Download Ocean Acidification and the impacts for

Erica Evans
EV128
Ocean Acidification and the impacts for Northeast Pacific fisheries in relation to the California
Current System
Introduction
Our climate has been changing more rapidly in the past 200 years than it ever has during
our presence as a species on earth (Karl & Trenberth 2003,1720). Humans, through the burning
of fossil fuels and greenhouse gas emissions, have been the main driver of climate since the
beginning of the industrial revolution (Karl & Trenberth 2003, 1720). Burning of fossil fuels has
increased greenhouse gas emissions by more than a third when contrasted with pre-industrial
levels (Barnosky et al 2012, 54). This increase is linked to rising temperatures, changing ocean
chemistries, and shifts in terrestrial and marine ecosystems (Barnosky et al 2012, 56-57;
Ainsworth et al 2011, 1217).
Changes in ocean chemistry can have profound ecological and economic impacts. Oceans
are one of the most important regulators in the earth’s biogeochemical cycle, and provide habitat
for an enormous number and diversity of species. Ocean acidification is caused by the uptake of
CO2 into marine ecosystems, and contributes to the impacts of climate change by decreasing pH
and changing carbonate saturation levels (Zeebe 2012, 141-143; Logan 2012, 820-821).
Changing pH and carbonate saturation levels contributes to the degradation of populations of
calcifying organisms, and declines in many fisheries (Ainsworth et al 2011; Orr et al 2005). This
paper will focus on the impacts of ocean acidification on fisheries in the Northeast Pacific,
centering on the degradation of both fish and oyster hatcheries in relation to changes in the
California Current System (CCS). This paper will also discuss recommendation for future
research into the physiological effects of ocean acidification on fished populations.
1
Chemistry
Oceans are the largest sinks of inorganic carbon in the carbon cycle. From 1750 to 2000
the oceans absorbed approximately one third of anthropogenic atmospheric carbon (Baird et al
2009, 460, Logan 2010, 819). CO2 concentration in the atmosphere has increased by ~40% since
the beginning of the industrial era (Zeebe, 2012, 142). The absorption of carbon into the ocean
system has resulted in a net decrease in oceanic pH. Since the late 18th century, mean surface
ocean pH has dropped from 8.2 to 8.1, a change roughly equivalent to a 30% increase in
hydrogen ions (Logan 2010, 819). The pH levels have not dropped below 8.1 during the past two
million years (Raven et al 2005, 1; Calderia 2003, 365). If current trends continue we can expect
to see pH drop by another 0.3-0.4. This drop would be roughly equivalent to a 150% increase in
hydrogen ions (Logan 2010, 819).
Oceans act as a buffer for CO2 in the atmosphere by absorbing CO2 and converting it into
carbonic acid (H2CO3), which breaks down into bicarbonate (HCO3-), carbonate (CO32-) and
hydrogen ions (Logan 2010, 819). These reactions can be reversed, to help prevent large-scale
changes in salinity. The reversal of these reactions is dependent on ion concentrations,
temperature, salinity and pressure. This directionally means that as oceanic chemistry adjusts to
accommodate for excess atmospheric carbon, it decreases in ability to buffer and regulate
oceanic acidity. When atmospheric CO2 is high, fewer carbonate ions are produced and the
ocean has a lower pH (Logan 2010, 819). Figure 1 demonstrates the relationship between
changes in alkalinity, photosynthesis, calcite formation and CO2 release.
Carbonate is essential for the formation and development of many organisms in the
oceans. We have seen a 10% decrease in carbonate concentration in the oceans since preindustrial times, with a predicted decrease of 50% by 2100 (Baird et al 2009, 460-461).
2
Decrease in carbonate concentration will have profound impacts across oceanic environments.
Calcifying organisms play a central role in oceanic ecosystems, and a decrease in their
populations will have compounding effects up the food chain (Baird et al 2009, 462).
Fig. 1
Figure shows the effects of
various processes on ocean
alkalinity and dissolved
inorganic carbon. Total
dissolved inorganic carbon
(TDOC) is changed
exclusively by invasion and
release of CO2, while
photosynthesis and respiration
change total alkalinity (TA).
CaCO3 formation and
dissolution affects both
TDOC and TA.
