Saddleback Journal of Biology - Saddleback College

hemolymph concentrations were hyperosmotic to the
media in which the crabs were kept and significantly
different from each other. Brown and Terwilliger
(1992) carried out a similar study on Dungeness
crabs (Cancer magister) and obtained the same
results. Susanto and Charmantier (1999) worked with
a freshwater crustacean -- crayfish Astacus
leptodactus; their experiment demonstrated that
hemolymph concentarions of A. leptodactus were
hyperosmotic to experimentally increased salinities
of water up to 13‰ salinity and isoosmotic at higher
salinities up to 21‰.
The present study examined osmoregulation
in green shore crab (Hemigrapsus oregonensis),
which inhabit intertidal zone, at three different
salinities of water: approximately 33‰, 20‰, and
10‰. It was hypothesized that at three different
salinities hemolymph osmolalities of H. oregonensis
would be hyperosmotic to the surrounding medium
and significantly different from each other.
Materials and Methods
H. oregonensis were collected at Doheny
State Beach, Dana Point, CA. In the laboratory the
crabs were divided between two glass containers with
water about 6 cm deep; the containers were set into
an aquarium with gravel. Over the course of the
experiment, the water in each container was aerated
and kept at room temperature (20° C). First, H.
oregonensis were placed into 33‰ salinity water.
Crabs were allowed to acclimate for 24 hours; after
that samples of hemolymph were collected from each
crab. The same procedure was repeated after
transferring the crabs into water of approximately
20‰ salinity, followed by transferring the crabs into
Hemolymph Osmolality (mmol/kg)
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Spring 2010 Biology 3B Paper
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water of approximately 10‰ salinity. Thus, 3 rounds
of hemolymph samples at three different salinities of
water were collected.
A 27 gauge syringe was used to collect
hemolymph. The needle of a syringe was inserted
through the membrane of the last walking leg, and 10
µL of hemolymph were removed. Osmolality of
hemolymph samples was measured with a Wescor
vapor pressure osmometer.
Desired salinities of water were achieved by
diluting 33‰ salinity water with distilled water in the
appropriate proportion. A sample of water of each
salinity was taken after 24-hour acclimation period,
and osmolality of water was measured. Upon
completion of the experiment the crabs were released
back to their natural habitat.
Results
The mean osmolality of water of
approximately 33‰ salinity was 1058 mmol/kg ±
13mmol/kg (±SEM, N=2); the mean osmolality of
hemolymph of H. oregonensis acclimated to this
salinity was 955 mmol/kg ± 14.3 mmol/kg (±SEM,
N=8), which was hypoosmotic to the surrounding
medium. The mean osmolalities of water of
approximately 20‰ and 10‰ salinities were 645
mmol/kg ± 1 mmol/kg (±SEM, N=2) and 312
mmol/kg ± 8 mmol/kg (±SEM, N=2) respectively;
the mean osmolalities of hemolymph of the crabs
acclimated to these salinities were 882 mmol/kg ±
9.20 mmol/kg (±SEM,N=11) in 645 mmol/kg water
osmolality and 724 mmol/kg ± 57.3mmol/kg (±SEM,
N=10) in 312 mmol/kg water osmolality, both of
which were hyperosmotic to the surrounding
medium(Figure 1) .
1058 645 312
Water Osmolality (mmol/kg)
Figure 1. The mean osmolalities of hemolymph of H. oregonensis acclimated to three different water osmolalities.
Error bars indicate standard errors of the mean.
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Saddleback Journal of Biology
Spring 2010