The Effects of Ocean Acidification on Hyas lyratus

1
The Effects of Ocean Acidification on Hyas
lyratus Metabolic Processes
1, 2 Elena Fernandez 08 and 3 Dr. Sherry Tamone
1Kenyon College Dept. Of Biology, 2University of
Alaska Southeast REU Scholar 2007 3University of
Alaska Southeast Dept. of Marine Biology
Abstract
Recent studies indicate that increasing amounts
of atmospheric CO2 dissolving into the ocean
biome are causing acidification of the marine
environment. Some predictive oceanographic
models indicate that pH will drop up to 0.5 pH
units over the next 100 years. It is well
documented that ocean acidification inhibits the
ability of organisms to form and maintain calcium
carbonate structures. Examples of such organisms
are diatoms, mollusks, and crustaceans. The
physiological cost to crustaceans that must
regulate internal pH and must form a calcareous
exoskeleton during each larval, juvenile and
adult molt cycle remains unclear. We measured
standard metabolic rates of female lyre crabs,
Hyas lyratus that were acclimated for one week at
pH 8, pH 7.5, pH 7.0, and pH 6.5. Metabolic rates
were significantly different between crabs held
at pH 8 and pH 6.5 (0.55 vs. 0.43 ml O2/kg/min).
Enzymatic rates of lactate dehydrogenase (LDH),
pyruvate kinase, and citrate synthase decreased
significantly with decreased pH. This decreased
activity of LDH could be detrimental to
physiological processes that require anaerobic
metabolism. In fact, increased mortality was
observed in crabs that were acclimated to pH 7.5,
pH 7.0 and pH 6.5 and exposed to hypoxia for 24
hours when compared with control crabs held at pH
8.0. It is likely that there is an energetic
cost to crabs associated with ocean acidification
and that this cost could have a negative impact
on energetically costly physiological processes
such as growth and reproduction.
Take Home Message and Future Directions
Introduction
The worlds oceans function as a carbon sink. As
atmospheric CO2 levels rise, the equilibrium of
the marine carbon cycle is unbalanced and more
carbonic acid is formed as a result1. This causes
marine pH to decrease leading to ocean
acidification. Modeling studies have shown that
marine pH will decrease about 0.3-0.5 units every
100 years at the current rate of increasing CO2
levels in the atmosphere2,3. The increasing
acidity has been shown to inhibit the production
of shells in certain marine organisms (pteropods
and arthropods), as well as coral bleaching4,5.
It is possible that populations of commercially
harvested species will be adversely affected by
this added stressor, causing a potential economic
crisis for the fishing industry. Studies have
shown that invertebrates cannot effectively
acclimate to acidic conditions, potentially
adversely affecting overall metabolism6,7,8. It
is also possible that metabolic enzymes could
also show decreased activity in acidic
conditions, as enzymes have a narrow range of pH
levels in which they function. These studies
were conducted to investigate the potential
influence of pH on metabolic rates. Our model
organism was the lyre crab Hyas lyratus, a
relative of the commercially important Majid
family of crabs Chionoectes biardi and C. opilio.
Crabs will be exposed to view the effects of a
gradient of environmental acidifications on
overall metabolic rate as well as metabolic
enzyme activity.

• Overall change in SMR was significant when
  exposed to lowered pH.
• All metabolic enzymes demonstrated a significant
  decrease in enzyme activity in acidified samples.
• A number of potential studies could build on this
  research to gain a better understanding of the
  mechanism underlying decreased pH on metabolism.
  Possible research topics include the response to
  anoxic stress under acidified conditions, a
  comparative metabolic enzyme study of shallow and
  deep water crabs exposed to acidic conditions,
  and hemolymph buffering capacity of different
  crab species acclimated to lower environmental
  pH levels.

Questions and Hypotheses
Results

• Does acidification show a significant effect on
  the standard metabolic rate (SMR)?
• Hypothesis There will be a significant increase
  in standard metabolic rate of crabs exposed to
  lowered pH.
• Which metabolic enzymes (PK, LDH, CS) does ocean
  acidification significantly affect, and how?
• Hypothesis There will be significant
  upregulation of metabolic enzymes as the
  environmental pH decreases.

Acknowledgements

• ASLO for allowing me to present at todays
  conference.
• NSF and NOAA for project funding.
• University of Alaska Southeast, specifically Dr.
  Sherry Tamone, Dr. Matt Heavner, and Beth
  Mathews.
• The crabs for their sacrifice. May they rest in
  peace.
• University of Alaska Fairbanks graduate students
  for their literature help, fishing trips, and
  entertainment in and out of the lab.
• REU comrades for their ideological support and
  the adventure of a lifetime.

Methods Organism Capture and Husbandry

• Ovigerous females captured using crab pots off
  Spuhn Island, Juneau, AK.
• All crabs were fed herring twice a week ad
  libidum and allowed to acclimate to tanks for one
  week. Baseline standard metabolic rate (SMR) was
  determined using a YSI oxygen meter in a closed
  system.
• Carbon dioxide bubbled into test tanks to
  decrease pH to either 7.5, 7.0, or 6.5. One tank
  was kept at ambient pH and used as a control.
• All organisms were allowed to acclimate to
  acidified conditions for one week prior to
  testing.

Works Cited

• Herzog, et al. Environmental Impacts of Ocean
  Disposal of CO2. Energy Convers Mgmt. 376-8
  (1996) 999-1005.
• Pelejero, et al. Preindustrial to Modern
  Interdecadal Variabilty in Coral Reef pH.
  Science. Vol. 309 (2005) 2204-2207.
• McNeil and Matear. Projected climate change
  impact on oceanic acidification. Carb. Bal.
  Mgmt. 12 (2006).
• Feeley, et al. Impact of Anthropogenic CO2 on
  the CaCO3 System in the Oceans. Science. 305
  (2004) 362-366.
• Pala. A World Without Corals? Science. 316
  (2007) 678-681.
• Spicer, et al. Influence of CO2-related seawater
  acidification on extracellular acid-base balance
  in the velvet swimming crab Necora puber. Mar
  Biol. 151(2007)1117-1125.
• Miles, et al. Effects of anthropogenic seawater
  acidifiction on acid-base balance in the sea
  urchin Psammechinsu miliaris Mar. Poll. Bull.
  54(2007) 89-96.
• Pane, Eric and James Barry. 2007. Extracellular
  acid-base regulation during short-term
  hypercapnia is effective in a shallow-water crab,
  but ineffective in a deep-sea crab. Marine
  Ecology Progress Series. 334 1-9.

SMR and Enzyme Assays

• Crab weighed and placed in metabolic chamber for
  80 minutes.
• Measured change in oxygen over the allotted
  period of time.
• Animals were sacrificed and gill and muscle
  tissue samples taken from carcasses.
• LDH, CS, and PK enzyme activity were measured
  using known protocols.