Source: Zeebe (2012, 145)
Consequences for calcification rates and fisheries
Impacts of acidification on Northeast Pacific fisheries
Acidification affects fisheries containing salmon, tuna and herring through population
and diversity losses lower down in the food chain, along with physiological changes (Belli 2012,
25; Gosling et al 2011, 447). These fish, along with marine birds, some whales, and seals depend
on pteropods as a major source of food. Ocean acidification limits the ability of pteropods to
form their shells by decreasing the availability of carbonate minerals (Belli 2012, 25).
Simulations from five Ecopath with Ecosim models, presented at the International
Symposium on Climate Change by Ainsworth et al, were used to analyze responses of the food
web in Northeast Pacific marine environments. These simulations considered five different
3
climate models and assessed the impacts of biomass change, un-fished functional groups,
ecosystem characteristics, and the state of the ecosystem in the 50th year of the simulation
(Ainsworth et al 2011, 1217).
Ecopath with Ecosim modeling (EWE) is a model system that combines the living and
non-living aspects of an ecosystem. This modeling approach incorporates thermodynamic
accounting to track the flow of energy throughout an ecosystem. The Ecopath model is the
initialization state for the Ecosim model, and represents a static point in time. The Ecosim model
uses two primary equations (fig. 2) to account for primary producers and consumers. In these
equations B𝑖 is the biomass of the prey and B𝑗 is the biomass of the predator. The parameters are
then used relate the production rate (P), ecotrophic efficiency (EE), the emigration of species in
and out of the ecosystem (E), the growth efficiency (g), the immigration rate (I), natural and
fishing mortality (M) and (F) and the number of functional groups (n) (Ainsworth et al 2011,
1218).
Fig. 2
Equation 1 accounts for
primary producers, equation 2
for consumers.
f() is the functional
relationship used to predict
consumption rates.
Source: Ainsworth et al 2011,
1218
Factoring in primary production changes, zooplankton size, dissolved oxygen, ocean
acidification effects, and range shifts, coupled with all the climate effects together “reduces
landings by 77% under the moderate climate effect strength scenario and by as much as 85%
under the severe climate effect strength scenario” (Ainsworth et al 2011, 1223). This modeling
4
simulation showed that shifts in range are the dominant effect of climate change as a factor in
decreasing fish populations.
These modeling simulations, while fairly general, can give us insight into the future of
fisheries in the Northeast Pacific region. We can predict that 1) some fisheries and species will
increase while others will decline, 2) fisheries and species will not respond uniformly over all
areas, 3) interactions between the variable effects of climate change in different regions will
result in a greater variety of changes in fisheries when compared to one effect alone (Fig 3).
While some species may experience positive growth, we can hypothesize that fisheries generally
suffer as a result of climate change. Fished species tend to experience greater losses than unfished species (Ainsworth et al 2011, 1226).
Fig 3
Averaged values across all EWE
models showing projected fish
landings for biomass and
projected fish landings for the
year 2060. Baseline numbers
represent landings and biomass
numbers without climate change.
Error bars represent the range of
values predicted using moderate,
conservative and substantial effect
sizes.
Source: Ainsworth et al 2011,
1222
5
Studies have also shown links between physiological changes in fish populations and
ocean acidification. There are connections between ocean acidification and impaired inner ear
development (Checkley et al 2009, 1683), sensitivity to predation (Munday et al 2010, 1850),
and alterations in olfactory sensing (Munday et al 2009, 1-3). There is also evidence that
acidification leads to decreased cellular activity and respiratory function. These decreases can
lead to increased mortality in fish populations (Raven et al 2005, 19). These changes could have
profound impacts by altering ranges and habitat niches across fish populations.
It is difficult to predict what will happen economically to affected fisheries, as we can
only view economic balance within our current economic framework. Such frameworks are
highly limited when applied over centuries or decades. It is also possible that losses in
production will be offset by increases in price of the commodity, as decreasing production levels
on a global scale will drive up prices in all markets. When assessed within the context of rapid
shifts in consumer tastes and interests, it is likely that markets will adjust to variations in
production levels (Quesne et al 2011, 340). Fisheries can also be managed to avoid the effects of
climate forcing on fished populations. The sensitivity of fished populations can increase with
exploitation, indicating that more informed management practices could reduce the risk of largescale impacts (Perry et al 2010, 19).
