymore harm being done. The
population and diversity of macroinvertebrates differs due to
the river’s condition. Macroinvertebrates provide a natural
indicator of a river’s health. Many macroinvertebrates perish in
polluted rivers because they can only survive under a very
narrow range of conditions. Few can withstand the changes that
occur. By measuring the population and different types of
macroinvertebrates, scientists are able to tell whether a stream
is healthy or polluted. Therefore, aquatic insects are not only
important to the ecosystem of a stream, but are important in
helping to maintain a healthy and clean environment as well.
Collection Method
By calculating the populations and
different types of aquatic insects, scientists can figure out
whether a river is healthy or if it is polluted. There are
specific species of macroinvertebrates that are particularly
intolerant to pollution. The most sensitive to pollution
include: stoneflies, mayflies, and caddisflies (Karr). If there
are few of these species present, this would indicate that the
stream is polluted.
Within the Tacoma area, Puget Creek
Restoration Society has done macroinvertebrate sampling in both
Puget Creek and Mason Creek since 2004. Benthic
macroinvertebrates are quite easy to collect. When choosing a
spot to sample, it is important to find a riffle, or area of
brisk-moving water, that is long and straight enough to include
three samples about five meters apart from each other; one
mid-stream, one down-stream, and one up-stream. The equipment
used to collect with is relatively inexpensive. Usually, a
Surber sampling net is used. It is a one foot-by-one foot net
that is placed in the center of a stream into the sediment.
Then, a one foot-by-one foot area is disturbed in front of the
net, about ten inches deep into the sediment. Large rocks within
this area a scraped off into the net as well. As the water flows
past, macroinvertebrates are captured in the net. This process
is timed for one minute and is done three times within a riffle.
Macroinvertebrates are then to be separated from the sediment
and placed into separate jars filled with alcohol to preserve
them.
After the samples have been collected and
carefully placed into separate jars, they are analyzed in a lab.
They are identified and counted. Pierce County uses a method
referred to as the Benthic Index of Biological Integrity or
B-IBI to categorize the macroinvertebrates and produce a “report
card” for the macroinvertebrate community as well as the health
of the stream. The B-IBI is made up of ten different aspects
(often called metrics) such as: species diversity, number of
total insects, presence of tolerant or intolerant insects,
feeding ecology, and population structure. A value is assigned
for each aspect. The values are 1, 3, or 5. A score of 5 would
indicate little or no degradation and a score of 1 would
indicate severe degradation. The ten separate numbers are added
to produce a total score ranging from 10 to 50 (Bugs are Good
Indicators).
Results
As stated previously, Puget Creek
Restoration Society has collected macroinvertebrates and had the
results analyzed for 2004, 2005, and 2006. For each site, B-IBI
scores have been given to each separate sample and the three
samples have been averaged to give a total composite B-IBI score
for the creek for a specific year. The data for Puget Creek and
Mason Creek is as follows:
|
|
2004 B-IBI score |
2005 B-IBI score |
2006 B-IBI score |
|
Puget Creek |
16 |
24 |
22 |
|
Mason Creek |
22 |
24 |
22 |
According to the ten-metric B-IBI Scoring
system, a score between 10 and 16 indicates a stream that is in
very poor health. A score between 18 and 26 indicates a stream
that is in poor health. A score between 28 and 36 indicates a
stream this is in fair health. A stream with a score between 38
and 44 indicates that that stream is in good health. And a score
between 46 and 50 indicates that the stream is in excellent
health. As we can see, both Puget Creek and Mason Creek are in
poor health for all three years, and Puget creek was in very
poor health in 2004. A similar pattern has occurred with both
creeks over the course of three years. In 2004, both creeks were
at their lowest numbers. In 2005, both creeks improved slightly.
And in 2006, both creeks decreased in health again. We can
conclude that Puget Creek is slightly less healthy than Mason
Creek. This makes sense when we look at the physical properties
of both creeks. Puget Creek has a walking path right next to it
and lies closer to a residential area, making it more vulnerable
to human alteration. Mason Creek has no public paths next to it
and is much more meandering and close to a natural path of a
creek.
In Conclusion
The stream ecosystem is a complicated
relationship between plants, animals (including humans),
physical and chemical components. Thus the health of the stream
is very important. In order to assess the health, we can look at
many different aspects of the ecosystem, one of them being the
abundance and diversity of macroinvertebrates.
