NetLogo User Community Models

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## ## WHAT IS IT?

This model was set up to provide a working conceptual model of coral reef dynamics in the face of climate change. Climate change threatens a wide range of ecosystem processes that underpin the world's coral reefs. The implementation of conservation actions to manage fishing pressure and water quality has already shown resilience benefits, however ongoing public support is critical to ensure these and future actions can successfully counter the deleterious effects of climate change. Public understanding of resilience theory and the complexity of stochastic events effecting coral reefs is limited, in part, by the model format presented. Here we present a model used as a basis for the simple game known as ‘Snakes and Ladders’ to assist in the understanding of resilience potential and stochastic events in coral reef ecology.

## ## HOW IT WORKS

The simplicity of the game is the essence of why we selected it. We used a 10 by 10 checkered board numbered sequentially from 1 to 100. The lower numbers represent an unspecified state that is poor (low coral cover or low biodiversity or low resilience) while the higher numbers represent the healthiest state a reef can achieve. Therefore each player’s chip can represent a coral reef within a common region in order to minimize environmental heterogeneity. Each player starts at the lowest number and using the dice values of 1 to 6 precede along the board. With a slight twist on the original game the number of moves required to reach the final square is the measure of success.
However the game is complicated by the addition of ‘snakes’ and ‘ladders’ that either accelerate or retard a ‘coral reef’ chip’s progress. Without these complications each ‘coral reef’ chip would take between 17 (17 x 6 moves = 102 squares) and 100 (100 x 1 move =100 squares) moves and winning would simply be a game of lucky dice rolls. With the inclusion of snakes and ladder elements the layout of the board will determine the minimum number of moves possible. Snakes can represent many different processes (over fishing, disease, Acanthuses planci outbreaks, cyclones, thermal bleaching, shipping disaster etc.) that span from retarding growth (perhaps a small magnitude that is less than dice throw) or severely reducing coral reef health (large magnitude). Likewise the ladders can be used to represent a combination of management actions and natural conditions including marine reserves, shipping control, anchoring protection, strong recruitment, and favorable growth conditions etc.

## ## HOW TO USE IT

The player has the option of firstly selecting the number of snakes and then ladders. The mean size of the snakes/ladders is also altered if desirable. The player can then keep throwing a single dice and watch the movement of the coral reef step by step. Otherwise they can run many thousands of games (as specified) by a click of a button.
The outputs show the number of games that were completed with a specified number of dice rolls. Clearly the faster the coral reef can complete a 'game' the more resilient it is to bounce back from disasterous events. Ladders can help here but are often hard to implement in practise. Climate change is rapidly adding more snakes.

## ## THINGS TO NOTICE

Notice how the coral reefs can end up oscillating at a lower state if the number of snakes is just too many.

## ## THINGS TO TRY

Try playing with the size of the snakes and ladders.

## ## EXTENDING THE MODEL

Clearly this model is not trying to inform scientists about the dynamics of coral reef growth but the model could be extended by making the players more adaptable and perhaps more interactive.

## ## NETLOGO FEATURES

We placed a picture of coral reefs in the background to provide some interesting context. Ideally we would have liked better looking snakes and ladders but this proved very difficult to code up.

## ## CREDITS AND REFERENCES

This model was created from discussons held at the Great Barrier Reef Marine Park Authority in 2012.
Lead netlogo coder was Stefan Dulman with some assistance from Stuart Kininmonth. Graphics were the artistic effort of Dieter Tracey and climate change orientation was from Roger Beeden and Stuart Kininmonth. This model is part of an effort to educate the public on climate change.
The implications are discussed in a paper titled "Snakes and Ladders: Resilience modeling of coral reef ecosystems for public education " by Kininmonth, Stuart, Beeden, Roger , Dulman, Stefan & Dieter Tracey pubished in Journal of Environmental Education 2013.
Questions concerning the model can be directed at stuart.kininmonth@stockholmresilience.su.se

This model is provided free and without limits to non-profit applications.