Impacts of ocean acidification on calcifying organisms and Northeast Pacific oyster
hatcheries
Ocean acidification affects oysters and other marine-calcifying organisms. Ocean
circulation patterns, especially along the west coast of the United States make these areas
particularly susceptible (Belli 2012, 24). The upwelling of cold bottom currents into shallower
shore areas brings acidified chemistry, along with reduced saturation of carbonate (McPhaden
6
2006, 1740). This water can have a pH as low as ~7.5, in contrast to usual pH levels ~8.2. This
cold acidic water is pulled into hatcheries where it inhibits the growth of calcifying organisms.
The ability of oysters and other shellfish, lobsters, clams as well as planktons and corals to build
their shells is related to saturation levels (Belli 2012, 25).
Saturation is the amount of carbonate mineral dissolved in a body of water. Saturation is
not evenly distributed throughout oceanic systems and is inversely related to the solubility of a
carbonate mineral. The coefficient of saturation is dependent on pressure, temperature and
salinity (Logan 2010, 820). The inverse relationship between solubility and saturation state
results in high saturation in warm shallow tropical waters and low saturation in colder deep
water. This reduction in carbonate minerals reduces the ability of many marine organisms to
develop properly (Service 2012, 147). When saturation levels equal 1, there is an equally likely
chance of dissolution as there is of carbonate formation. The saturation horizon is the plane in
the ocean below which saturation is less than 1 and above which saturation is greater than 1
(Logan 2010, 821). As oceans become more acidified, the saturation horizon moves upward,
making it increasingly difficult for carbonate-dependent organisms to develop (Logan 2010,
821). Laboratory experiments show a strong decrease in calcifying rates as pH decreases (Raven
et al 2005, 20).
Solutions are available on a local level, but function only as a piecemeal solution.
Shellfish farmers can monitor acidity and wind velocity to limit letting acidic water into
hatcheries, as well as filling tanks in the afternoon when waters have warmed (Service 2012,
147). The 2012 U. S. federal budget cut funds from several monitoring projects off the
Washington coast, reducing the effectiveness of these operations. It is also important to note that
these mitigating actions become increasingly less effective as ocean chemistry becomes more
7
uniformly acidic, and more and more of the water column becomes under saturated (Belli 2012,
24).
The California Current System
Modeling focusing on the California Current System (CCS) shows that following recent
trends, we will see rapid increases in under saturated waters in the top 60 meters of ocean. By
2050, California Current System waters will be under saturated during 50% of the year (Service
2012, 148; Gruber et al 2012, 220). Figure 4 shows projections for mean saturation rates
extending to the year 2064. These under-saturated conditions will pose extreme difficulties for
larval organisms developing at or near the surface. Approximately 73% of profits from the $3.8
billion a year US commercial fishing industry comes directly from calcifying organisms and
their predators (Denman 2011, 1019). While most US fisheries will be impacted by acidification
in some way, CCS upwelling will likely exacerbate this detrimental change in the Northeast
Pacific.
Fig 4.
Mean Saturation rates of
calcite (right y-axis) and
aragonite (left y-axis) in the
near shore regions of the
California Current System
(CCS), in relation to
atmospheric CO2.
Included are the mean
evolutions of the Tropical,
Arctic and Southern Oceans.
Source: Gruber et al 2012,
222
8
Mitigation
Even if anthropogenic CO2 levels were reduced to zero within the next few days, ocean
pH levels would continue to decrease for the next several decades. The under-saturated water
washing up along the coasts has been circulating for 30-60 years, and was therefore exposed to
CO2 levels at levels much lower than today. This indicates that waters exposed to higher levels
of CO2 are still circulating, and have yet to make their way into global current systems (Service
2012, 148).
Geoengineering has been suggested as a means to limit climate change and the resultant
impacts. Directly addressing ocean acidification would involve depositing 13 billion tons of
limestone into the world’s oceans annually, and is therefore not a feasible approach to mitigating
the acidification process (Logan 2009, 462). However geoengineering projects to limit or remove
CO2 are marginally more feasible and could affect ocean acidification indirectly. These
proposals center on climate engineering, or creating uniform reductions in incoming shortwave
radiation. These proposals involve injecting high volumes of aerosols into the atmosphere to
create large scale cooling effects. While this would not directly solve acidification, it could scale
back the effects by redistributing emissions and CO2 concentrations across land, oceanic and
atmospheric environments (Mathews et al 2009, 1,4).
