Download All Climate Change is Local: Understanding and Predicting the

All Climate Change is Local: Understanding and Predicting the
Effects of Climate Change from an Organism’s Point of View
Brian Helmuth,I Lauren Yamane,II Katharine J. Mach,III
Shilpi Chhotray,IV Phil Levin,V & Sarah WoodinVI
Abstract
Global climate change is exerting profound effects on organisms and ecosystems. As resource
managers and policymakers must contend with the ongoing and future effects of global climate
change, they challenge scientists to predict where, when, and with what magnitude these effects
are most likely to occur. By understanding the processes by which human-managed and natural
ecosystems respond to a changing climate, and by quantifying levels of confidence in our ability
to predict these effects, we may be able to prepare for some of these impacts, a form of
adaptation to climate change.
Here, we describe how knowledge of physiology can help to inform management
decisions. Because physiological tolerance to environmental factors varies between species,
there will likely be “winners” and “losers” in the face of climate change. We explore how a
failure to consider the details of an organism’s physiology and ecology can hamper efforts to
respond proactively to climate change and, conversely, how an understanding of how nonhuman
organisms interact with their environment can help to provide a framework for anticipating and
preparing for future changes in natural and managed ecosystems. We examine some of the
physiological responses of marine organisms to climate change in three examples: thermal stress
in marine invertebrates, ramifications of water temperature changes on fish bioenergetics and
thus on fish reproduction and growth, and effects of changes in wave forces on damage to corals
and kelp. Because factors such as temperature interact with other stressors like overexploitation
and pollution to drive patterns of mortality, it may be possible to prevent some damage by
reducing the impact of stressors not related to climate change. Methods such as ecological
forecasting and the utilization of bioenergetic budgets can be used to help guide future adaptation
to climate change by providing forecasts within a probabilistic framework.
I
University of South Carolina, Department of Biological Sciences, Columbia, SC 29208.
University of South Carolina, Department of Biological Sciences.
III
Stanford University, Hopkins Marine Station, Pacific Grove, CA 93950.
IV
University of South Carolina, Department of Biological Sciences.
V
NOAA Northwest Fisheries Science Center, Seattle, WA 98112.
VI
University of South Carolina, Department of Biological Sciences.
II
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I. INTRODUCTION .................................................................................................................19
II. FUNDAMENTALS OF PHYSIOLOGICAL ECOLOGY RELATED TO CLIMATE
CHANGE .................................................................................................................................20
III. EFFECTS OF WEATHER AND CLIMATE ON ANIMAL BODY TEMPERATURE:
BETWEEN A ROCK AND HOT PLACE ................................................................................23
IV. IMPLICATIONS OF CLIMATE CHANGE FOR FISH AND FISHERIES ........................26
V. LIFE IN STORMIER SEAS: PREDICTING THE EFFECTS OF INCREASING OCEAN
WAVE HEIGHT.......................................................................................................................28
VI. GAZING INTO THE CRYSTAL BALL: PREDICTING THE FUTURE EFFECTS OF
CLIMATE CHANGE ...............................................................................................................32
VI. CONCLUSIONS ................................................................................................................33
I. INTRODUCTION
Global climate change is pervasive in its effects on organisms and ecosystems.1
Although climate change is a worldwide phenomenon, its effects on organisms manifest at very
local levels, and ultimately result from the interactions of individual animals and plants with the
environment in their immediate vicinity.2 As a result, while aspects of the physical environment
(e.g., air and water temperature, salinity, wave height, rainfall, and pH) are all changing as a
result of anthropogenic greenhouse gas emissions,3 the magnitudes of these changes can vary
considerably from location to location. Moreover, because physiological tolerance to these
factors varies among organisms, their impacts will vary considerably among species.4 As a
result, there will likely be “winners” and “losers” as the Earth’s climate continues to be altered.
Reducing greenhouse gas emissions as a means of mitigating global warming is a top
priority. However, we are in many ways already committed to environmental change in the
coming decades.5 Uncertainty in future global output of greenhouse gases remains high,6 but
estimates suggest that even if today’s level of greenhouse gases held steady, the planet’s
temperature would still increase by 0.6°C by 2100.7 A key challenge before the scientific
community is thus to determine the likely magnitudes, locations, and timing of changes in the
physical environment, and then to translate these changes into resulting impacts on natural and
human managed-ecosystems.
1
Terry L. Root et al., Fingerprints of Global Warming on Wild Animals and Plants, 421 N ATURE 57, 57-59 (2003).
Brian Helmuth, From Cells to Coastlines: How Can We Use Physiology to Forecast the Impacts of Climate
Change?, 212 J. EXPERIMENTAL BIOLOGY 753, 754 (2009).
3
Intergovernmental Panel on Climate Change, Summary for Policymakers, in CLIMATE CHANGE 2007: THE
PHYSICAL SCIENCE BASIS. CONTRIBUTION OF WORKING G ROUP I TO THE FOURTH ASSESSMENT REPORT OF THE
INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 5, 5-17 (Susan Solomon et al. eds., 2007) [hereinafter CLIMATE
CHANGE 2007: THE PHYSICAL SCIENCE BASIS].
4
Laura E. Petes et al., Effects of Environmental Stress on Intertidal Mussels and Their Sea Star Predators, 156
OECOLOGIA 671, 677 (2008).
5
CLIMATE CHANGE 2007: SYNTHESIS REPORT. CONTRIBUTION OF WORKING GROUPS I, II AND III TO THE FOURTH
ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 44-45 (Rajendra K. Pachauri &
Andy Reisinger eds., 2007).
6
Id.
7
Gerald A. Meehl et al., Global Climate Projections, in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS,
supra note 3, at 10-17.
2
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In this paper, we discuss some of the mechanisms by which weather and oceanic
conditions affect marine organisms. We explain how understanding the physiology and ecology
of organisms is necessary to make effective and appropriate management and policy decisions.
Furthermore, we argue that through an understanding of physiological responses to climate
change coupled with detailed predictions of how the physical environment is likely to change, it
may be possible to move away from generic predictions of ecological responses (e.g., “poleward
shifts” and “decreases in biodiversity”) and toward a quantitative framework where likely
locations and timings of responses in natural and human-managed ecosystems can be predicted.
In doing so, we can potentially respond to and plan for (i.e., adapt to) some of the inevitable
changes brought about by global climate change. Here we focus on marine ecosystems, but the
principles that we describe are generally applicable to terrestrial and freshwater ecosystems as
well.
We begin the discussion with a review of general principles central to the field of
physiological ecology and the importance of these principles to managing marine ecosystems.
We then explore how factors associated with climate change determine organism responses
within the context of three heuristic examples: (1) mechanisms by which weather drives the body
temperatures of coastal invertebrates and the subsequent impacts of temperature on reproduction
and survival; (2) the linkages of water temperature to the bioenergetics of fish and the
consequences for reproduction, growth, and survival of these fish, and by extension, fisheries;
and (3) probable changes in rates of growth and survival versus damage and mortality given
increases in wave height (and wave-imposed forces) in coastal shallow-water environments.
Within these examples, we discuss physiology-based approaches that marine resource managers
can utilize when factoring climate change into their management decisions. Namely, we explore
the use of bioenergetic budgets for fisheries stock assessments and predictive techniques like
mechanistic ecological forecasting that are based on knowledge of the physiological performance
curves for organisms.