Macroinvertebrates are extremely sensitive to changes in the
environment. Therefore, they make an excellent indicator of
stream health. Locally, Puget Creek and Mason Creek have been
studied using macroinvertebrate data for the past three years.
Although the data from both streams indicates the creeks to be
in poor condition, many efforts have now been made to improve
their conditions, both for the surrounding wildlife and for
human purposes. It is our responsibility to rethink our old
habits, to live in harmony with nature, and to keep the Earth
clean.
Works Cited
“Bugs are Good Indicators for the Health of
a Stream.” King County, Washington.
http://dnr.metrokc.gov/wlr/waterres/bugs/indicator.htm. Accessed
6/20//2006.
Karr, James R. “Biological Integrity: a
long-Neglected Aspect of Water Resource Management.” Virginia
Polytechnic Institute. Ecological Society of America:1991. Pgs
66-84.
“Stream Bug Monitoring.” King County,
Washington.
http://dnr.metrokc.gov/wlr/waterrs/Bugs/. Accessed
6/20/2006.
APPENDIX A
Sampling information
Puget Creek Macro 2004
|
|
%EPT |
%Ephem |
%Pleco |
%Trich |
%Dip |
%Chiro |
%Oligo |
%Filtr |
%Scrap |
lat |
long |
|
1 |
13.33 |
11.11 |
0.00 |
2.22 |
11.11 |
8.89 |
42.22 |
2.22 |
6.67 |
47.28 |
122.48 |
|
2 |
6.47 |
1.44 |
5.04 |
0.00 |
17.99 |
14.39 |
39.57 |
5.04 |
10.79 |
47.28 |
122.48 |
|
3 |
5.13 |
1.28 |
2.56 |
1.28 |
16.67 |
14.10 |
28.21 |
5.13 |
11.54 |
47.80 |
122.48 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Rep. |
%Cllct |
%Pred |
%Shred |
ClngPTax |
%ClngP |
TotTaxa |
EPTTax |
EphemTax |
PlecoTax |
|
|
|
1 |
64.44 |
22.22 |
0.00 |
0.00 |
0.00 |
9.00 |
2.00 |
1.00 |
0.00 |
|
|
|
2 |
56.12 |
23.74 |
2.16 |
1.00 |
5.04 |
14.00 |
3.00 |
2.00 |
1.00 |
|
|
|
3 |
46.15 |
35.90 |
0.00 |
2.00 |
3.85 |
12.00 |
3.00 |
1.00 |
1.00 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Rep. |
TrichTax |
DipTax |
ChiroTax |
IntolTax |
%Toler |
%1Dom |
HBI |
LongLived |
Dom3% |
|
|
|
1 |
1.00 |
2.00 |
1.00 |
0.00 |
53.33 |
42.22 |
7.94 |
1.00 |
76.00 |
|
|
|
2 |
0.00 |
5.00 |
1.00 |
1.00 |
55.40 |
39.57 |
7.96 |
1.00 |
73.00 |
|
|
|
3 |
1.00 |
3.00 |
1.00 |
1.00 |
47.44 |
32.05 |
6.98 |
1.00 |
74.00 |
|
|
Puget Creek Macro Scoring 2004
|
Scoring
Biometrics |
|
|
|
|
|
|
|
|
Site |
Puget
Creek |
Rep. |
A |
Date
Collected |
16 Oct.
2004 |
|
Metric |
|
|
No./% |
|
Score |
|
Total |
|
|
Total
no. of taxa |
|
9 |
|
1 |
|
16 |
|
|
No. of
Ephemeroptera taxa |
1 |
|
1 |
|
|
|
|
No. of
Plecoptera taxa |
0 |
|
1 |
|
|
|
|
No. of
Trichoptera taxa |
1 |
|
1 |
|
|
|
|
No. of
Long-lived taxa |
1 |
|
1 |
|
|
|
|
No. of
Intolerant taxa |
|
0 |
|
1 |
|
|
|
|
% of
individuals in tolerant taxa |
53.33 |
|
1 |
|
|
|
|
% of
predator individuals |
22.22 |
|
5 |
|
|
|
|
Clinger
taxa |
|
0 |
|
1 |
|
|
|
|
%
dominance (3 taxa) |
76 |
|
3 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Scoring
Biometrics |
|
|
|
|
|
|
|
