Modelling coral reef fish larvae

Fish larvae are rare and fragile, which makes them particularly difficult to capture and study in situ. As a consequence, a flourishing field of numerical modelling opened, trying to predict the outcome of the dispersal phase.

Where To GoRather than trying to implement the very few details we have on in situ larval behaviour, we tackled the question of larval dispersal from the opposite special case: self-recruitment. Indeed, the real problem is explaining the unexpectedly the high self-recruitment rates measured from various observations. In addition, the mechanisms that enhance retention are general enough to be selected in various environments, as opposed to mechanisms that increase dispersal (e.g. swimming towards the birthplace is usually good, swimming away from it can be good or can be suicide depending on the configuration of the rest of the environment). This allows us, in turn, to resolve the problem at an evolutionary level and to build a model similar to those developed within the optimal foraging theory. Given an environment, we compute the decision, in terms of swimming and feeding, that optimises a biologically meaningful criterion, such as maximising survival or minimising energy expenditure.

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Such a model, in which behaviour is deduced from the environment, can clarify which factors influence most pelagic trajectories and, therefore, enable us to understand the mechanisms that drive self-recruitment vs. dispersal, what a purely descriptive study cannot.

I started this project during my Master in the Ichtyo-ecology team of the Mediterranean and Tropical Ecology laboratory of the EPHE and University of Perpignan. My advisors were Serge Planes, from this lab, and Michel de Lara from the CERMICS, a research group of the École Nationale des Ponts et Chaussées (ENPC). The basis of this model was elaborated very efficiently by Anselme LeVan, a student of the ENPC, during an internship from February 2002 to July 2002. The code, which is mostly Fortran 90 with some R scripts for running quick simulations and plotting, is kept as a Gitorious project.

Currently, our model represents a larva, born on an isolated island or promontory, which moves within a dynamic flow provided by a physical model (ROMS). The optimisation criterion is the minimisation of energy expenditure for swimming, because it can be considered as a trade-off with growth and survival, both during and after the pelagic phase. Technically, the choice of the optimal strategy is a dynamic optimisation problem which is solved by means of stochastic dynamic programming.

Downloads

  • Current code on Gitorious

  • Lett C, Ayata S, Huret M, Irisson J-O. Biophysical modelling to investigate the effects of climate change on marine populations dispersal and connectivity Progress in Oceanography, 87:106-112, 2010. [PDF]

  • Irisson, Chérubin, de Lara, Planes, 2009. Comportement larvaire et autorecrutement: Une approche de modélisation. Presentation, Symposium GLOBEC France, Paris [Slides]

  • Irisson, Chérubin, de Lara, Planes, 2009. Consequences of increased mobility and quicker development in warmer waters on the dispersal trajectories of fish larvae. Poster, Symposium GLOBEC France, Paris [Poster]

  • Irisson, Paris, Chérubin, de Lara, Planes, 2009. The importance of behaviour for self-recruitment: a modelling approach. Presentation, International Coral Reef Symposium, Fort Lauderdale, USA [Slides]

  • Irisson J-O, Leis J M, Paris C B, Browman H. Larval behaviour and settlement. In: Manual of Recommended Practices for Modelling Physical-Biological Interactions in Fish Early-Life History, North E, Gallego A, Petigas P (eds). ICES Cooperative Research Reports, Nº; 295, 2009 [PDF]

  • Irisson, Chérubin, Planes, 2008. Consequences of increased mobility and quicker development in warmer waters on the dispersal trajectories of fish larvae. Presentation, Ocean Sciences Meeting, Orlando, USA. Outstanding Student Presentation Award [Slides]

  • Paris, Srinivasan, Chérubin, Cowen, Irisson, Planes, 2006. Influence of biophysical processes on coral reef fish population connectivity inferred by modelling. Poster, Workshop on advancements in modelling physical-biological interactions in fish early-life history: recommended practices and future directions (WKAMF), Nantes, France. [Full size poster]

  • Irisson, de Lara, Planes, 2005. Lagrangian or not lagrangian?. Presentation, Lagrangian Analysis and Prediction of Coastal and Ocean Dynamics (LAPCOD) meeting 2005, Lerici, Italy. [Slides, Handouts]

  • Irisson J-O, LeVan A, de Lara M, Planes S. Strategies and trajectories of coral reef fish larvae optimizing self-recruitment. Journal of Theoretical Biology, Vol. 227, pp. 205-218, 2004 [PDF]

Contact

Laboratoire d'Océanographie de Villefranche

Station Zoologique, B.P. 28, Chemin du Lazaret, 06234 Villefranche-sur-Mer Cedex

irisson (at) normalesup.org
+33 (0)4 93 76 38 04

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