Mach, M.E., S.G. Reiter & L.H. Good. 2015. Managing a mess of cumulative effects: linking science and policy to
create solutions. Current: The Journal of Marine Education 29(1):26-31
Slide Narrative for A. Science 101: Challenges of assessing cumulative effects
Developed by Megan E Mach, February 2015
Center for Ocean Solutions
Slide
No.
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Title
Narrative
Title
Challenge:
ecosystem
complexity
Title slide, goals.
Ecosystems are filled with complex interactions between species, their
habitats, and their resources. Direct and indirect impacts to this
complexity, connecting impacts back to their sources, describing impact
interactions, and defining change are challenges associated which
understanding cumulative effects to these systems.
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Direct vs.
indirect
impacts
We already know the relationship is not as simple as a human
activity (such as flushing a toilet) produces a stressor (nutrients)
that impacts an ecosystem component – such as a species or
habitat (in the case of nutrients, a regular number of toilet flushes
probably won’t result in anoxic zones on the coast). But we know
this relationship to be much more complex. [Each bullet
represents a new build to the original slide]
I am going to illustrate this complexity using an example from an
assessment done in the northeast Pacific in Puget Sound, Washington.
In this estuary seagrass, Zostera marina, has a positive effect on crab,
salmon and herring species by acting as a nursery ground.
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Where do
stressors
When seagrass beds are stressed by pollutants like PCBs and
heavy metals, these pollutants have direct negative effects on the
seagrass, and indirect effects on other species.
As well as direct effects on those species
Those direct and indirect effects can feed up the food web and
impact top predators that feed on those herring and salmon
species, and potentially impact the crab and salmon fisheries
common to this region. But as you probably expect, there is more
than one stressor, that also had direct and indirect impacts
Shoreline armoring and other toxic contaminants both have
negative impacts on seagrass. Which as you might expect, can
have direct and indirect effects on the rest of the foodweb.
This is a challenge, but ecosystem scientists are doing this
research. We understand that these are complex systems and want
to know how these many stressors interact and impact species and
habitats in our coastal oceans.
However, a major gap in our work is located up stream of the stressor.
What is creating it?
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Mach, M.E., S.G. Reiter & L.H. Good. 2015. Managing a mess of cumulative effects: linking science and policy to
create solutions. Current: The Journal of Marine Education 29(1):26-31
originate
Understanding the location and amount of a stressor being produced is
important for predicting when and how long a stressor might interact with
the environment.
 This study is part of a larger risk assessment done by Jameal
Samhouri and Phil Levin. And serves as a good example of a
method that can be used to quantify relationships between species
and stressors
Another challenge, beyond direct/indirect relationships, and tying a
stressor back to its source lies in the interaction between multiple impacts.
 For example – what happens to the system when it receives both
pollutants and physical disturbance at the same time?
A study looking at impact interactions, Caitlin Crain, Kristy
Kroeker and Ben Halpern in 2008, identified the effects of many
pairs of interactions – though not specifically these two. They did
however…
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Interactions
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Interaction
example
Look at the effects of a different kind of disturbance on oyster reefs:
fishing and hypoxia (low oxygen levels)…
 Both have a direct negative effects on Oyster survival. But,
 But together their effect is much stronger, producing a synergistic
effect on the oyster reef as well as the abundance of species that
live in this habitat. But here in lies another challenge to ecology,
studies have started looking at pairs of impacts, maybe three
together, but to do more seems next to impossible if you want to
have a statistically rigorous test.
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Ecosystem
change
Understanding the effect of stressors on species, populations and
ecosystems requires understanding how these ecosystems respond to
cumulative stress
 In the past, if we wanted to understand how elements of an
ecosystem respond to stress, we test it against a uni-dimensional
pressure or stress on the environment (such as herbivory on algae
growth) While at low stressor levels an ecosystem functions
normally and remains unstressed,
 As the stressor increases the ecosystem because less able to
function (becomes more stressed).
 Developing production functions like this can help describe how
an ecosystem will respond as it accumulates more stress and
whether its response is linear or non-linear, rapid or slow.
 But the way managers need to manage, whole ecosystems and
many stressors, means that the relationship between many
stressors and the environment need to be predicted. Which can
begin to answer questions like: When does this ecosystem shift?
And, are there certain species that respond first? Understanding
the complexity of ecosystem dynamics is necessary for
understanding how whole ecosystems respond to threats from
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Mach, M.E., S.G. Reiter & L.H. Good. 2015. Managing a mess of cumulative effects: linking science and policy to
create solutions. Current: The Journal of Marine Education 29(1):26-31
human activities. But these interactions are not static, they vary in
time and across geographic regions.
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Challenge:
Temporal
change
Ecosystems have been responding to human impacts for many centuries,
including historic activities and impacts when evaluating the status of
today’s ecosystems and predicting future impacts is both a challenge and
a necessity if we are to understand how ecosystems respond to cumulative
effects.