The effects of acidification can be mitigated through the restoration of costal sea grass
areas. Sea grass stores CO2 in its roots, which helps to ameliorate the impacts of acidification.
Similarly, repairing mangroves, salt marshes and other coastal wetland areas can have a positive
effect on reducing ocean acidity (Belli 2012, 31). However, this will not be enough to remove
the entirety of the impact. Without regulation on atmospheric carbon, there will not be a
substantial decrease in acidification rate. Recommendations have been made to limit atmospheric
9
CO2 at 550 ppm because at levels above 550ppm aragonite becomes highly under saturated.
However 550ppm is probably too high to avoid other detrimental effects to marine ecosystems. It
is therefore recommended that atmospheric levels should be kept below 500ppm at the very
least, and below 450ppm following the precautionary principle (Turley et al 2010, 791).
Discussion and recommendations for future research
While most of the research referenced in this article is fairly conclusive, there remains
some debate about the ability of fished populations to adjust, the consequences for fished
populations vs. non-fished populations, as well as the physiological impacts of acidification on
fish.
Ainsworth et al (2011) indicates that fished populations will be worse off in global
climate change scenarios than non-fished populations, and that fishing acts as a stressor to
execrable the impacts of climate change. Quesne et al. (2011) found no discernable difference
between fished and non-fished populations in climate change scenarios. More research should be
undertaken into this area to discern if fishing acts as an external stressor.
There is also debate about the ability of populations to adjust to changes in range, diets
and acidification. Many species (particularly those dependent on calcifying processes) will
experience decreases in population (Orr et al 2005, 681, 685). However, many marine organisms
exist within flexible food webs, and can adjust diets and ranges in response to resource scarcity.
Studies in North Sea populations show species transitioning to drastically different diets in
response to environmental stresses (Quesne et al 2011, 336). It is unclear if other populations
will be able to make similar adjustments, particularly in fishery dependent areas.
Fished populations will not necessarily decrease uniformly. Increases in CO2 levels could
facilitate phytoplankton growth, thereby encouraging the growth of fish populations further up
10
the food chain. Any alteration to primary producers will have effects further up in the food web
(Quesne et al 2001, 337). However, analysis predicts that the trend for fished populations will be
generally negative (Ainsworth et al 1223).
Checkley et al (2009), Munday et al (2009), Munday et al (2009), and Quesne et al
(2011) indicate that decreasing pH can affect physiological functions of fish populations. While
the links between impaired inner ear development, olfactory capacity and ability to sense
predators are fairly understood, the extent of these links in the larger scale of populations is still
unknown.
Further research should be undertaken to help understand the ramifications of ocean
acidification on a large scale. While impacts are beginning to become evident in oyster
hatcheries, (Belli 2012, 24-25), we still do not fully understand what global changes will happen
to fish populations as our oceans become increasingly acidified.
Conclusion
Current literature displays the direct links between ocean acidification and
detrimental effects to fisheries and calcifying organisms. As the earth continues to warm, we will
see pH decreases far from what we have experienced as a species. It is important for the
scientific and political communities to be aware of the ramifications of climate change in the
context of ocean acidification (Baird et al, 2009). Acidification-created change in ecosystems
will affect fisheries and other ocean resources, leading to global economic impacts.
It is increasingly clear that an international consensus is needed on how to directly
mitigate runaway CO2 increases, as well as providing strategies for adaptation. While there is
general consensus in the scientific community, there has not been a policy consensus, or
11
movement towards implementation of law to reduce or mitigate the impacts of oceanic
acidification (Baird et al 2009, 462-464).
The United States’ market could shift away from dependence on fisheries, however many
undeveloped countries rely on fishing as a primary source of protein and income (Wittig 2012).
The interdependence of the world’s oceanic ecosystems makes an international solution
exceedingly important. We need to be able to reassess in a global context what comes next and
how to avoid the consequences of acidification. It is clear that without some form of international
regulation, we will continue to see the impacts of anthropogenic climate change and oceanic
acidification perpetuate into the future.
