funded by nato oyster reefs are complex ecological systems because they:
TRANSCRIPT
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
Detritus
Micro-biota
Preda-tors
Deposit feeders
Meio-fauna
Are far from equilibrium
Free Energy
Reaction Coordinate
EquilibriumDeath
Death
Life
Steady State Excessive
disorder,too much change
Excessive order,rigid,no change
Turbidity
Human Impact
Benthic or Pelagic Food Web Alternate Equilibria
Benthic
PelagicExhibit alternate equilibria
Demonstrate feedback
REEF
Clump
Larvae and spat
Display evidence of self-organization
Show emergence
Connections or flows are non-linear
50%
Power
Efficiency
max
max
R = Wt 0.75
R = Respiration Rate
Wt = body weight
10
1.05
0.001 1.0
Relationships may exist across multiple scales
Systems evolve for high production (max. power principle) and are highly optimized for tolerance (HOT)
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
Oyster
Density
E1E2
Environment
Oysters
No Oysters
Traditional - Environmental Conditions Changed to Historical Levels
Recovery Collapse
Recovery and collapse trajectories are the
same or very similar
But, sometimes the recovery is unpredictable and the original state is not achieved.
The system shifts to an alternate state.
System
state
S1
S2
E1 E2Environment
Oysters
Plankton
Complex Systems Approach : Alternate States
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.
System state
S1
S2
E1 E2Environment
Oysters
Plankton
Collapse
Engineered – Oysters added
Historical environment not restored, system
contiinues to collapse
System state
S1
S2
E1E2
Environment
Oysters
Plankton
Collapse
Engineered - Feedbacks identified and manipulated
Recovery
Historical environment restored and system returns by different trajectory to original
state
System state
S1
S2
E1E2
Environment
Oysters
Plankton
Engineered - Feedbacks identified and manipulated
Collapse
Recovery
Feedbacks
Understanding of feedback controls allows near direct reestablishment of
original state
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.