SHRIMP LAB TEACHER BACKGROUND & INSTRUCTIONS
Solving a mystery
The blue mud shrimp, Upogebia pugettensis, and the California ghost shrimp, Neotrypaea
californiensis, are the most abundant shrimp in Oregon estuaries. Both species are long lived as
adults and form dense beds on intertidal mudflats in estuaries where they seem to have few
predators. The populations of both shrimp are easy to measure because their dense beds are easy to
find and sample. Both of these shrimp are very important in estuary ecosystems. Alas, all
populations of both species are rapidly declining in Washington and Oregon.
These shrimp produce larvae that go to sea and return as post-larvae which return to
estuaries and settle back into the shrimp beds. Their populations are declining because they don’t
end up with enough post-larvae (babies) to replace the dying adults each year.
The mud shrimp has a new introduced parasite that prevents reproduction of larvae but this
parasite only infests mud shrimp. The ghost shrimp has another parasite that also prevents
reproduction but is too rare to reduce ghost shrimp reproduction significantly and ghost shrimp
produce plenty of larvae each year. Why ghost shrimp populations are shrinking even faster than
mud shrimp populations is a giant mystery.
Only the mud shrimp has an obvious parasite problem and loss of reproduction. What then,
keeps ghost shrimp from getting enough babies back each year? We measured how many ghost
shrimp babies came into Yaquina Bay from the ocean last year. We didn’t find as many baby ghost
shrimp on the mudflats as we expected from the numbers that came in from the ocean. We want to
know how many of those babies are still alive. (They would be no greater than 10 mm in carapace
length). The babies could be dying on the mudflats after surviving for several months in the ocean
but sampling for them takes many hands. We would be delighted if you would help us with some
of the work.
If you find lots of babies, we will know they aren’t dying on the mudflats and that
something is getting them before they get to the mudflats. If you find only a few babies or none,
something is getting them after they settle on the mudflats. Since more babies are expected where
there are more adults, we have to collect adult shrimp at the same time as babies to correct for their
different expected abundances.
Although it is rare, we also want to look for the ghost shrimp parasite to see how abundant
it is on the baby ghost shrimp. Maybe the ghost shrimp’s parasite is causing them to die when they
young. We can answer this second question by comparing how frequently baby shrimp are infested
compared to the adults. Since the ghost shrimp parasite is rare, we need to examine lots of babies
and adults to find it and see the pattern. We need many hands for this too and again, hope you will
help us.
Field sampling:
From the HMSC campus, with the right equipment, and a tide less than + 2 feet (for mud
shrimp) or +3 feet (for ghost shrimp), it takes about 45 minutes to get a dozen or more of either
species of shrimp. Everyone should be prepared to get muddy and WILL get muddy! Bring rain
gear and boots or tennis shoes that can still be tightly laced and sacrificed. Full rain regalia is best
on rainy days. Baseball caps are good to have under rain hoods on windy, rainy days. Rain pants
with knee boots or hip waders work well on sunny days. Clothes can be changed in HMSC
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restrooms. Total crisis immersions, that are muddy head to toe, possibly, can be addressed in our
single showers. The gentlest way to collect shrimp is to pump water into the mud and wash them
out. A special pump is needed for this and this is also one of the the most destructive ways to
sample mudflats. Clam guns make great corers. They are especially effective where one core can
be taken from the bottom of a previous core. Digging with shovels or cores is less destructive and
most shrimp recovered by these methods are in good condition. Shrimp slurpers also work but
often damage the shrimp, suck off their parasites and have a bias for the larger shrimp. The size
bias of slurpers makes them less valuable for most population samples but they are also least
destructive to the mudflats.
Lab observations:
Shrimp:
Measurements using calipers should be accurate to 0.5 mm. Burrowing shrimp lengths are
estimated relative to carapace length rather than by the length of their outsreached bodies. A data
sheet is attached. The way to measure carapace length is indicated at the top of the data sheet.
Sometimes we have pre-printed data sheets to use. A spread sheet is also available, as an example,
that has data from another class already entered. The estimates and graphs below are from the
spread sheet. Click the graphs on the spread sheet to see what data they are based on and then click
the data to see how the calculations were made.
Every specimen has a unique ID number. Then, across the top of the data sheet are columns
for “Ghost”, “Mud”, (the species of shrimp), “Sex” [the sex of the shrimp - see instructions],
“Carapace length”, (the distance from the forward tip to the back edge of the rostum to the back
edge carapace [see picture on the data sheet]) “parasite” (whether there is a bulging infestation
under either side of the carapace), “digging method” (sample collection method [shrimp slurper or
core]). Place every specimen with any of their parasites in a separate food cup with a snapped on
lid. Numbers on the first data sheet are 1-39. The second sheet numbers should be #40 - #79 etc.