II. FUNDAMENTALS OF PHYSIOLOGICAL ECOLOGY
RELATED TO CLIMATE CHANGE
Physiological ecologists use performance curves8 to define the complex relationships
between organism responses such as growth, reproduction, and survival, and environmental
factors such as temperature. Performance curves describe both the conditions under which an
organism can function and its physiological limits. These curves are almost always nonlinear
and often indicate maximal performance near the upper limit; thus, small changes in factors like
body temperature can lead to large differences in performance, which, in turn, can have
significant impacts on survival and reproduction. Population-level responses of different species
then have cascading influences on ecosystems. Importantly, performance curves are species
specific and can change over the course of an organism’s lifetime as a function of size, age,
exposure to stress, and acclimation.9 When performance curves vary among members of a
population as a result of variable genotypes, families of these curves show the potential for
evolutionary response as a result of selection. Recent research has emphasized some capacity for
8
9
See infra, fig.1.
MICHAEL J. ANGILLETA, THERMAL ADAPTATION: A THEORETICAL AND EMPIRICAL SYNTHESIS 38 (2009).
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rapid evolutionary responses to climate change within some populations, although the extent to
which evolution can prevent localized extinctions remains unclear.10
Importantly, there are likely to be “winners” and “losers” in organismal responses to
climate change, depending on how close organisms are living to their environmental limits and
their thermal optima. Which species or populations are “winners” or “losers” may be determined
by comparing the performance curves of a range of species under different climate scenarios.
Invasive species appear to be one group of “winners.” Many invasive plants and animals are able
to tolerate wide-ranging environmental conditions11 and can have large, negative impacts on
native ecosystems once established. In general, species vary significantly in their sensitivity to
factors such as body temperature and carbon dioxide.12 As a result, the responses of organisms
to climate change will likely vary widely. While overall effects on ecosystems are expected to
be negative, it is important to identify positive, negative, and neutral effects on organisms on a
species-by-species basis. Not only will such an approach permit the generation of sophisticated,
quantitative predictions of the ecological impacts of climate change, but also it may (especially
in the case of commercially and ecologically important species) permit effective planning for
future climate change scenarios.
Changes in global climate are likely to be spatially and temporally heterogeneous, as will
subsequent damage to organisms and ecosystems.13 It thus may be possible to identify locations
where impacts will be comparatively minimal (“refugia”), at least in the short-term (i.e., twenty
to fifty years), and, conversely, where changes will be most dramatic over the same time period.
Identification of temporally persistent refugia will be important for the emplacement of protected
areas and the maintenance of stocks of commercially important species.14 Effective planning
therefore should include, whenever possible, an understanding of temporal and spatial patterns of
environmental stressors (e.g., temperature, waves, pH), as well as responses of organisms and
communities to those stressors. For example, Hoffman cautions that the emplacement of marine
reserves should be at locations where ecosystems not only function well now, but also will
function well in the future. Because patterns of abundance, stress, and mortality can be
complicated,15 such strategies are similarly complex in their undertaking.
Changes in abundance and shifts in species ranges occur not only as the result of “acute”
extremes, which kill organisms over periods of days and weeks, but also as the result of slower,
more chronic, cumulative stressors (longer duration, but typically of smaller magnitude) that
10
See C. Parmesan, Ecological and Evolutionary Responses to Recent Climate Change, 37 ANN. REV. ECOLOGY
EVOLUTION & SYSTEMATICS 637, 656 (2006).
11
Peter A. Fields, Emily L. Rudomin & George N. Somero, Temperature Sensitivities of Cytosolic Malate
Dehydrogenases from Native and Invasive Species of Marine Mussels (Genus Mytilus): Sequence-Function
Linkages and Correlations with Biogeographic Distribution, 209 J. EXPERIMENTAL BIOLOGY 656, 656-57 (2006).
12 U.S. CLIMATE CHANGE S CI. P ROGRAM & THE SUBCOMM. ON GLOBAL CHANGE RES., U.S. ENVTL. P ROTECTION
AGENCY, THE EFFECTS OF CLIMATE CHANGE ON AGRICULTURE, LAND RESOURCES, WATER RESOURCES, AND
BIODIVERSITY 27, 50-51, 60-62, 70-71 (2008).
13
Brian S. Helmuth et al., Climate Change and Latitudinal Patterns of Intertidal Thermal Stress, 298 SCIENCE 1015,
1015 (2002).
14
Jennifer Hoffman, Temperate Marine, in BUYING TIME: A USER'S MANUAL FOR BUILDING RESISTANCE AND
RESILIENCE TO CLIMATE CHANGE IN NATURAL SYSTEMS 123, 140 (Lara J. Hansen et al. eds., 2003).
15
Helmuth et al., supra note 13, at 1015-17; Sean P Place, Michael J. O’Donnell & Gretchen E. Hofmann, Gene
Expression in the Intertidal Mussel Mytilus californianus: Physiological Response to Environmental Factors on a
Biogeographic Scale, 356 MARINE ECOLOGY PROGRESS SERIES 1, 1 (2008); Raphael D. Sagarin & George N.
Somero, Complex Patterns of Expression of Heat-Shock Protein 70 Across the Southern Biogeographical Ranges of
the Intertidal Mussel Mytilus californianus and Snail Nucella ostrina, 33 J. BIOGEOGRAPHY 622, 622-23 (2006).
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reduce growth, health, and reproduction.16 For example, Harley and Paine showed that mortality
in intertidal algae can be driven by rare, unpredictable events.17 In contrast, data also exist for
strong sublethal tissue losses in intertidal algae.18 Similarly, Beukema et al. showed that the
bivalve Macoma balthica, a species with a low tolerance for high temperatures, experienced
temperatures well within its range boundaries that increased mortality and reduced growth,
suggesting that sublethal effects can be an important response to changing environmental
conditions;19 and Hummel et al. showed that the distribution of M. balthica was determined not
by a single environmental factor but rather by chronic, interactive stressors that affected
metabolism and capacity for growth.20
Similarly, while extremes in body temperature are deadly, it is often not the maximum
temperature per se that drives mortality, but rather the difference between extremes of
temperatures to which animals are acclimated.21 For example, one widely used means of
estimating large-scale patterns of coral bleaching and mortality has been the estimation of
Degree Heating Weeks (DHW), a measurement of the amount of time that a coral spends above
the “normal” local temperature maximum.22 In other words, the time history of exposure can
make a large difference to survival. Studies with other species such as intertidal crabs have
borne out this pattern, and while they suggest that some organisms may be able to acclimate
temporarily to changes in temperature, any significant increase beyond the normal range can be
deadly.23 Therefore, both long term sublethal (“chronic”) stressors and extreme, short duration
stressors (“acute”) contribute to ecological responses to climate change. 24 Changes in natural
ecosystems may thus be difficult to detect in the absence of long-term monitoring of population
sizes, reproduction, and growth, suggesting that understanding the physiological mechanisms
that drive changes is crucial to identifying and predicting marine ecosystem responses to climate
change.25
Some stressors and their impacts on organisms and ecosystems are predictable, at least
over the scale of decades; others are more stochastic in nature or are so complex in their effects
that they are unlikely to be predictable to any practical degree except in generalities. For
example, Crain et al. reviewed interactions among multiple environmental stressors and found
16
George N. Somero, Thermal Physiology and Vertical Zonation of Intertidal Animals: Optima, Limits, and Costs of
Living, 42 INTEGRATED & COMP. BIOLOGY 780, 780 (2002).
