Crab Study

Since its itroduction to the New Jersey shore in 1988, the western Pacific shore
crab Hemigrapsus sanguineus has spread to inhabit rocky intertidal locations
along the Atlantic coast from Massachusetts to North Carolina (McDermott 1998).

Many reasons have been proposed to explain the rapid spread of this non-indiginous
species. For example, it has been shown that H. sanguineus has longer spawning
periods along the mid-Atlantic coast than it does in its natural habitat in the
western Pacific Ocean, due to a more favorable climate (Epifanio et al 1998).

For this reason, these crabs are able to spawn more times per season than
indigenous crabs, providing one possible hypothesis for their population
explotion. For this species to expand its range along the Atlantic coast, it
will need to have wide tolerances to temperature and salinity. In 1998 Epifanio
found that The purpose of this study is to show the tolerance and behavioral
responses of H. sanguineus to varying water and air temperatures, and water
salinity concentrations. It is believed that these crabs will be very tolerant
to the various extreme conditions that they will be put through. It is the
ability of these crabs to survive in these unfavorable situations that is key to
their success. This experiment was also designed to prove the hypothesis that
the tolerance of H. sanguineus to various environmental factors increases with
size. METHODS AND MATERIALS- In February 2000, a field trip was taken to Crane

Neck Point to collect live specimens for the experiment. The field trip was
conducted at low tide. The water temperature was approximately 3 degrees Celcius,
with the air temperature slightly above freezing (0-1 degree Celcius). Live
crabs were obtained by overturning rocks in the intertidal zone. Hemigrapsus
sanguineus was found at all levels of the intertidal zone, although their
numbers increased as one moved toward the waterline. The crabs were collected
with no distinction toward size. The sizes of the specimens collected were found
to range from 0.5 to 4.2 cm. The crabs were collected in a plastic five gallon
bucket. Water was added to the bucket to keep the crabs from dehydrating. The
crabs were taken back to the lab, where they were kept in the plastic five
gallon buckets for a few weeks until the experiment began. Air hoses were added
to the buckets in order to oxygenate the water. The water was changed, as
necessary. The first experiment conducted was the experiment regarding water
temperature and salinity tolerances. The objective was to conduct an experiment
that would provide measurable data on the tolerance of H. sanguineus in various
water salinities, over a range of temperatures. To conduct this experiment, 8
one gallon acrylic tanks were obtained. Four were used for the cold temperature
experiment, and four were used for the room temperature experiment. Next, water
of varying salinities were produced. We started with seawater that had a
salinity of 30 parts per thousand. To obtain water with a salinity of 15 parts
per thousand, the sea water was slowly diluted by adding tap water. The water
was added slowly, and frequently checked with a salinity refractometer until the
desired salinity of 15 parts per thousand was obtained. The water was further
diluted, using the method above, to obtain the 5 parts per thousand water. To
obtain the water with a salinity of 40 parts per thousand, the 30 parts per
thousand sea water was again used, but this time was left uncovered as to allow
for water evaporation. After several days, and frequent testing with the
salinity refractometer, the water had a salinity of 40 parts per thousand. The
containers of water were covered with plastic wrap, as to prevent evaporation,
and keep the salinities constant. In additional a layer of mesh was used to
cover the top of each container, to prevent the crabs from escaping (Figure 1).

Four of the containers were left to stand at 25 degrees Celcius, while the
remaining four were placed in the deli case at a temperature of 5 degrees

Celcius. An air hose was added to each of the containers, in order to oxygenate
the water. Ten crabs, of a varying range of sizes, were added to each container.

The crabs, once again, ranged in size from 0.5 - 4.2 cm. In the first trial 15
fish food pellets were added to each container in order to provide the crabs
with food, and hopefully reduce cannibalism. This was repeated a second an third
time for both the 25 degree Celcius and 5 degree Celcius experiments, with the
absence of fish food pellets. The next experiment that was conducted