funded by nato oyster reefs are complex ecological systems because they:

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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.

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