12
References
Ainsworth, C. H., Samhouri, J. F., Busch, D. S., Cheung, W. W. L., Dunne, J., & Okey, T. A.
(2011). Potential impacts of climate change on northeast pacific marine food webs and
fisheries. ICES Journal of Marine Science, 68(6), 1217-1228.
Baird, R., Simons, M., & Stephens, T. (2009). Ocean acidification: A litmus test for international
law. Carbon & Climate Law Review, 3, 459-471.
Barnosky, A. D., Hadly, E. A., Bascompte, J., Berlow, E. L., Brown, J. H., Fortelius, M., Smith,
A. B. (2012). Approaching a state shift in earth's biosphere. Nature, 486 (7401), 52-58.
Belli, B. (2012). This is your ocean on acid. The Environmental Magazine, 23(3), 21-31.
Calderia, K., & Wickett, M. E. (2003). Anthropogenic carbon and ocean PH. Nature, 425, 365.
Checkley, D. M., Dickson, A. G., Takahashi, M., Radich, A. Eisenkolb, N., & Asch, R. (2012).
Elevated CO2 enhances otolith growth in young fish. Science, 324(5835), 1683.
Denman, K., Christian, J. R., Steiner, N., Portner, H., & Nojiri, Y. (2011). Potential impacts of
future ocean acidification on marine ecosystems and fisheries: Current knowledge and
recommendations for future research. ICES School of Marine Science, 68(6), 1019-1029.
Gruber, N., Hauri, C., Zouhair, L., Loher, D., Frolicher, T. L., & Plattner, G. (2012). Rapid
progression of ocean acidification in the California Current System. Science, 337(6091),
220-223.
Karl, T. R., & Trenberth, K. E. (2003). Modern global climate change. Science, 308(5651),
1431-1434.
Logan, C. A. (2010). A review of ocean acidification and America’s response. BioScience,
60(10), 819-828.
Michael J. McPhaden, Stephen E. Zebiak, and Michael H. Glantz (2006). ENSO as an
Integrating Concept in Earth Science. Science 314 (5806), 1740-1745.
Matthews, H. D., & Cao, L., Calderia. (2009). Sensitivity of ocean acidification to geoengineered
climate stabilization. Geophysical Research Letters, 36, 1-5.
Munday, P. L., Dixon, D. L., Donelson, J. M., Jones, G. P., Pratchett, M. S., Devitsina, G. V., &
Doving, K. B. (2009). Ocean acidification impairs olfactory discrimination and homing
ability of a marine fish. Proceedings of the National Academy of Sciences of the United
States of America, 106(6), 1848-1852.
13
Munday, P. L., Dixson, D. L., McCormick, M. I., Meekan, M., Ferrari, M. C. O., & Chivers, D.
P. (2010). Replenishment of fish populations is threated by ocean acidification.
Proceedings of the National Academy of Sciences of the United States of America,
107(29), 12930-12934.
Orr, J. C., Fabry Victoria J., Aumont, O., Bopp, L., Doney, S. C., Feely, R. A., Yool, A. (2005).
Anthropogenic ocean acidification over the twenty-first century and its impact on
calcifying organisms. Nature, 437(7059), 681-686.
Perry, I. R., Cury, P., Brander, K., Jennings, S., Mollmann, C., & Planque, B. (2010). Sensitivity
of marine systems to climate and fishing: Concepts, issues and management responses.
Journal of Marine Systems, 79(3-4), 427-435.
Quesne, W., & Pinnegar, J. K. (2012). The potential impacts of ocean acidification: Scaling from
physiology to fishes. Fish and Fisheries, 13(3), 333-344.
Raven, J., Caldeira, K., Elderfield, H., Hoegh-Guldberg, O., Liss, P., Riebesell, U., & Watson, A.
(2005). Ocean acidification due to increasing atmospheric carbon dioxide.
Service, R. F. (2012). Rising acidity brings an ocean of trouble. Science, 337(6091), 148-148.
Wittig, T. (2012). Climate change and seafood supply: Developing countries most vulnerable to
ocean acidification. ThinkProgress.
Zeebe, R. E. (2012). History of seawater carbonate chemistry, atmospheric CO2, and ocean
acidification. The Annual Review of Earth and Planetary Sciences, 40, 141-165.
14