17
Christopher D. G Harley & Robert T. Paine, Contingencies and Compounded Rare Perturbations Dictate Sudden
Distributional Shifts During Periods of Gradual Climate Change, 106 PNAS 11172, 11174 (2009).
18 Wayne P. Sousa, Disturbance in Marine Intertidal Boulder Fields: The Nonequilibrium Maintenance of Species
Diversity, 60 ECOLOGY 1231-32 (1979).
19
Jan J. Beukema et al., Some Like It Cold: Populations of the Tellinid Bivalve Macoma balthica (L.) Suffer in
Various Ways from a Warming Climate, 384 MARINE ECOLOGY PROGRESS SERIES 135, 135, 143 (2009).
20
Herman Hummel et al., The Respiratory Performance and Survival of the Bivalve Macoma balthica ( L.) at the
Southern Limit of its Distribution Area: A Translocation Experiment, 251 J. EXPERIMENTAL MARINE BIOLOGY &
ECOLOGY 85, 97-100 (2000).
21
Karl D. Castillo & Brian S. T. Helmuth, Influence of Thermal History on Response of Montastraea annularis to
Short-Term Temperature Exposure, 148 MARINE BIOLOGY 261, 266-69 (2005).
24
Michael W. Gleeson & Alan E. Strong, Applying MCSST to Coral Reef Bleaching, 16 ADVANCES SPACE RES.
151, 151, 153 (1995).
23
See, e.g., Jonathon H. Stillman, Acclimation Capacity Underlies Susceptibility to Climate Change, 301 SCIENCE
65, 65 (2003).
24
Brian S. T. Helmuth & Gretchen E. Hofmann, Microhabitats, Thermal Heterogeneity, and Patterns of
Physiological Stress in the Rocky Intertidal Zone, 201 BIOLOGICAL BULL. 374, 374, 382 (2001).
25
Brian Helmuth et al., Living on the Edge of Two Changing Worlds: Forecasting the Response of Rocky Intertidal
Ecosystems to Climate Change, 37 ANN. REV. ECOLOGY EVOLUTION & SYSTEMATICS 373, 382, 393-94 (2006).
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that approximately twenty-five percent of the interactions surveyed showed additive
(cumulative) effects, thirty-six percent of the interactions showed synergistic (enhanced) effects,
and thirty-eight percent were antagonistic (diminished).26 In other words, in some cases, effects
could be predicted based on the actions of individual stressors, but in the majority of cases, the
interactive effects of multiple stressors were either less or more than expected.
To some extent, the interactions of organisms with their environments are predictable,
based on an extensive and growing literature of physiological performance curves. Techniques
like Ecological Forecasting—a means by which physiological performance is compared against
predicted environmental conditions—may assist in assessing future ecological responses to
climate change27 and can aid in spatial environmental management planning,28 but only if the
forecasts have a mechanistic basis and quantitatively describe the complex interactions among
the physical environment, physiological responses of organisms, and the subsequent emergent
impacts on ecological communities. Moreover, given the complexities and uncertainties inherent
in making such predictions, it is important to quantitatively estimate levels of uncertainty.
Physiology, then, is clearly central to understanding past and current responses and to
predicting future responses of organisms to global climate change; however, effective planning
will likely require that we move beyond examinations of single stressors, and instead explore the
sum of interacting and potentially conflicting stressors related to climate change. In the three
scenarios below, we attempt to expand on this theme, illustrating the interacting environmental
forces on organisms and how they can be approached. The first two scenarios focus on
physiological responses primarily to temperature as a proxy for effects of global climate change,
discussing changes in growth, reproduction and survival. The third scenario focuses on the
physiological stresses imposed by increasing wave height due to global climate change, with
resulting changes in growth, reproduction and survival. The common thread is the physiological
mechanisms and impacts on the currencies of fitness: growth, reproduction and survival.
III. EFFECTS OF WEATHER AND CLIMATE ON ANIMAL BODY
TEMPERATURE: BETWEEN A ROCK AND HOT PLACE
The temperature of an animal or plant’s body affects virtually all of its physiological
processes and, as such, is often a critical environmental stressor. Physiological stress is here
defined as any response by an organism that reduces its ability to survive, grow, or reproduce.29
With climate change will come both more acute and chronic expression of temperature stress.
Enzyme function, production of proteins, and rates of metabolism are all affected by body
temperature, and under extreme conditions, many of these processes shut down or otherwise
compromise cellular function.30 More subtle but nonetheless important effects include the
26
Caitlin M. Crain, Kristy K. Kroeker & Benjamin S. Halpern, Interactive and Cumulative Effects of Multiple
Human Stressors in Marine Systems, 11 ECOLOGY LETTERS 1304, 1304-06 (2008).
27
James S. Clark et al., Ecological Forecasts: An Emerging Imperative, 293 SCIENCE 657, 657-59 (2001).
28
Hoffman, supra note 14, at 140; Ove Hoegh-Guldberg et al., Assisted Colonization and Rapid Climate Change,
321 SCIENCE 345, 345 (2008).
29
John C. Wingfield & Alexander S. Kitaysky, Endocrine Responses to Unpredictable Environmental Events:
Stress or Antistress Hormones? 42 INTEGRATED & COMP. BIOLOGY 600, 601 (2002).
30
PETER W. HOCHACHKA & G EORGE N. SOMERO, BIOCHEMICAL ADAPTATION: MECHANISM AND PROCESS IN
PHYSIOLOGICAL EVOLUTION 290-96 (2002).
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impacts of both short-term and longer-term changes in temperature on feeding rates, growth,31
locomotion,32 and reproductive output.33 Temperature is thus an overarching environmental
factor driving the survival, reproduction, and overall physiological health of life on Earth.
Recent evidence has shown that, largely as a result of extremes in temperature, increasing stress
on animals and plants has led to shifts in species ranges, the timing of events like flowering and
reproduction, and the localized extinction of organisms like corals.34 Measuring and modeling
current and future patterns of body temperature in animals is therefore likely to provide
significant insight into how climate currently sets organismal range boundaries, and thus, how
climate change will likely result in future range shifts.
To any organism, the only temperature that matters to its physiological performance is
that of its body, as opposed to that of the surrounding air, water or sea surface. Endothermic
animals, including mammals, maintain a relatively constant body temperature, but in cold
environments, the maintenance of a temperature above that of ambient comes at a significant
metabolic cost. Conversely, in hot environments, remaining in the shade can lead to reductions
in foraging time. In contrast, the body temperature of most marine invertebrates and algae
changes with the temperature of the surrounding environment. Indeed, in some cases, measuring
a marine organism’s body temperature patterns is fairly straightforward, as the temperature of
aquatic animals is often similar to that of the surrounding water.35 Recent reports suggest that as
many as eighty percent of the corals in some Caribbean locations may have been lost due to
slight increases in water temperature, which pushed corals and the symbiotic algae living within
their tissues above their physiological limits.36 For shallow water subtidal organisms, sea surface
temperature (SST) can potentially serve as an effective proxy for organism body temperature;
however, for organisms deeper than a few meters, water temperatures (and body temperatures)
are often substantially different from that of SST, making predictions of body temperature
patterns difficult.37
For organisms of the intertidal region (the portion of the shore exposed between high and
low tide), the proximal cause of organism responses to climate change are even more difficult to
untangle. As is the case for terrestrial invertebrates, body temperatures of animals during low
tide are driven by the complex interaction of air and ground temperature, wind speed, humidity,
and solar radiation. Just as asphalt heated by the sun reaches temperatures well above that of the
surrounding air, intertidal organisms experience body temperatures that are very different than
the surrounding air, due to the interacting effects of convective, radiative, conductive, and long
31
Eric Sanford, The Feeding, Growth, and Energetics of Two Rocky Intertidal Predators (Pisaster ochraceus and
Nucella canaliculata) Under Water Temperatures Simulating Episodic Upwelling, 273 J. EXPERIMENTAL MARINE
BIOLOGY & ECOLOGY 199, 199 (2002).
