Hester-Dendy Sampler Collection at the Chagrin River and Dipnetting for Macroinvertebrates at a Lentic Pond in the West Woods (3 October 2013)
Our Chagrin River field site
Today we returned to the Chagrin River, which runs
through the South Chagrin Reservation of the Cleveland Metroparks, to
check on our Hester-Dendy (H-D) samplers from 19 September 2013. It was
noted that in the two weeks since we had been to the site to place our
H-D samplers, the leaves from riparian vegetation had begun to fall into
the river, producing a significant coarse particulate organic matter (CPOM)
input. It was a cloudy, but pleasant day for rounding up
macroinvertebrates, with a temperature of 25°C.
Using the
flags on the trees as our guides, we search the stream for the flagged
bricks anchoring our Hester-Dendy samplers. Good eye, Cameron!
Hester-Dendy samplers consist of wooden block
substrates separated by spacers along an eyebolt and held in
place by a nut. Although researchers utilizing H-D samplers leave them
in the environment for longer periods of time (about eight weeks) to
allow for a more complete representation of species present in the
system, after a brief inspection of our samplers, it was determined that
for our class’s purpose, two weeks was adequate for a “decent”
colonization of species. Typically, grazers and shredders are the first
to colonize the wooden board pieces, with predators moving in afterward.
We predicted that a few species of trichopterans would likely be found
on the samplers.
Ziploc bags
are used to enclose the H-D samplers immediately after they are removed
from the water to ensure that specimens do not get the opportunity to
escape.
We were able to recover the H-D samplers by finding
the orange flags attached to trees along the side of the river and
searching the water perpendicular to their location. The samplers were
attached to bricks so that they would not be carried away by the
current. We were relieved to find that our Boy Scout-approved knots held
up and that all of our H-D samplers were recovered.
When a flagged brick with samplers attached was found, the brick was
removed from the water first and carried toward the location of the
samplers. It was important to have a Ziploc bag ready before taking the
samplers out of the water because organisms tend to drop-off once the
samplers are removed. Each sampler was placed in its own Ziploc bag and
then all the samplers and the attached brick were placed in a garbage
bag.
These biologists are not afraid to get their hands dirty rustling rocks to release macroinvertebrates into the seine net.
After we recovered all the samplers, we used a method
called kicknetting to sample the riffle zones for more
macroinvertebrate species. This method of sampling involves placing a
one meter square seine net along the bottom of the river in a riffle
zone and disturbing the area immediately upstream by flipping over and
rubbing rocks to release attached macroinvertebrates. These
macroinvertebrates then flow with the current and get trapped in the
seine net. Making sure that the bottom of the net is flush with the
sediment and that the net is quickly scooped to the surface after
collection is complete are important measures to prevent the loss of
specimens. We searched the seine net, gently removed macroinvertebrates
with forceps and then placed them in vials containing 70% ethanol.
Our West Woods field site
The
next site that we visited was a lentic pond in the West Woods, which is
part of the Geauga Park District in Novelty, OH. We expected to find
predacious hemipterans and odonates in this non-moving body of water.
A triangle dipnet can be used to collect macroinvertebrates from the pond substrate and littoral macrophytes.
The method we used to collect specimens is called
dipnetting, which is ideal for pond sampling, but may also be used in
streams. The optimal type of net to use for dipnetting is called a D
net, which is shaped like a capital letter D. The flat side of the “D”
is used to bump along bottom of the pond to disturb the sediment and
vegetation at the benthos to collect macroinvertebrates. Since JCU does
not own D nets, we used triangle nets for our collection.
In the photo
on the left, biologist Ben is having the time of his life dipnetting for
macroinvertebrates! In the photo on the right, Cameron carefully sifts
through sediment and vegetation looking for macroinvertebrates in his
dipnet haul.
After bumping the net along the bottom to stir up the sediment, it is
quickly scooped to the surface so that specimens do not have a chance to
escape. In addition to the expected odonates and hemipterans, we caught tadpoles in our nets.
Back
in the laboratory, the proper method of organism collection from the
H-D samplers was demonstrated. First, for convenience, the rope
connecting the samplers to the brick was cut. The nut holding the wood
blocks to the eyebolt was then removed. Next, the wood block substrates
were each systematically searched on both sides for macroinvertebrates,
which were removed gently with forceps and placed in a 70% ethanol
solution. Alcohol also was used to rinse sediment from the substrates to
ensure that no specimens were overlooked.
Note the
caddisfly cases attached to the wooden block. These cases are made from
detritus and allow the caddisflies to withstand the fast-moving current
of the riffle zone.
It was observed that several wooden blocks had the
cases, or retreats, of caddisfly (trichopteran) larvae attached to them. The leaves
that were found attached to the H-D samplers were also searched for
organisms.
Using a dichotomous key to identify a specimen of family Simuliidae
The collected specimens were then examined under the dissecting microscopes. Finer
taxonomic distinctions of organisms from familiar invertebrate orders
were accomplished by the use of dichotomous keys from the Guide to Aquatic Invertebrates of the Upper Midwest.
Dichotomous keys use specific morphological characteristics presented
in a certain sequential order to distinguish taxonomic rankings.
The flathead mayfly of family Heptageniidae
Ephemeropterans (mayflies), trichopterans
(caddisflies) and pelcopterans (stoneflies), which are classified as
"pollution sensitive" taxa are used as bioindicators of water quality in
a measure called an EPT Index. The EPT Index quantifies the health of a
stream by the number of species of these orders present, with healthier
streams containing a larger abundance of these orders. The
ephemeropteran families collected included Baetidae, the small minnow
mayflies, and Heptageniidae, the flathead mayflies. Baetidae are strong
swimmers and can have antennae longer than twice the width of their
head. Members of Heptageniidae, like their common name implies, have
flattened heads, bodies, and legs.
Note the hardened exoskeleton on the head (characteristic of trichopterans) of this member of Philopotamida (center specimen)
A few trichopteran families were also collected,
including Hydropsychidae and Philopotamida. Species belonging to
Hydropsychidae, the common net-spinner caddisflies, can be distinguished
by a conspicuous brush of hairs on the posterior of the abdomen. A
defining characteristic of philopotamidans, the finger-net caddisflies,
is a T-shaped labrum, which is a structure located between the
mouthparts. Philopotamidans are filter feeders that spin nets to trap
edible particles from the water and then use the labrum to scrape the
food from the net. No plecopteran species were found on the H-D
samplers.
Representing Diptera (true flies) was a specimen from
family Simuliidae, the black flies. Black flies have a ring of hooks on
the posterior of the abdomen that allows them to attach to substrate
and withstand the water current. A larval coleopteran (beetles) from
family Elmidae, the riffle beetles, was also collected. As their common
name suggests, riffle beetles are found in fast-moving and highly
oxygenated areas of streams.
Check out this radical anisopteran that we collected from the West Woods!
Finally, a nymph odonate belonging to suborder
Anisoptera was collected from the West Woods. As we learned from
lecture, anisopertans (dragonflies) are distinguished from damselflies
(zygoptera) because in the larval stage their head is the same width or
narrower than their thorax and abdomen, they do not have three elongate
gills extending from the posterior of their abdomen and in adults, their
wings are spread out when resting.
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