11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 20: Modeling Concepts and Processes on Coral Reefs
20-5
Agent-based Simulation of a Recreational Coral Reef Fishery: Linking Ecological
and Social Dynamics
Jennifer SHAFER* 1
1 University of Hawaii, Honolulu, HI
In this agent-based simulation, the ecological dynamics of a simple coral reef ecosystem
are linked to the social dynamics of a recreational fisher community. The simulation
captures the interaction and dynamic feedback between the ecological and social systems
and how these affect fish stocks and fisher behavior. The analysis reveals the complex
nature of how system-level dynamics emerge from localized individual-level behaviors.
Empirically based parameter estimates and behaviors drive the energetics and ecology of
the reef’s three trophic levels from the bottom-up through individual-based mechanistic
rule-sets: photosynthetic turf algae grows, herbivorous fish graze while schooling and
avoiding predation, and roaming piscivores hunt herbivores and patrol the reef edge.
These simple individual behaviors give rise to the more complex ecological phenomena
of fish schooling, carrying capacity, and population cycles. At the same time, a
community of recreational fishers interacts with each other and the physical and
biological components of the reef. Individual fishers assess risk and pay-off in deciding
when to go fishing, find appropriate locations on the reef to set gear, and attempt to catch
fish. Simple individual choices made in the dynamic reef environment result in the
emergent sociological phenomena of localized resource depletion, diffusion of
information and cooperation. Under a community-based management scenario where
fishers have the choice to form self-organized coalitions to establish and enforce catch
restrictions, the resource dilemma associated with overfishing can be overcome under
certain conditions. This research provides proof-of-concept for using agent-based
simulation as a versatile and powerful modeling tool for coupling biophysical and
sociological processes and evaluating alternative management scenarios.
20-6
Models of Coral Reefs with And without Macroalgae Indicate Differential Resilience
to Fishing And Anthropogenic Nutrients
Tak FUNG* 1 , Robert SEYMOUR 1 , Craig JOHNSON 2
1 Department of Mathematics, University College London, London, United Kingdom,
2 School of Zoology, University of Tasmania, Hobart, Australia
A dynamic model of a generic coral reef ecosystem is constructed using differential
equations. Three benthic groups (corals, turf algae and macroalgae), three fish groups
(herbivorous and small and large piscivorous fish) and one invertebrate group (sea
urchins) are modeled.
The model is parameterized for a pristine (no fishing) generic reef with and without
macroalgae using data from the Caribbean and Indo-Pacific. Three scenarios are
examined, viz. increased a) fishing pressure, b) nutrients, and c) fishing and nutrients.
Nutrients increase the growth rates of both macroalgae and turf, but can have a much
bigger impact on reefs with macroalgae, since macroalgal patches grow laterally over
other benthic groups.
For the reef without macroalgae, increased fishing pressure can give a continuous phase
shift from high coral cover to high cover of turf algae. The reef with macroalgae can
exhibit both continuous and discontinuous phase shifts to dominance by algae (turf and
macroalgae) as fishing pressure increases. Increased nutrients also promotes algal cover,
and for reefs which exhibit a discontinuous phase shift as grazer biomass decreases,
nutrients can increase both the hysteresis effect (which slows recovery of coral cover)
and the grazer biomass at which such a phase shift occurs. Fishing and nutrients can
interact synergistically, such that a heavily fished reef with high nutrients can have high
algal cover where in the presence of either factor alone, it would have low algal cover.
However, in some cases, either decreased grazing or increased nutrients alone can result
in high algal cover.
The results suggest the need for different management strategies for mitigating the effects
of fishing and nutrients on reefs with macroalgae (such as many in the Caribbean) and
without macroalgae (such as typical offshore Indo-Pacific reefs).
20-7
Managing Uncertainties in The Development Of An Agent-Based Model Of A Complex
Coral Reef Ecosystem
Felimon GAYANILO* 1 , John MCMANUS 1
1 National Center for Coral Reef Research, RSMAS, University of Miami, Key Biscayne, FL
Agent-based modeling (ABM), an element of the Science of Complexity, is gaining acceptance
in main stream ecological science as a viable tool to model complex coral reef ecosystems.
Current approaches in agent-based modeling to simulate ecological changes due to
anthropogenic and/or natural disturbances in a complex system, such as coral reef ecosystems,
rely heavily on our ontological and epistemological understanding of the ecological network.
Initialization of the model is inductive and generally, environment and rules are modified and
the emergent behavior of the global system is analyzed. Coral reef science is just beginning to
understand the linkages and taxonomic attributes of the elements of this diverse and complex
ecosystem. These uncertainties and information gaps force researchers to rely heavily on
assumed biophysical, temporal, physiological, and sociological rules. This paper addresses the
effects of some of these uncertainties by comparing results of simulated scenarios executed by
an ABM simulation tool, GAMET (Geographic Agent-based Marine Eco-forecasting Tool).
Moreover, options are presented as to how to minimize the effects of these uncertainties,
including the strengthening of a global interdisciplinary program, CARRUS (Comparative
Analysis of Reef Resilience Under Stress).
20-8
Thresholds And The Resilience Of Caribbean Reefs Under Climate Change
Peter MUMBY* 1
1 School of BioSciences, University of Exeter, Exeter, United Kingdom
The deteriorating health of the World’s coral reefs threatens global biodiversity, ecosystem
function, and the livelihoods of millions of people living in tropical coastal regions. Reefs in the
Caribbean are among the most heavily-impacted, having experienced mass disease-induced
mortality of the herbivorous urchin Diadema antillarum in 1983 and two framework-building
species of coral. Declining reef health is characterised by increases in macroalgae. A critical
question is whether the observed macroalgal bloom on Caribbean reefs is easily reversible. To
answer this question, we must resolve whether algal-dominated reefs are an alternative stable
state of the ecosystem or simply the readily reversible result of a phase change along a gradient
of some environmental or ecological parameter. Here, using a fully-parameterised simulation
model, we show that Caribbean reefs became susceptible to alternative stable states once the
urchin mortality event of 1983 confined the majority of grazing to parrotfishes. We reveal
dramatic hysteresis in a natural system and define critical thresholds of grazing and coral cover
beyond which resilience is lost. Most grazing thresholds lie near the upper level observed for
parrotfishes in nature suggesting that reefs are highly sensitive to parrotfish exploitation.
Ecosystem thresholds can be combined with stochastic models of disturbance to identify targets
for the restoration of ecosystem processes. We illustrate this principle by estimating the
relationship between current reef state (coral cover and grazing) and the probability that the reef
will withstand moderate hurricane intensity for two decades without becoming entrained in a
shift towards a stable macroalgal-dominated state. Such targets may help reef managers face the
challenge of addressing global disturbance at local scales.
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