The Effect of Rising pH Levels on Marine Organisms in Tide Pools
Jessica Garcia and Jackie Olvera
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
Abstract
Marine organisms are being affected by the acidity of the ocean. The
hypothesis tested was that there would be a less abundance of animals in an environment
with a higher acidity. Two locations in Southern California were observed: Doheny State
Beach in Dana Point and Treasure Island in Laguna Beach. The average pH at Doheny
was 8.2 and the average pH at Treasure Island was 8.8. The variation in pH was too
slight to see a difference in abundance of organisms. The area of the tide pools however
did have an affect of abundance of marine organisms. At Treasure Island the tide pools
were much deeper therefore they had significantly more organisms than that at Doheny.
We concluded that to see if the acidity of the ocean does in fact have an effect on the
abundance of organisms then a wider range of locations would be needed to be observed.
More organisms were found in the larger tide pools which was expected so in order to
have more accurate results we would need to visit tide pools that were much closer in size
at all locations.
Introduction
Recent studies have shown that the rise in carbon dioxide levels in Earth’s
atmosphere has had an effect on Ocean acidity. When carbon dioxide in the air hits the
ocean water a chemical reaction occurs and turns that carbon dioxide into carbonic acid.
An abundance of Carbon Dioxide changes the chemistry of the sea causing the life for
most marine organisms to be in danger (Caldeira 2003).
The distribution of animals is correlated with the environmental factors such
as dissolved oxygen (Jayalakshmy 2008), water temperature, depth, tidal amplitude, and
turbidity (Cha 2004). Water temperature and acidity are directly related. As the water
temperature increases the pH of the water becomes more acidic. The carbonic acid
present in intertidal environments has a negative effect on its inhabitants. Most marine
organism shells and skeletons are composed of the mineral calcium carbonate which is
slowly dissolved by the carbonic acid (Caldeira 2003). Therefore the higher the water
temperature and the more carbon dioxide polluted into the air leads to a more acidic
ocean that can dissolve the shells and skeletons of marine organisms that play an
important role in the food chain. For example smaller shelled organisms called pteropods
are becoming rarer which can disrupt the food chain. Pteropods are a major food source
for larger organisms such as fish and lobsters which are a major food source for humans
(Caldeira 2003). Temperature cannot be controlled as easily as carbon dioxide
abundance. The solution to this problem is to simply lower carbon dioxide emissions. If
we continue to emit carbon dioxide into our atmosphere, then the continuation of
dissolving shells and skeletons of marine organisms that are vital to the food chain will
quickly be eliminated.
Marine organisms already have other dangers to worry about such as
predators. For example in areas where starfish are more abundant sea urchins tend to
emigrate from that environment (Schroeter 1983). Most marine organisms are capable of
adapting to other environmental changes such as turbidity. Not only do shelled organisms
suffer from the rise in pH of the ocean but coral reefs are also struggling to survive
(Smith 1992). Scientists are considering ocean acidification as the other carbon problem
with the first carbon problem being global warming. The first step to solving this
problem is lowering the carbon dioxide emissions given off from automobiles. Doing
this can also help the ozone layer and ultimately halt the ocean acidity problem.
Methods & Materials
Observations were determined during low tide in November of 2009 for the
following two locations: Doheny State Beach in Dana Point, California and Treasure
Island Beach in Laguna Beach, California. The locations were selected by their
variations in pH levels. At each location three tide pools of various sizes (small, medium,
and large) was observed calculating the area for each using a tape measure. Having once
determined the area calculations of the tide pools, all organisms visible were counted
within each pool.
Determining the quantity of each organism found in the tide pools, allowed us
to foresee any possible differences that could potentially be affected due to its levels of
pH. Among the organisms discovered were the Amthopleura xanthogrammica (sea
anemone), Pisaster ochraceus (sea star), Mytilus californianus (California mussel),
Pagurus samuelis (hermit crab), Tegula funebralis (snail), Octopus vulgaris (common
octopus), and Aplysia californica (sea hare). The pH at both locations was determined by
using a pH probe provided by Professor Steve Teh, Professor of Biological sciences at
Saddleback College.
Results
In Table 1, the frequency of organisms was graphed according to their
location and size of tide pool they were located in. This indicates that organisms were
more abundant at the tide pools located at Treasure Island, specifically in the large tide
pool.
In Table 2, the amount of each individual species observed was graphed along
with the pH of the tide pool it was located in. The results indicated that there was a
difference in the abundance of organisms located in tide pools with different acidity
levels. The average pH of the tide pools located at Doheny State Beach was 8.2 and the
average pH of the tide pools located at Treasure Island was 8.9. There was a difference
in the abundance of organisms at both locations due to there varying pH levels. More
organisms were found in the tide pools at Treasure Island than at Doheny State Beach.
Table 1
60
Mean Frequency
50
40
Doho
30
T.Isle
20
10
0
Small
Medium
Large
Table 1 caption: Bar graph displaying the mean frequency of marine organisms in tide
pools at the locations of Doheny State Beach (Doho) and Treasure Island (T. Isle).
Table 2
250
Sea Anemone
200
Frequency
Mussels
Snails
150
Hermit Crabs
100
Starfish
Sea Slug
50
Octopus
0
8.2
8.9
pH
Table 2 caption: Bar graph displaying the amount of total organisms of a specific species
found in different levels of pH.
Discussion
The acidity level in intertidal environments has been shown to have a negative
effect on shelled organisms. Shells are beginning to slowly dissolve due to the acidity of
the ocean which is created by the carbon dioxide emissions given off by various creations
made by the Industrial Revolution. We tested this by measuring the pH of marine
environments at two different locations in Southern California. Along with the pH
readings we counted the amount of organisms present of different species. The species
included were sea anemones, mussels, snails, hermit crabs, sea stars, sea hares, and
octopus. The area of each tide pool was also conducted by measuring length, width, and
depth.
Our results indicate that our hypothesis was supported however the difference
in the abundance of organisms found in the different pH environments was too slight to
make an assertive decision with confidence. The area of each tide pool indicated that
there was a more abundance of marine organisms living in larger environments. Further
investigation is required in order to justify these results with confidence.
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