32
Mark D. Bertness & David E. Schneider, Temperature Relations of Puget Sound Thaids in Reference to Their
Intertidal Distribution, 19 V ELIGER 47, 49-50 (1976).
33
Brian L. Bayne, Reproduction in Bivalve Molluscs Under Environmental Stress, in PHYSIOLOGICAL ECOLOGY OF
ESTUARINE ORGANISMS 264 (F. John Vernberg ed., 1975).
34
Parmesan, supra note 10.
35
But see Katherina E. Fabricius, Effects of Irradiance, Flow, and Colony Pigmentation on the Temperature
Microenvironment Around Corals: Implications for Coral Bleaching? 51 LIMNOLOGY & OCEANOGRAPHY 30, 30
(2006) (stating that “the warming of colony surfaces increased with increasing colony pigmentation”).
36
Simon D. Donner, Thomas R. Knutson & Michael Oppenheimer, Model-Based Assessment of the Role of HumanInduced Climate Change in the 2005 Caribbean Coral Bleaching Event, 104 PNAS 5483, 5483, 5486-87 (2007).
37
James J. Leichter, Brian Helmuth & Andrew M. Fischer, Variation Beneath the Surface: Quantifying Complex
Thermal Environments on Coral Reefs in the Caribbean, Bahamas and Florida, 64 J. MARINE RES. 563, 563-64,
583-84 (2006); Fabricius, supra note 35, at 35.
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wave (infrared) heat exchange.38 As a result, air temperature can, in some cases, be a poor proxy
for the physiological effects of weather and climate on animals exposed to the air at low tide.39
For some intertidal organisms, daily ranges of body temperature can exceed twenty-five degrees
Celsius (forty-five degrees Fahrenheit).40 Consequently, given our very anthropocentric view of
weather, the effects of changes in weather on nonhuman organisms are often difficult to
comprehend and require an understanding both of physiology and of how weather and climate
determine an organism’s body temperature. As a result, geographic patterns in body temperature
in intertidal organisms can be complex; for example, intertidal animals are not necessarily
warmer at lower latitudes.41 Comparably, patterns of physiological stress42 and species
abundance43 also show complex patterns along geographic gradients.
Complex spatial patterns in physiological stress and species abundance are often the
result of smaller, more chronic changes in temperature that negatively impact energy available
for growth, reproduction, or basic metabolic functions, or are the result of several interacting
factors, of which temperature is only one variable.44 Some of these variables are known to be
changing rapidly and are usually grouped under the rubric of “climate change;”45 however, many
other factors not directly related to global climate change, such as changes in habitat availability,
overexploitation and pollution, can be equally important to organism health and survival.
Specifically, while factors related to climate change (e.g., impacts on the temperature of
organisms) can kill or harm organisms directly,46 these factors often interact with one another47
and with other stressors, such as fishing pressure, competition, food availability, pollution,
development and nutrient levels, to drive patterns of mortality and stress.48 Thus, climate change
is often the “trigger that fires the bullet” in that it produces additional stress on organisms already
exposed to other harmful factors (or vice versa). 49 For example, temperature, salinity and heavy
38
Warren P. Porter & David M. Gates, Thermodynamic Equilibria of Animals with Environment, 39 ECOLOGICAL
MONOGRAPHS 227, 227 (1969).
39
Helmuth et al., supra note 25, at 383.
40
David W. Elvin & Jefferson J. Gonor, The Thermal Regime of an Intertidal Mytilus californianus Conrad
Population on the Central Oregon Coast, 39 J. EXPERIMENTAL MARINE BIOLOGY & ECOLOGY 265, 265, 268 tbl.2
(1979) (describing mussel tissue temperatures at various time points); see also Brian Helmuth, How Do We Measure
the Environment? Linking Intertidal Thermal Physiology and Ecology Through Biophysics, 42 INTEGRATED &
COMP. BIOLOGY 837, 840 figs.A-C (2002).
41
Helmuth et al., supra note 25, at 385, 394.
42
Place et al., supra note 15, at 1, 13.
43
Sagarin & Somero, supra note 15, at 622.
44
Theodore R. Rice & Randolph L. Ferguson, Response of Estuarine Phytoplankton to Environmental Conditions,
in PHYSIOLOGICAL ECOLOGY O F ESTUARINE ORGANISMS, supra note 33, at 1, 3 tbl.1.
45
See Alan J. Southward et al., Long-Term Oceanographic and Ecological Research in the Western English
Channel, 47 ADVANCES IN MARINE BIOLOGY 13, 13-54 (2005) (examining the impact of climatic changes on coastal
ecosystems, including effects on biological factors like water temperature and salinity, currents and circulation,
nutrients, and productivity).
46
See Hochachka & Somero, supra note 30, at 290-96.
47
Hans O. Pörtner, Martina Langenbuch & Basile Michaelidis, Synergistic Effects of Temperature Extremes,
Hypoxia, and Increases in CO2 on Marine Animals: From Earth History to Global Change, 110 J. OF GEOPHYSICAL
RES. 1, 1 (2005).
48
Denise L. Breitburg & Gerhardt F. Riedel, Multiple Stressors in Marine Systems, in MARINE CONSERVATION
BIOLOGY: THE SCIENCE OF MAINTAINING THE SEA’S BIODIVERSITY 167, 167-77 (Elliott Norse & Larry Crowder
eds., 2005).
49
Crain et al., supra note 26, at 1311.
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metal pollution all interact to drive stress in marine invertebrates.50 Similarly, desiccation, waveinduced forces and herbivory interact to drive defoliation in marine algae.51 As a result, while it
may not always be possible to locally ameliorate environmental factors such as temperature,
organisms can nevertheless be prevented from exceeding physiological thresholds through the
mitigation of other factors like fishing pressure, pollution, and development.52
IV. IMPLICATIONS OF CLIMATE CHANGE FOR FISH AND FISHERIES
The energy budget of an organism is a quantitative description of where each unit of
energy consumed goes. For example, all energy consumed by a fish fuels its metabolism, is lost
as waste, is lost to predation, or is incorporated into the fish as new tissue, resulting in
organismal growth or reproduction. Understanding the energy budget of an animal allows
researchers to determine how food intake affects the functioning of the whole organism.
Bioenergetic budgets have been particularly useful for producing estimates of growth, feeding
rates and reproductive output.53 Importantly, rates of biochemical reactions are strongly
influenced by temperature. Since the body temperature of most fishes is a function of their
environment,54 all aspects of fish biology are directly affected by changes in water temperature.
