Download Oyster Reef Restoration:

Funded By
NATO
Oyster reefs are complex
ecological systems because
they:
• Are open systems
• Are composed of
multiple interacting
components
• Are hierarchically
structured
• Exhibit dissipative
structures
Filter
feeders
Predators
Detritus
Deposit
feeders
Microbiota
Meiofauna
Are far from
equilibrium
Life
Free
Energy
Steady
State
Excessive
order,
rigid,
no
change
Excessive
disorder,
too much
change
Death
Death
Equilibrium
Reaction Coordinate
Exhibit alternate
equilibria
Benthic
Benthic or Pelagic Food
Web Alternate Equilibria
Pelagic
Human
Impact
Turbidity
Demonstrate
feedback
Larvae
and
spat
Display evidence of
self-organization
Show emergence
Clump
REEF
R = Respiration Rate
10
Connections or
flows are non-linear
Relationships may
exist across
multiple scales
Systems evolve for
high production (max.
power principle) and
are highly optimized
for tolerance (HOT)
R = Wt 0.75
1.05
0.001
Wt = body weight
1.0
max
Power
50%
Efficiency
max
HOT Systems
• Are robust, yet fragile
• Unlike SOC systems where massive fluctuations occur
as a result of the natural system dynamics, HOT
systems are hypersensitive to new environmental
perturbations that were not part of the systems
evolutionary history (catastrophic or anthropogenic)
• HOT systems demand a change in research strategy
from confirming negative effects to determining if a
system can survive proposed changes (robust enough)
before they happen
The preceding attributes support the contention that
oyster reefs are complex systems, that is, they are
composed of a large number of interacting
components that are observable across many scales
and their dynamics are non-linear (causes are not
proportional to consequences). Thus, such systems
are often unpredictable.
In this context, how does complexity influence oyster
reef restoration?
Restoration: A complex
systems view
Ecological Restoration
Restoration attempts to return an
ecosystem to its historic trajectory.
Traditional Approach To
Restoration
• Assumes the organisms via succession
will rebuild the original system
• But, first, the historical environmental
or disturbance regimes must be
reestablished
Traditional - Environmental Conditions
Changed to Historical Levels
Oyster
Oysters
Density
Recovery
Recovery and collapse
trajectories are the
same or very similar
No Oysters
E1
E2
Environment
Collapse
But, sometimes the recovery is
unpredictable and the original state is
not achieved.
The system shifts to an alternate state.
Complex Systems Approach :
Alternate States
System
state
Oysters
S1
S2
Plankton
E1
Environment
E2
The Complex Systems Approach
to Restoration
• Assumes the reference or pristine system used for
comparison is a complex system.
• Considers the degraded system as an alternate state
that is very different from the natural or pristine
state.
• Recognizes that the trajectory to degradation is
often different from the pathway to recovery, usually
due to ecological constraints that cause internal
feedbacks.
• Focus is on identifying the ecological constraints
and feedbacks, using experiments (including
simulation models), comparative synthetic analyses,
scenario analysis, etc.
• Determine if the system is robust to potential
changes.
• Finally, the constraining feedbacks are disrupted and
the system is engineered toward the desired state.
Engineered – Oysters added
System
state
Oysters
S1
Collapse
Historical environment
not restored, system
contiinues to collapse
S2
Plankton
E1
Environment
E2
System
state
Engineered - Feedbacks identified and
manipulated
Oysters
S1
Historical environment
restored and system
returns by different
trajectory to original
state
Recovery
S2
Plankton
E1
Environment
E2
Collapse
System
state
Engineered - Feedbacks identified and
manipulated
Oysters
S1
Feedbacks
Collapse
Recovery
S2
Understanding of
feedback controls
allows near direct
reestablishment of
original state
Plankton
E1
Environment
E2
Features of complex ecological
systems that make them a
management challenge
• Feedback vs. Direct Controls
• Non-linear vs. Linear Connections
• HOT vs. SOC
All of which leads to
Surprise
Very Large LINKS
Thieving LINKS
Suggests a research strategy
that:
• Determines the control mechanisms
• Encourages scenario development no
matter how extreme (think outside of the
box approach)
• Promotes the building and use of
simulation models as experimental test
beds
• Is long term in scope, as the environment
is constantly changing
It’s A Non-linear World!
Be Prepared. Plan Ahead.
NOTES
Restoration Evaluation
• Direct comparison of selected parameters
are determined or measured with regard to a
reference site.
• Attribute analysis compares via modeling the
attributes of the restored and reference
systems.
• Trajectory analysis interprets time series of
comparative data to determine trends.
Recovery and Restoration
• An ecosystem has recovered – and is
restored – when it contains sufficient
biotic and abiotic resources to continue
its development without further
assistance or subsidy. It will sustain
itself structurally and functionally. It
will also demonstrate resilience to
normal ranges of environmental stress
and disturbance.
Attributes of Restored Ecosystems
• Contains characteristic assemblage of species with
regard to the reference system.
• Consist of indigenous species to the greatest
practicable extent.
• All necessary functional groups are represented.
• The physical environment is capable of sustaining
reproducing populations.
• The restored system functions normally/
• It is suitably integrated into the next larger
ecological scale.
• Potential threats to its health and integrity have been
essentially eliminated.
• Is resilient to normal environmental conditions.
• The ecosystem is self-sustaining to the same degree
as the reference system.