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Including
historical
change
Cod in the northwest Atlantic have been fished below sustainable
numbers.
 If we were to only look at the past 50 years of data, it might be
easy to conclude that this is normal (the slope of the red line is
flat), but in this historical study done by Karen Alexander and
colleagues
 They demonstrated that historic landings were up to 8 or 9 times
the numbers we see in more recent years. Methods that incorporate
historic data will allow for a more accurate portrayal of population
level impacts. This kind of finding is becoming more common in
recent literature and has been found in:
 Other examples: predatory fish around the globe, green turtles in
the Hawaiian archipelago, and for sea otters in the Aleutian
Archipelago in the North Pacific
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Challenge:
Spatial
complexity
Similarly, ecosystems respond to unique conditions that vary over small
spatial scales as a result of spatial differences in environmental
conditions, species interactions, and human activities. Identifying where
stressors occur and how impacts vary across species ranges and life
histories remains a major challenge.
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Spatial
complexity:
Species &
Stressors
Species like salmon, that travel between many habitats during their lives,
are subject to threats from humans that differ across their ranges that
affect them in different ways across their life-cycle. Here is an example of
the Fraser River Sockeye Salmon migration route in the northeast Pacific
 Eggs are hatched upstream, fry swim to estuaries on the coast, and
from their north past Vancouver Island and into the Pacific Ocean
from where they return a number of years later to lay their eggs in
the same rivers and streams they were hatched in. And along this
whole transitory life-cycle, each stage is subject to different
impacts, from sedimentation and dams in the rivers, to pollution
as they pass city centers and overfishing as they head out to sea.
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Spatial
complexity:
How do we begin to predict where stressors enter the environment and
how they impact species and habitats? We are just beginning to
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Mach, M.E., S.G. Reiter & L.H. Good. 2015. Managing a mess of cumulative effects: linking science and policy to
create solutions. Current: The Journal of Marine Education 29(1):26-31
Modeling
Impacts
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Shifts may
become
difficult to
reverse and
growing
more
common
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Where the
science is
moving
forward
understand these broad scale relationships between stressor ranges, and
how species respond to these stressors across their life histories and
within their ecosystems.
 One way this is being tackled is through spatial modeling – 1st.
mapping the area where stressors occur in marine environment
 And mapping where marine habitats are in those same regions.
These studies include assessments of how vulnerable habitats and
species are to those stressors and multiply the two for every 1km2
pixel to come up with an impact score for each pair. These are
then added together to come up with…
 A cumulative impacts map that shows hotspots where species and
habitats are highly impacted.
 Studies like these, that model the relationship between where
stressors occur and their intensity and how habitats respond, are an
excellent first step in demonstrating these overlapping issue.
Impact models have been completed along the California Current,
along the coast of British Columbia, and for the entire
Mediterranean.
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With climate change and rising anthropogenic pressures on natural
resources, ecosystem shifts seem to be growing more common.
And we know from experience that many of these shifts are very
difficult if not impossible to reverse over reasonable timescales.
This gives us all the more reason to try to understand and be able
to predict these complex relationships in order to try to avoid or
mitigate their negative consequences.
So where are we and where do we go.
 Ecosystem complexity – Advancing our understanding of
ecosystem complexity involves continuing to develop field studies
and lab experiments that ask questions about how humans impact
food webs and coastal habitats, improving predictive models and
developing ecological indicators that will help indicate when an
ecosystem is becoming too stressed to function properly.
 Research scientists are accomplishing these goals, slowly but
surely. But with temporal and geographic scale there is still room
for improvement.
 Temporal scale – Develop more open access data sets and ask
question that compare not only ongoing pressures, but include
what we know about impacts from historic ones.
We need to share our data. Why don’t we? This is hard earned
data and we are protective of it. That’s fair, careers are built on
collecting and processing these data. But to be able to ask
questions on change over time, or how regions differ we need to
share. And this is progressing with open access data required by
some journals, electronic supplemental sections that can include
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Mach, M.E., S.G. Reiter & L.H. Good. 2015. Managing a mess of cumulative effects: linking science and policy to
create solutions. Current: The Journal of Marine Education 29(1):26-31
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Further
resources
raw data and public databases like Driad that can store data sets.
Geographic scale - For geographic scales we need monitoring that
assesses impacts at multiple scales to better inform local scale
management. Filling the gap between activities producing
stressors, and the impact those stressors have are necessary for
defining spatial impacts. But why don’t scientists ask these
questions? Well some do it well, but most of us don’t. I think there
are three key reasons. 1) it’s hard, 2) who funds monitoring work?,
3) little prestige, no glory. There is a need to understand and
promote the value in this type of research
Link to teaching resources at COS, presentation development and contact
information, and project funders.
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