Specifically, consumption rates, total metabolic rates, swimming ability (and thus both prey
capture and predation avoidance), and the rate of waste loss are all critically dependent on
temperature.55 The potential effects of climate change on fish bioenergetics were wonderfully
illustrated by Harvey, who used a bioenergetics model to estimate that during El Niño events
(and possibly other climate events), female blue rockfish (Sebastes mystinus), an important,
recreationally fished species in California, experience lower growth rates and reduced fecundity,
implying a decline in the amount of food consumed.56 This reduction in consumption appears to
be due to a reduction in food supply for the fish due to changes in circulation during El Niño
events and thus is likely to be true of other fish as well. Over the lifespan of fish, repeated
exposure to El Niño conditions resulted in significant delays in the age of maturation.57 This
occurred because El Niño conditions reduced the amount of energy available for growth and the
development of reproductive tissue. Since blue rockfish spawn every year, delayed maturation
in combination with reduced fecundity during El Niño events means that over the lifetime of a
blue rockfish, there is a massive reduction in lifetime egg production.58 This effect was even
more drastic as fishing pressure increased.59
50
Charles L. McKenney & Jerry M. Neff, Individual Effects and Interactions of Salinity, Temperature, and Zinc on
Larval Development of the Grass Shrimp Palaemonetes pugio. I. Survival and Developmental Duration Through
Metamorphosis, 52 MARINE BIOLOGY 177, 177 (1979).
51
See Sousa, supra note 18.
52
Jeremy B. C. Jackson, Ecological Extinction and Evolution in the Brave New Ocean, 105 PNAS 11458, 11464
(2008).
53
S. Marshall Adams & James E. Breck, Bioenergetics, in METHODS FOR FISH BIOLOGY 389, 309-91 (Carl B.
Schreck & Peter B. Moyle eds., 1990).
54
PETER B. MOYLE & JOSEPH J. CECH, FISHES: AN INTRODUCTION TO ICHTHYOLOGY 36-38 (1988).
55
Hochachka & Somero, supra note 30, at 404-05.
56
Chris J. Harvey, Effects of El Niño Events on Energy Demand and Egg Production of Rockfish (Scorpaenidae:
Sebastes): A Bioenergetics Approach, 103 FISHERY BULL. 71, 71-83 (2005).
57
Id. at 75-76.
58
Id.
59
Id. at 79.
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Bioenergetics approaches assume fish cannot alter their environment, but many species of
fish have the ability to behaviorally regulate their body temperature by changing depths or
latitudes.60 For example, a model of the distribution of the yellow croaker (Larimichthys
polyactis) in the East China Sea predicted that an increase in ocean temperature would create
physiological demands that would force a northward shift in the population.61 As a result, the
potential fisheries harvest near the southern portion of this species range would drop, while catch
would increase in the northern portion of the yellow croaker’s range.
A key challenge for understanding the potential influence of climate change on fish
stocks is to move beyond a single species to consider how entire assemblages of species might
respond to temperature changes. Because of differences in life history and behavior, not all
species of fish will respond in the same way to changes in temperature.62 Moreover, different
species of fish have very different histories of exploitation, resulting in differences in the size
structure of populations.63 Managing entire assemblages of fishes requires anticipating which
species are most sensitive to environmental variability, understanding how they will compensate
physiologically or behaviorally, and incorporating this information into fisheries stock
assessments.64
By considering the sensitivity of bioenergetics models developed for different species to
changing temperature, we can make predictions about which species are likely to respond most
strongly to climate change. For instance, age of maturity in rockfishes and sharks appears to be
far more responsive to temperature changes than it is in other fish like sablefish.65 Consumption
also correlates positively with temperature, with rockfishes relatively more responsive than either
sharks or sablefish.66 Interestingly, however, because sablefish are highly abundant, modest
change in sablefish consumption rates as a function of temperature will have a greater impact on
prey than will changes in consumption rates by either spiny dogfish or rockfish, which are less
abundant but show a greater temperature feeding response.67
Vulnerability to fishing is influenced by a number of life history parameters, including
size, age at maturity, fecundity, lifespan, growth rate, natural mortality rates, geographic range,
and spatial behavior.68 As previously highlighted, different species will exhibit different
responses to temperature changes, but unfortunately, a careful study of “winners” and “losers” of
ocean climate change has not yet been undertaken. One reason is that, although some responses
are simple bioenergetic outcomes, other responses are more complex. For instance, the age of
maturity has clear implications for fisheries management; since it is related to generation time,
maximum size and long-term reproductive output, it underlies the ability of a fish stock to
rebound from over-fishing. A complication exists, however, in the trade-off between age of
60
Sanford, supra note 31, at 210.
William Cheung et al., Application of Macroecological Theory to Predict Effects of Climate Change on Global
Fisheries Potential, 365 MARINE ECOLOGY PROGRESS SERIES 187, 192 (2008).
62
Steven A. Murawski, Climate Change and Marine Fish Distributions: Forecasting from Historical Analogy, 122
TRANSACTIONS A M. FISHERIES SOC’Y 647, 653 fig.5 (1993).
63
Phillip S. Levin et al., Shifts in a Pacific Ocean Fish Assemblage: The Potential Influence of Exploitation, 20
CONSERVATION BIOLOGY 1181, 1185 (2006).
64
Jackie R. King & G.A. Mcfarlane, A Framework for Incorporating Climate Regime Shifts into the Management of
Marine Resources, 13 FISHERIES MGMT. & ECOLOGY 93, 93-96 (2006).
51
Chris J. Harvey, Effects of Temperature Change on Demersal Fishes in the California Current: A Bioenergetics
Approach, 66 CAN. J. FISHERIES & AQUATIC SCI. 1449, 1456 (2009).
66
Id. at 1449, 1454-55, 1457.
67
Id.
68
See, e.g., Levin et al., supra note 63, at 1186.
61
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ALL CLIMATE CHANGE IS LOCAL
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maturity and maximum size. This trade-off occurs because rapid juvenile growth results in
earlier maturation, but upon reaching maturity, fish allocate much of their subsequent energy
intake to reproduction, thereby reducing maximum size.69 Consequently, in addition to changes
in the number of fish available for fisheries, warming temperatures will change the sizes of
available adults, thus, changing reproductive output per individual female.
Given that climate change will likely influence the basic physiology of fish, often in
predictable ways, how should fisheries managers respond? We focus here on single-species
fisheries management because, as much as ecosystem-based approaches have been advocated, 70
U.S. regional fisheries management councils still focus on single-species stock assessments. A
basic approach to deal with climate change can be illustrated with one of the simplest fisheries
stock assessment models: a yield-per-recruit (YPR) model. YPR models assess changes in the
biomass of a cohort by balancing the increase in the biomass of the cohort from growth against
loss in biomass as a result of natural and fishing mortality.71 In essence, the fundamental YPR
model predicts that fisheries yield is a function of the number of fish, their average weight, and
the fishing mortality experienced by the stock. In this framework, as only fishing mortality and
the youngest age fish that is harvested are controlled by fisheries management, YPR is often used
to determine a fishing rate that maximizes the fisheries yield to be obtained per fish recruited into
the fishery.
Because standard fisheries models such as YPR already consider growth rates, and, as
described above, bioenergetic models provide a relatively simple way to estimate how growth
rates will change as a function of temperature, it is straightforward to consider how aspects of
climate change will influence fisheries. Given predicted effects of temperature on growth, stock
assessment scientists can determine fishing modalities that maximize YPR under various climate
scenarios. Hence, even without complex population models, a simple understanding of the
physiological response of fish to temperature can yield straightforward advice about how much
fishing mortality would need to change in order to compensate for changes in growth rate.
Because of the complications outlined above, such advice would be incomplete; nonetheless, it
provides a starting point for considering how fisheries management should adjust to achieve the
goal of providing sustainable fisheries against a backdrop of climate change.
