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Abstract

While they can be useful tools to support decision-making in ecosystem management, robust simulation
models of ecosystems with alternative states are challenging to build and validate. Because of the possibility
of alternative states in model dynamics, no trivial criteria can provide reliable and useful metrics
to assess the goodness-of-fit of such models. This paper outlines the development of the model TRITON,
and presents simulation-based validation and analysis of model sensitivity to input parameters. TRITON
captures the local dynamics of seaweed-based rocky reef communities in eastern Tasmania, which now
occur in two alternative persistent states: (1) either as dense and productive seaweed beds, (2) or as sea
urchin ‘barrens’ habitat, i.e. bare rock largely denuded of macroalgae and benthic invertebrates due to
destructive grazing by sea urchins. Pattern-oriented-modelling, i.e. comparing patterns in model dynamics
across Monte–Carlo simulations with direct observations of Tasmanian reef communities over large
scales, provides a valuable approach to calibrate the dynamics of TRITON.
Using the computationally efficient, model-independent extended Fourier amplitude sensitivity test,
we identify fishing down of predatory lobsters, sea urchin recruitment rate, as well as seaweed growth
rate as key parameters of influence on overall model behaviour. Through a set of independent sensitivity
tests, we isolate different sets of drivers facilitating the ‘forward’ shift from the seaweed bed to the
urchin-dominated state, and the reverse or ‘backward’ shift from denuded sea urchin barren to recovery
of seaweed cover. The model suggests that rebuilding populations of large rock lobsters, which predate
the urchins, will be effective in limiting ongoing formation of sea urchins barrens habitat, but that the
chances of restoring seaweed beds from extensive barrens are relatively low if management relies solely
on rebuilding stocks of large rock lobsters. Moreover, even when it does occur, seaweed bed restoration
takes up to three decades in the simulations and so is arguably unrealistic to implement under short-term
fishery management plans. The process of model validation provided both a better understanding of the
key drivers of community dynamics (e.g. fishing of predatory lobsters), and an assessment of priority
areas for future research.

Item Type:	Article
Authors/Creators:	Marzloff, MP and Johnson, CR and Little, LR and Soulie, JC and Ling, SD and Frusher, SD
Journal or Publication Title:	Ecological Modelling
ISSN:	0304-3800
DOI / ID Number:	https://doi.org/10.1016/j.ecolmodel.2013.02.022
Additional Information:	Copyright 2013 Elsevier
Item Statistics:	View statistics for this item

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