Animals: Crabs
(Pachygrapsus)
Methods
- three tanks, one freshwater, one 17.5% salinity,
and one 35% salinity
ari
Changing Salinity and Its Effects
on Marine Organisms
Conducted By: Sarah Fox, Christopher Ho, Mackenzie Lighterink, Allison Vu
- 15 minute assimilation period, then a brick was
placed in each tank with 30 minutes of observation
Methods
- three freshwater petri dishes, three with 17.5%
salinity, three with 35% salinity
- 80 mL of liquid per dish
- 5000 mL of liquid per tank
- seven crabs per tank
Plants: Duckweed
(Lemna Minor)
Abstract
Salinity is a critical aspect of seawater composition that affects the water's capacity to support
marine biodiversity. Ice melt, rising ocean levels, and changes in precipitation have caused ocean
salinity levels to fluctuate. Experiments were conducted to investigate how changes in salinity might
impact aquatic ecosystems. Pachygrapsus crabs were placed in tanks of salinities varying from salt to
fresh water. The crabs could withstand salinity changes even at 50% their normal levels, though they
experienced stress. They could not, however, tolerate freshwater. Also tested was Lemna Minor’s
(duckweed) reaction to increasing salinity levels up to 100% seawater. More duckweed perished as
salinity levels rose. These results support the hypothesis that any dramatic dilution of seawater would
disrupt marine communities. Further research is needed to determine if salinity changes would influence
other species in a similar manner as it did the Pachygrapsus and duckweed.
- 50 duckweeds per dish
- Observe for five days
Introduction
Anthropogenic emissions, namely carbon dioxide, have led to a unprecedented rise in global
temperature. Commonly referred to as global warming, this climate change has led to glacial melt,
weather anomalies, and other detrimental effects. This crisis has led to significant shifts in ocean
composition. Chief among them is salinity, the amount of dissolved salt in ocean water. We were
interested in how such drastic changes might affect organisms who are accustomed to certain salinity
levels.
Data: # of Living Duckweed
Data: # Crabs on the Brick
Discussion Analysis
Discussion/ Analysis
- In the freshwater tank, the crabs were incredibly
uncomfortable and tried to scramble up the walls. Once
the brick was introduced, the crabs settled onto the rock
and began to osmoregulate by spitting water out their
mouths.
- This shows the extreme stress on the crabs and the
strain on their bodies to remove the excess water.
- In the 50% seawater tank, the crabs slowly climbed
onto the brick and were less frantic. In the pure
seawater tank, the crabs were incredibly calm, and only
occasionally perched on the brick.
- These results support our conclusion that a change in
salinity would stress the osmoregulation of our crabs,
Pachygrapsus. For future experiments, we would want
to increase our sample size and use other varieties of
marine life as well.
Conclusion
From our research, we were able to conclude that both increasing and decreasing water salinity
negatively affected our sample species. Our saltwater species, the Pachygrapsus crassipes, showed
greater physical discomfort in freshwater and lower salinity conditions, driving the crabs out of the water
to a representative land habitat. Similarly, our freshwater species, Lemna minor, experienced greater
mortality rates after exposure to higher salinity waters in comparison to the freshwater control. While
these findings only represent the effects on two of the many water dwelling species, it still provides
evidence of the potential damage that salinity changes could have on water based ecosystems. Further
research in a variety of other species is needed to assess the global effects of an ocean with greater
salinity extremes
Acknowledgements
We thank Mr. Stephen (Chase) Hightower for his lab assistance and Dr. Ngai Lai for his help in lab
setup and experimental design.
- We initially attempted the duckweed experiment
with a three day observation period, but did not see
significant results within that time frame.
- We reset our experiment with new duckweed and
observed them for five days. As expected, the
duckweed in pure seawater suffered the most deaths,
while the freshwater group in large part stayed
healthy and green.Duckweed cells are turgid at 0% salinity. Our results
confirmed that an increase in salinity will cause water
to rush out of the duckweed, dehydrating the plant
and killing it within days.
-These findings are alarming considering the
changing salinities associated with global climate
change. Duckweed would not be able to survive and
freshwater ecosystems would be altered if such
salinity increases were to occur.