V. LIFE IN STORMIER SEAS: PREDICTING THE EFFECTS
OF INCREASING OCEAN WAVE HEIGHT
Evidence is mounting that ocean wave heights and the intensity of large storms have
already increased72 and will continue to increase.73 Long-term measurements of wave heights
have been combined with analysis of large-scale climate variations to identify storm and wave
69
David Berrigan & Eric L. Charnov, Reaction Norms for Age and Size at Maturity in Response to Temperature: A
Puzzle for Life Historians, 70 OIKOS 474, 475 tbl.1, 476 (1994).
70
See, e.g., KAREN MCLEOD & HEATHER LESLIE, ECOSYSTEM-BASED MANAGEMENT FOR THE OCEANS 3-7 (2009).
71
SIMON JENNINGS, MICHEL J. KAISER & JOHN D. REYNOLDS, MARINE FISHERIES ECOLOGY 145-49 (2001).
72
Cynthia Rosenzweig et al., Assessment of Observed Changes and Responses in Natural and Managed Systems, in
CLIMATE CHANGE 2007: IMPACTS, A DAPTATION AND VULNERABILITY. CONTRIBUTION OF WORKING GROUP II TO
THE FOURTH ASSESSMENT REPORT OF THE INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE 79, 92-93, 109-10
(Martin L. Parry et al. eds., 2007).
73
Gerald A. Meehl et al., Global Climate Projections, in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS,
supra note 3, at 751, 788-89.
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height patterns in many ocean regions, both over the past fifty years74 and into the future. 75
Since 1950, significant wave height (i.e., the average height of the highest third of waves) has
increased along all U.S. coastlines, especially in the North Atlantic and North Pacific.76 Looking
forward to the coming century, the Intergovernmental Panel on Climate Change (IPCC) now
projects that many mid-latitude ocean regions will experience further increases in wave heights
as climate change proceeds. The increase will result from changes in extratropical (mid-latitude)
storms. The IPCC also projects that tropical cyclones (hurricanes and typhoons) will similarly
become more intense, with greater wind speeds.77 Although increasing wave height poses
distinct threats to humans through more extreme coastal flooding and erosion,78 here we focus on
ramifications for natural ecosystems.
Ocean waves drive rapid water movement in shallow nearshore environments, which
extend from the shoreline to the greatest ocean depths for which water motions caused by surface
waves affect the seafloor—often twenty-meter water depth. The hydrodynamic forces associated
with this water motion shape the dynamics of ecosystems. The vertical height of a wave
determines, in large part, the water velocities associated with the wave when it breaks in shallow
waters. Breaking waves then interact with local topography (e.g., horizontal and vertical rocky
surfaces) to determine the local velocities experienced by marine organisms. In general, waves
with greater offshore heights cause larger nearshore water velocities and forces, although this
trend does not always hold (as will be discussed subsequently in this section).79 Water velocities
on deep coral reefs reach one meter per second (m/s) on a daily basis and five m/s during
storms,80 while velocities of five to ten m/s occur commonly on exposed intertidal shores.
Maximum intertidal velocities in excess of thirty-five m/s (approximately eighty miles per hour)
have been measured.81 Because water is much denser than air, water traveling at two m/s and
winds blowing at one hundred thirty miles per hour impose similar forces. In shallow nearshore
ecosystems, many of the dominant organisms like corals and seaweeds have little mobility.
Instead, they are stationary, permanently attached to rock or other substrata such that they are
See, e.g., Jonathan C. Allan & Paul D. Komar, Climate Controls on US West Coast Erosion Processes, 22 J.
COASTAL RES. 511, 512-18, 527 (2006); Nicholas E. Graham & Henry Diaz, Evidence for Intensification of North
Pacific Winter Cyclones Since 1948, 82 BULL. AM. METEOROLOGICAL SOC’ Y 1869, 1869, 1889 (2001); Susan
Solomon et al., Technical Summary, in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS, supra note 3, at 41,
43; Kevin E. Trenberth et al., Observations: Surface and Atmospheric Climate Change, in CLIMATE CHANGE 2007:
THE PHYSICAL SCIENCE BASIS, supra note 3, at 239, 281, 283-85, 304, 308, 312-13, 315-16; David K. Woolf et al.,
Variability and Predictability of the North Atlantic Wave Climate, 107 J. GEOPHYSICAL RES. (OCEANS) 3145, 3145
(2002).
75
Meehl et al., supra note 73, at 751, 783, 788-89.
76
See Trenberth et al., supra note 74, at 285 fig.3.25.
77
Intergovernmental Panel on Climate Change, Summary for Policymakers, in CLIMATE CHANGE 2007: THE
PHYSICAL SCIENCE BASIS, supra note 3, at 15-16; Christensen et al., Regional Climate Projections, in CLIMATE
CHANGE 2007: THE PHYSICAL SCIENCE BASIS, supra note 3, at 864, 887; Meehl et al., supra note 73, at 751, 783,
786-89; S. Solomon et al., Technical Summary, in CLIMATE CHANGE 2007: THE PHYSICAL SCIENCE BASIS, supra
note 3, at 52.
78
Intergovernmental Panel on Climate Change, Summary for Policymakers, in CLIMATE CHANGE 2007: THE
PHYSICAL SCIENCE BASIS, supra note 3, at 12, 14, 18.
79
See Brian Helmuth & Mark W. Denny, Predicting Wave Exposure in the Rocky Intertidal Zone: Do Bigger Waves
Always Lead to Larger Forces?, 48 LIMNOLOGY & OCEANOGRAPHY 1338, 1338-39, 1344 (2003).
80
Joshua S. Madin, Mechanical Limitations of Reef Corals During Hydrodynamic Disturbances, 24 CORAL REEFS
630, 632 (2005).
81
Katharine J. Mach, Mechanical and Biological Consequences of Repetitive Loading: Crack Initiation and Fatigue
Failure in the Red Macroalga Mazzaella, 212 J. EXPERIMENTAL BIOLOGY 961, 961 (2009).
74
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exposed to the brunt of each passing wave. Thus, organisms in nearshore environments may
endure the equivalent of hurricane-wind forces every few seconds as waves crash onto shore
continually throughout the day.
Despite these staggering water motions, ecosystems associated with intertidal rocks, coral
reefs, kelp forests, and other nearshore environments host some of the most dense and diverse
assemblages of organisms on Earth. For human communities around the globe, these
biologically unique ecosystems provide a plethora of ecosystem services, from fisheries and
ecotourism to protection against coastal erosion. 82 Understanding how these ecosystems will
fare in a regime of increased wave heights therefore assumes great importance.
Several biological questions thus arise, the answers to which may help guide
environmental decision-making. First, how will increasing wave heights impact rates of
breakage and dislodgment? Second, which species will continue to grow and persist in
environments with increased wave heights, and which species will perish, unable to endure the
greater wave forces? And ultimately, what will be the ecosystem-level consequences of these
shifts in species assemblages? Coral reef ecosystems provide one set of answers to these
questions.
Coral reefs create habitat for myriad species and support numerous ecosystem services.
Increasing ocean temperatures and acidity perhaps present the most serious threats to coral
persistence in the coming century,83 but increasing wave heights, which have received less
attention in this context, will also change the composition of coral reefs.
When ocean waves are big enough, the resulting wave-induced forces can cause corals to
84
break.
