Alvarez-Filip, L.

Bozec, Y-M.

Mumby, P.J.

English

Aquatic Commons

Proceedings of the 65th Gulf and Caribbean Fisheries Institute                  November 5 – 9, 2012   Santa Marta, Colombia 
Modelling the Response of Reef Rugosity and Fish Assemblages  
to Climate Change in the Caribbean 
 
Modelando la Respuesta de la Rugosidad del Arrecife y  
las Comunidades de Peces al Cambio Climático en el Caribe 
 
Modéliser les Effets du Changement Climatique sur la Rugosité du Substrat  
et les Assemblages de Poissons dans les Récifs Coralliens des Caraïbes  
 
YVES-MARIE BOZEC1,2, LORENZO ALVAREZ-FILIP3,4, and PETER J MUMBY1,2 
1Marine Spatial Ecology Lab, School of Biological Sciences, University of Queensland, St. Lucia, Qld 4072, Australia. 
2College of Life Sciences, University of Exeter, Exeter, EX4 4PS, United Kingdom. 
3Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6 Canada. 
4Healthy Reefs Initiative, 1755 Coney Drive, Belize City, Belize. 
 
EXTENDED ABSTRACT 
A striking feature of coral reef habitats is their topographical complexity which is generated by the growth and 
calcification of reef-building corals. Highly rugose reefs typically support abundant and diverse biological communities 
which in turn provide many services to the ecosystem. In the Caribbean, such reefs were found in areas dominated by corals 
with complex morphological forms, such as branching Acropora, or large Montastraea colonies which generate high 
structural relief. Due to multiple disturbances, the recent decades have seen a major decline of these structural species 
across the Caribbean, resulting in a global loss of reef rugosity. As the disturbance regime on Caribbean reefs is expected to 
rise with climate change, there is increasing concern about the future quality of coral reef habitats and the consecutive 
impacts on reef-associated organisms. We developed a model of coral reef ecosystems to predict future changes in reef 
rugosity and potential responses of fish assemblages in the Caribbean. The model is presented here, with emphasis on (1) 
model assumptions and parameterisation, (2) calibration and validation and (3) preliminary results of model simulations. 
The modelling approach is based on a spatially-explicit model of coral population dynamics (Mumby 2006, Mumby et 
al. 2006) of a typical Caribbean fore-reef system under acute disturbances (hurricanes and coral bleaching). The model 
represents a reef as a regular square lattice of 20 x 20 cells, each approximating 1m2 of reef substrate and comprising 
different species of corals and algae. Corals are stylised by a disk which represents the planar area of the colony. Empirical 
relationships allow estimating colony height, surface area and volume from colony diameter, based on the assumption that 
corals have a dome-like shape. When corals grow, their radial extension is converted into height extension so that colony 
surface area (and volume) increases. When a coral dies, the carbonate skeleton is progressively eroded so that colony 
volume (and surface area) decreases. Reef rugosity is then estimated at each time step by the contribution of living and dead 
coral colonies to the actual surface area of the reef bottom. As a result, rugosity increases with coral growth but is reduced 
by the bioerosion of dead colonies. 
The model was calibrated using data from Cozumel reefs, Mexico. Data on coral colony collected in situ showed (1) 
that colony height can be reliably predicted by colony diameter and (2) that a dome-like shape is a good proxy of the 3D 
geometry of many coral species, including the massive Montastrea species but also sub-massive forms such as Agaricia 
agaricites and Porites astreoides. The model was then evaluated against historical surveys (1984 – 2008) of coral cover in 
Cozumel compiled from published articles and reports. The global trajectory of coral cover was re-constructed using six 
coral populations and the disturbance regime observed during this 25 years period, with the occurrence of three hurricanes 
(Gilbert in 1988, Emily and Wilma in 2005) and two bleaching events (1998 and 2005). The re-constructed trajectory of 
coral cover was in good agreement with observations, capturing periods of decline and recovery after disturbance. In 
Cozumel, coral cover has globally declined from about 35% in 1984 – 1987 down to 15% in 2007 – 2008, and the model 
predicted a concomitant decline in reef rugosity from 2.3 to 1.5 units. Similarly to empirical observations, modelled coral 
cover and rugosity were highly correlated. 
By providing an explicit and dynamical representation of the 3D structure of individual coral colonies, this mechanistic 
model offers new perspectives for modelling coral reef ecosystems. In particular, the model can be used to produce future 
predictions of reef rugosity and fish biodiversity in response to climate change. To this aim, coral dynamics were simulated 
over future decades (2010 – 2050) with random hurricanes and various regimes of coral bleaching predicted by different 
climate change scenarios (aggressive mitigation/no mitigation of greenhouse gas emission to limit global warming). Model 
simulations predicted further declines in coral cover due to accelerated bleaching events, with a progressive loss of rugosity 
depending on the rate of carbonate bioerosion. Mitigating greenhouse gas emission significantly slowed down the decline in 
the quality of the reef habitat. Using a simple empirical relationship between reef rugosity and the number of fish species 
    Bozec, Y – M.  et al.    GCFI:65   (2013) Page 105 
 
per unit area (Luckhurst and Luckhurst 1978) the model 
allowed projecting the rate of biodiversity loss for both 
scenarios.  
Although preliminary, this model marks a significant 
step in our ability to model the dynamics of habitat 
structure on coral reefs. Further work is required to better 
describe the functional link between reef rugosity and fish 
assemblages, in order to provide reliable predictions of 
climate-induced changes in ecosystem functions (e.g., 
grazing intensity) and services (e.g., fisheries productivity). 
Such model developments are required to support the 
management of functionally complex reef habitats in the 
Caribbean. 
 
KEY WORDS: Topographic complexity, coral cover, 
mechanistic model, climate change, fish diversity 
LITERATURE CITED 
Alvarez-Filip, L., N.K. Dulvy, J.A. Gill, I.M. Côté, and A.R. Watkinson. 
2009. Flattening of Caribbean coral reefs: region-wide declines in 
architectural complexity. Proceedings of the Royal Society B: 
Biological Sciences 276:3019-3025. 
Luckhurst, B.E. and K. Luckhurst. 1978. Analysis of the influence of 
substrate variables on coral reef fish communities. Marine Biology 
49:317-323. 
Mumby, P.J. 2006. The impact of exploiting grazers (Scaridae) on the 
dynamics of Caribbean coral reefs. Ecological Applications 16:747-
769. 
Mumby, P.J., A.R. Harborne, J.D. Hedley, K. Zychualuk, and P. 
Blackwell. 2006. Revisiting the catastrophic die-off of the urchin 
Diadema antillarum on Caribbean coral reefs: fresh insights on 
resilience from a simulation model. Ecological Modelling 196:131-
148. 
 
 


Modelling the Response of Reef Rugosity and Fish Assemblages to Climate Change in the Caribbean

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Modelling the Response of Reef Rugosity and Fish Assemblages to Climate Change in the Caribbean

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