Observations:
Parasites:
The eggs and gonads of the Upogebia and of the Orthione are easy to observe. The color of
their eggs tells about what stage of development they are in. Note on the data sheets: Carapace
length (in mm), sex (M, F), presence (=1) or absence (=0) of eggs. For Orthione, we will note their
presence, length and width (in mm), presence or absence of eggs (0 or 1) and color of eggs, length
of male (in mm), and presence of clams (0 or 1), Notes are for colors of shrimp eggs or isopod eggs
and for other commensals and parasites (write small but clear). We see lots of isopods on mud
shrimp and few on ghost shrimp.
The commensal clam, Neaeromya rugifera, is commonly found attached to the abdomen of
mud shrimp. Another isopod, Phyllodurus abdominalis fastens to the mud shrimp pleopods. This
isopod, P. abdominalis, is common in Washington and California but has been found in Oregon
only twice, both times from Yaquina Bay. This latter parasite would be a noteworthy find.
Data analyses:
Possible ways to compare these data include - Host size frequencies, parasite size
frequencies, parasite size with host size, host sex and size with parasite size, parasite size with
position on host, sizes of hosts with and without parasites.
Some of the major questions we are interested in include:
1. Are the isopods host limited (isopod sizes correlated with host sizes)
2. Are the isopods mate limited (fewer than expected pairs of isopods on hosts) (Can test with
binomial probability.)
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3. Are the male and female shrimp equally infested? (Compare the numbers of isopods on male and
female shrimp.)
4. Do all sizes of isopods produce eggs? (Compare brooding isopod sizes with other isopod sizes).
5. How does the frequency of egg bearing isopods change among host sizes?
Data analyses:
The attached spread sheet has “Ghost shrimp” and “Mud shrimp” work sheets. These
shrimp were collected on 8 April 2011 from the mudflat between HMSC and the OSU Wecoma
Pier, Yaquina Bay, Oregon. Scientists analyze data to “see” things. What can we see from the 8
April samples? Nearly all of the shrimp were collected by pumping water into the sand and
washing them out. The pump and fire hose etc. needed for this is pretty involved. Of the 279 ghost
shrimp we collected, 107 were male, 152 were females and few were infested by the native isopod
parasite of ghost shrimp, Ione cornuta.
The first two graphs compare size frequencies of male and female ghost shrimp and the
patterns of egg development with female size.
Number of shrimp
35
30
25
20
15
10
5
0
5
10
15
20
25
Carapace Length (mm)
Females
Males
Figure 1. Numbers of shrimp by different arapace lengths of male and female ghost shrimp.
Note that there are more female than male ghost shrimp apparent in figure 1. Is this due to
sex change or to differential mortality rates? Also, the 5-10 mm range in figure 1includes the new
shrimp that came into the population in 2010 (the babies). These new babies are about 3.9 % of the
total population however, the ghost shrimp populations of Yaquina Bay have been declining at
around 26% per year since 2002. Are the new babies abundant enough to replace the lost adults?
Note (Figure 2) that the average females bearing eggs with eyes are the largest size class.
The estimated means are on the spread sheet. In which part of the larval production season do you
think these shrimp were? The next figures are the mud shrimp collected at the same place and time
and by the same methods as the ghost shrimp.
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Number of Shrimp
12
10
8
6
4
2
0
5
10
15
20
25
Carapace Length (mm)
None
Early
Developing
Eyes
Figure 2. Number of female ghost shrimp per carapace length with no eggs, with early
development eggs, with developing eggs and with eggs that contain larvae developed far enough to
see their eyes “eyes”.
Number of shrimp
4
3
2
1
0
5
10
15
20
25
30
Carapace Length (mm)
Females
Males
Figure 3. Numbers of mud shrimp by sex with carapace length.
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Only 17 mud shrimp were collected on 8 April, compared to 279 ghost shrimp. Figure 3 is
therefore more difficult to look at but still, males and females were nearly equal. Note how
different the sex ratios are in figures 1 and 3.
Orthione frequency
3
2
1
0
5
10
15
20
25
30
Upogebia Carapace Length (mm)
Figure 4. The numbers of triple, double, single and unfested mud shrimp length.
From figure 4, which mud shrimp lengths were uninfested and which lengths were most
infested? What might cause this pattern?
Figure 4 is based on only 17 shrimp. These 17 mud shrimp contained 19 parasites. The 279
ghost shrimp contained only 3 parasites. The mud shrimp parasite was recently introduced to
North America from Asia. The ghost shrimp parasite is a native species. Why might there be such
a great difference in how intensely each species is infested?
Figure 5 is an application of binomial distributions (the statistics of flipping coins), which
gets a partial explanation in Excel applications by hitting F1 and then looking up “BinomDist”. The
parasites have to have a male and female to mate. The “expected” random frequencies (broken red
line) of (figure 5) does not coincide with the observed frequencies of infestations (solid blue line).
That means that parasites did NOT settle randomly among these mud shrimp hosts. The double
infestations deviated the most from random. Why might double infestations be more frequent than
single or triple infestations.
5
8
7
Frequencies
6
5
4
3
2
1
0
0
1
2
3
4
5
6
Orthione/Upogebia
Observed
Expected
Figure 5. The expected and observed frequencies of uninfested, single infested, double infested,
triple infested and quadruple infested mud shrimp.
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