Corals come in different shapes and sizes, ranging from small to large and from
branched to boulder-shaped. The probability of dislodgement is a function of the coral shape
(degree of streamlining), area exposed to flow, and the strength of attachment of the coral to the
reef. Consequently, corals of varying shapes and sizes have different susceptibilities to
breakage. Through extensive studies and modeling,85 Madin et al. have found that, as wave
heights increase with climate change, branching and “table” corals will break more readily than
boulder-shaped, “massive” corals.86 As a result, composition of the reef will shift towards
massive corals, away from the abundant branching and table corals present today. Acting
synergistically, ocean acidification will weaken the attachment of corals to the substratum and
accelerate this transition among corals.87 In turn, the whole reef ecosystem may change:
herbivorous fishes favor branching-coral habitats, and without sufficient grazing by these fishes,
Gretchen Daily et al., Ecosystem Services: Benefits Supplied to Human Societies by Natural Ecosystems, 2 ISSUES
ECOLOGY 2, 2 (1997); Cecilia M. Holmlund & Monica Hammer, Ecosystem Services Generated by Fish
Populations, 29 ECOLOGICAL ECON. 253, 254-60 (1999); Fredrik Moberg & Patrik Rönnbäck, Ecosystem Services of
the Tropical Seascape: Interactions, Substitutions and Restoration, 46 OCEAN & COASTAL MGMT. 27, 31 tbls.1-2
(2003).
83
Intergovernmental Panel on Climate Change, Summary for Policymakers, in CLIMATE CHANGE 2007: THE
PHYSICAL SCIENCE BASIS, supra note 3, at 11-12.
84
Mark W. Denny & Brian Gaylord, Marine Ecomechanics, 2 ANN. REV. MARINE SCI. 1, 3-5 (2009); Madin, supra
note 80, at 630.
85
See, e.g., Madin, supra note 80, at 630-34; Joshua S. Madin & Sean R. Connolly, Ecological Consequences of
Major Hydrodynamic Disturbances on Coral Reefs, 444 N ATURE 477, 477-80 (2006); Joshua S. Madin, Kerry P.
Black & Sean R. Connolly, Scaling Water Motion on Coral Reefs: From Regional to Organismal Scales, 25 CORAL
REEFS 635, 635 (2006).
86
Denny & Gaylord, supra note 84, at 5; Joshua S. Madin, Michael J. O’Donnell & Sean R. Connolly, ClimateMediated Mechanical Changes to Post-Disturbance Coral Assemblages, 4 BIOLOGY LETTERS 490, 490-92 (2008).
87
Madin, O’Donnell & Connolly, supra note 86, at 490, 492.
82
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algae overgrow reefs.88 Reefs consisting of smaller massive corals, with their simpler shapes,
will be more able to survive a future of larger wave heights, but less able to support the
biodiversity of today’s coral reefs.89
For intertidal and coral reef environments, however, biological and physical
considerations prevent across-the-board predictions. First, wave forces vary throughout each
ecosystem, both predictably and unpredictably; with increasing wave heights in the future, this
variability will increase. For coral reefs, most dissipation of wave energy occurs within the first
fifty meters shoreward of a reef crest, dividing the reef into intense and more benign
hydrodynamic regions (i.e., the crest zone and flat zone).90 Increases in wave heights will
amplify the wave-force differences between these regions.91 For wave-swept shores, the
topography of subtidal and intertidal substrata leads to largely unpredictable variation in wave
forces.92 For example, on a two-hundred-meter stretch of shore “moderately exposed” to waves,
intertidal wave forces for a given offshore wave height can vary by nearly a factor of twenty
from microsite to microsite.93 Furthermore, as wave height increases, some locations will
experience greater wave-induced velocities and forces than today while others will not. At these
latter locations, bigger waves will simply break farther offshore, not affecting intertidal
velocities.94 Thus, as wave heights increase in the coming century, nearshore environments will
become more variable habitats: some sites will experience greater water velocities and
accompanying shifts in species abundances, while others will remain relatively unchanged.
A second consideration complicating predictions is “sublethal” damage of organisms due
to imposed forces, damage that does not kill organisms outright. Generally poorly understood,
this type of damage can accumulate over time and cause breakage in some cases.95 For example,
sublethal forces can cause formation of small cracks in seaweeds, eventually leading to breakage
if these cracks grow large enough.96 Increasing wave heights will inevitably cause greater
“chronic” damage of this sort, which either accumulates or becomes repaired. Exact predictions
of such damage, as well as the cost and speed of repair, are not currently possible although its
physiological toll may be great.
Finally, alteration of hydrodynamic properties in response to habitat conditions, as well
as natural selection, will allow today’s species to accommodate changing wave environments to
some extent.97 In many nearshore environments, organisms like seaweeds display greater
strength and/or more streamlined shapes where wave-induced velocities are larger.98 This
variability, along with natural selection, will allow some species to adapt to locales with great
Denny & Gaylord, supra note 84, at 5.
Madin, O’Donnell & Connolly, supra note 86, at 490, 492.
90
Madin, Black & Connolly, supra note 85, at 640-42.
91
Id. at 641.
92
Mark W. Denny et al., Extreme Water Velocities: Topographical Amplification of Wave-Induced Flow in the Surf
Zone of Rocky Shores, 48 LIMNOLOGY & OCEANOGRAPHY 1, 6 (2003); Helmuth & Denny, supra note 79, at 1338,
1343.
93
See Helmuth & Denny, supra note 79, at 1343 tbl.3.
94
See id. at 1338-39, 1344; MARK W. DENNY, BIOLOGY AND THE MECHANICS OF THE WAVE-SWEPT ENVIRONMENT
(1988).
95
Mach, supra note 81, at 961, 974-75.
96
Id. at 961, 973.
97
Brian Helmuth, Joel G. Kingsolver & Emily Carrington, Biophysics, Physiological Ecology, and Climate Change:
Does Mechanism Matter?, 67 ANN. REV. PHYSIOLOGY 177, 179, 185-87 (2005).
98
Emily Carrington, Seasonal Variation in the Attachment Strength of Blue Mussels: Causes and Consequences, 47
LIMNOLOGY & OCEANOGRAPHY 1723, 1723-24 (2002); Helmuth et al., supra note 97, at 185-86.
88
89
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ALL CLIMATE CHANGE IS LOCAL
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water velocities.99 Given the unprecedented pace of coming climate shifts, however, these
biological processes will likely fail to keep up in some cases. Where such plasticity and natural
selection are insufficient for surviving increased water velocities, populations or species will
disappear, with ramifications for entire ecosystems.100
In conclusion, to maintain nearshore ecosystems in the future, ocean protections like
marine protected areas and fisheries management should incorporate, along with other stressors,
the detrimental effects of increasing wave height on kelp forests, coral reefs, and intertidal
communities. Where coral reef species shift or kelp forests are displaced, marine protected areas
may require closer spacing to compensate for diminished reproduction and dispersal capacity,
and fisheries quotas may need to be reduced. For protections and management to be most
effective, long-term monitoring and short-term research are needed to elucidate patterns of
change. For example, short-term research should clarify the consequences of predicted increases
in variability, as some nearshore locations experience greater wave-associated forces and others
remain unchanged. Understanding how increased wave-force variability will affect the
occurrence, spacing, and reproduction of marine species up and down coastlines will in turn
enable managers to consider increasing wave height in reserve design, fisheries management,
and other ocean resource and coastal zone management policies.
VI. GAZING INTO THE CRYSTAL BALL: PREDICTING
THE FUTURE EFFECTS OF CLIMATE CHANGE
Biological systems are highly complex, and stressors may, in some cases, be difficult to
predict due to the highly nonlinear drivers of ecosystem processes.101 A precautionary, hedging
approach that attempts to preserve natural habitat wherever possible is therefore preferable
whenever practicable; however, given finite resources and the need to make explicit tradeoffs
between ecosystem services, science can serve as an effective source of information on rates of
damage, likelihood of recovery, and identification of other interacting forces that can be
controlled. Such knowledge allows managers to prioritize conservation and management efforts
as well as to seek control of interacting stressors such as pollution and fishing.102
Mechanistic ecological forecasting provides us with a predictive tool to anticipate the
location of ecosystems most (and least) susceptible to the impacts of climate change.103 It relies
upon an understanding of the mechanisms that cause organism and ecosystem response, applying
relationships between environmental factors (like terrestrial weather, water temperature, or pH)
and organism physiological responses (like body temperature, respiration rate, or energy
allocation) to predict spatial and temporal patterns of stress, mortality, and reproduction in
marine ecosystems as a function of present and future possible climate scenarios104 up to fifty
years in the future.105 Forecasts based on knowledge of physiological limitations can parse out
Helmuth et al., supra note 97, at 179.
Id.
101
Crain et al., supra note 26, at 1311.
102
See, e.g., Hoegh-Guldberg et al., supra note 28, at 345.
103
Michael Kearney & Warren Porter, Mechanistic Niche Modeling: Combining Physiological and Spatial Data to
Predict Species Ranges, 12 ECOLOGY LETTERS 334, 334-38 (2009).
104
Helmuth, supra note 2, at 753, 758.
105
Clark et al., supra note 27, at 657.
99
100
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which environmental stressors affect organisms the most,106 anticipate how organisms might
respond to novel conditions and new habitats,107 and provide information that might either favor
or limit mitigation strategies.108
In many cases, understanding what we cannot predict with confidence will be as
important as understanding what we can predict, as different levels of certainty may suggest
different management outcomes.109 An inherent property of ecological forecasts is that
predictions are accompanied by defined levels of uncertainty, similar to those provided for
weather forecasts110 and hurricane activity. Uncertainty may result from imprecise information
on climate, a lack of understanding of how changes in environment translate into physiologically
relevant parameters for the organism, high inherent variability in the responses of organisms, or
an inability to anticipate human reaction to the changing environment.111 When uncertainty is
high, policy decisions can incorporate the largest “buffering” capacity on a ratcheting-up basis in
order to account for rising uncertainty in what the future will hold. By focusing on
environmental stressors or specific ecosystems where the predicted repercussions of climate
change have high certainty, managers of marine ecosystems can identify and effectively mitigate
effects and can more effectively allocate limited resources.
The efficacy of mechanistic ecological forecasting approaches for predicting changes in
marine ecosystems in response to climate change has been demonstrated through the use of
retrospective analyses. For example, Wethey and Woodin accurately estimated shifts in the
geographic distribution of a barnacle species by identifying limitations of sea surface
temperatures on reproductive success.112 Such “hindcasts” do not include levels of all elements
of uncertainty associated with our ability to forecast future patterns of climate. However, they
suggest that physiological ecology and mechanistic ecological forecasting can provide a fruitful
approach for both understanding the implications of climate change for marine organisms and
applying this knowledge to create solutions to effectively manage and conserve coastal and
oceanic ecosystems. Although there are clear advantages to predicting climate change impacts
using mechanistic ecological forecasting compared with only using knowledge of current and
future habitat conditions, application of this tool requires physiological knowledge of the target
species or populations. Detailed physiological data may be unavailable in certain cases,
requiring additional experimentation and time to establish species- or population-specific
performance curves. As hopefully detailed here and illustrated by the three scenarios, such
knowledge is critical to success.
VI. CONCLUSIONS
106
Martin Wikelksi & Steven J. Cooke, Conservation Physiology, 21 TRENDS IN ECOLOGY & EVOLUTION 38, 40
(2006).
107
Michael Kearney et al., Modeling Species Distributions Without Using Species Distributions: The Cane Toad in
Australia Under Current and Future Climates, 31 ECOGRAPHY 423, 431-32 (2008).
108
Nicola J. Mitchell et al., Predicting the Fate of a Living Fossil: How Will Global Warming Affect Sex
Determination and Hatching Phenology in Tuatara?, 275 PROC. ROYAL SOC’ Y B 2185, 2186 (2008).
109
Robin Gregory & Graham Long, Using Structured Decision Making to Help Implement a Precautionary
Approach to Endangered Species Management, 29 RISK ANALYSIS 518, 520-22 (2009).
110
Clark et al., supra note 27, at 657-58.
111
Id. at 659.
112
David S. Wethey & Sarah A. Woodin, Ecological Hindcasting of Biogeographic Responses to Climate Change in
the European Intertidal Zone, 606 HYDROBIOLOGIA 139, 146 (2008).
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The effects of climate change on natural ecosystems are highly complex, and scientists
are fighting a battle against time to predict where, when, and with what magnitude the impacts
are likely to occur. Mitigation of the anthropogenic drivers of climate change remains as a high
priority; however, adaptation to the inevitable impacts of global climate change on natural and
human-managed ecosystems is also of key importance. An understanding and application of
physiological ecology can help managers to predict ecological responses. Several key
recommendations emerge from the examples described in this paper. First, global climate
change (changes in temperature, salinity, pH and wave heights) interacts with other, nonclimatic,
factors to drive stress and mortality. Thus, even in cases where physical variables related to
climate change (e.g., temperature) cannot be altered, organisms and ecosystems may, in some
cases, be prevented from reaching tipping points by reducing other stressors like
overexploitation, nutrient runoff and habitat destruction. Second, the impacts of climate change
vary considerably in space and time, and between species. Accordingly, there will be “winners”
and “losers,” including commercially important and invasive species. Through the use of
bioenergetic budgets to inform fisheries stock assessments and mechanistic ecological
forecasting techniques, it may be possible to identify target species and specific locations where
climate change is most (and least) likely to have an effect, and in doing so, guide management
decisions. For example, understanding the likely location of impacts on fisheries can help to
guide future economic responses to climate change. Finally, as demonstrated in studies of
thermal stress in rocky intertidal invertebrates and wave stress in seaweeds, while extreme events
lead to mortality, more subtle changes in the environment can lead to population declines as
well, making the absolute detection of change difficult. Monitoring ecological responses to
climate change should be a part of any marine resource management program, and should
include an investigation of the mechanisms driving the observed change. By viewing the world
through nonhuman eyes, we may better be able to understand how climate change will affect our
food, our environment, our safety, and our livelihoods, and in doing so, more effectively
concentrate efforts to reduce damage wherever possible.
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Figures
Figure 1. An example of a generic thermal performance curve, showing some aspect of
physiological performance (for example, growth, reproduction or fitness) as a function of body
temperature. Response curves vary from species to species, but all typically display some
optimum (Topt) at which performance is maximized (Pmax), as well as critical minima (CTmin) and
maxima (CTmax) beyond which mortality and/or reproductive failure occur. When combined
with knowledge of how body temperature varies, thermal performance curves can be used to
determine how close an organism is living relative to its thermal optima and thresholds under
current and future conditions of climate change.113
113
Adapted from Angilleta, Thermal Adaptation: A Theoretical and Empirical Synthesis, supra note 9, at 38;
Michael J. Angilleta et al., Coadaptation: A Unifying Principle in Evolutionary Thermal Biology, 79
PHYSIOLOGICAL AND BIOCHEMICAL ZOOLOGY 286 (2006).