Laboratory: Ifremer Guyane, Fisheries Biodiversity Unit, UMSR LEEISA (University of Guyane-CNRS-Ifremer) Supervisors: Fabian Blanchard (research director) and Vincent Vallée (PhD student)

The application forms (CV + motivation letter in French or English) have to be sent to: [email protected] and [email protected]

Financements FEDER et Ifremer

Context and subject:

For more than two decades, describing and understanding the spatio-temporal dynamics of fish communities has been subject to increasing attention from scientists and fisheries managers. Such dynamics are crucial for ecosystem functioning and productivity which provide goods and ecosystem services. Changes in fish community assemblages could actually be explained by fishing and climate change (Poulard and Blanchard, 2005; Travers et al., 2007; Auber et al., 2015).

The impact of fishing and climate change on fish communities have been the subject of studies for several years (Myers and Worm, 2003; Auber et al., 2015). Both have undisputable effects on species’ ecology and functions but are often difficult to disentangle insofar as two forcing variables could have the same effects on an indicator (Auber et al., 2015; Bell et al., 2015). Thus, monitoring the ecosystem state from multi-specific indicators based on a particular impact factor remains difficult. Moreover, these works focused mainly on temperate and boreal ecosystems. If temperate ecosystems can be colonized by subtropical species in a global warming context, the adaptation capacity of species to warmer waters than those currently observed in tropical ecosystems still remains unknown. Therefore, questions arise about the existence of species that are able to colonize the tropics when warming. Sub-tropical species occurring in tropical regions at the warm limit of their range could be disfavoured in a warming period and can finally lead to a biodiversity loss.

It is therefore proposed (1) to describe trends of environmental parameters (Sea Surface Temperature, turbidity, salinity…) of the French Guiana continental shelf off waters from 1990 to 2017 and then (2) to analyze the ground fish communities’ spatio-temporal structure based on species’ thermal affinities and the significant warming since the early nineties using taxonomic and functional diversity indices.

Understanding diverse processes that can shape biological communities’ structure and functioning under multiple disturbances is a major challenge in ecology. Traditionally, disturbance impacts were assessed by analysing taxonomic community structures. In recent years, progress has been made in the application of species traits to assess the functional diversity of communities (Mason et al., 2005; Bremner, 2005; Bellwood et al., 2006; Villéger et al., 2010). A widely adopted definition of functional diversity is “the value and the range of those species and organismal traits that influence ecosystem functioning” (Tilman, 2001).

Today, the functional approach is still not widely used but has been shown to be more effective and sensitive than the use of traditional methods alone (Mouillot et al., 2006; Mouillot et al., 2013) which are only based on taxonomic community structures. Functional diversity provides a complementary approach to taxonomic-based methods when investigating disturbance impacts as fishing and climate change. However, if a growing number of studies focuses on fish communities’ functional responses to environmental changes and fishing on temperate ecosystems, such studies are scarcer on tropical ones.

This work will be based on data sets compiled from 11 biological surveys conducted since 1993 to 2017 on 33 to 100 stations following the same sampling protocol using a bottom shrimp trawl between 10 and 60 m depth. The trait-based approach has been chosen to assess functional diversity and functional traits have already been gathered. The aim is to select and compute taxonomic and functional indices that provide the best results to describe changes in communities’ structure.

Profile required: The student must have interest for fisheries sciences and community ecology (assembly rules and functional diversity). Knowledge in multivariate analysis and R programming language are also needed.

References:
Auber, A., Travers-Trolet, M., Villanueva, M.C., Ernande, B., 2015. Regime Shift in an Exploited Fish Community Related to Natural Climate Oscillations. Plos One, 10(7), e0129883. doi:10.1371/journal.pone.012988
Bell, R.J., Richardson, D.E., Hare, J.A., Lynch, P.D., Fratantoni, P.S. 2015. Disentangling the effects of climate, abundance, and size on the distribution of marine fish: an example based on four stocks from the Northeast US shelf. ICES Journal of Marine Science, 72(5): 1311-1322.
Bellwood, D.R., Wainwright, P.C., Fulton, C.J., Hoey, A.S., 2006. Functional versatility supports coral reef biodiversity. Proceedings of the Royal Society B, 273:101-107.
Bremner, J., 2005. Assessing ecological functioning in marine benthic communities. Ph.D. Thesis University of Newcastle, 211pp.
Mason, N.W.H., Mouillot, D., Lee, W.G., Wilson, J.B., 2005. Functional richness, functional evenness and functional divergence: the primary components of functional diversity. Oikos, 111:112-118.
Mouillot, D., et al., 2006, a. Alternatives to taxonomic-based approaches to assess changes in transitional water communities. Aquatic Conserv Mar. Freshw. Ecosyst., 16: 469-482.
Myers, R.A., Worm, B. 2003. Rapid worldwide depletion of predatory fish communities. Nature, 423: 280-283.
Poulard, J-C., Blanchard, F., 2005. The impact of climate change on the fish community structure of the eastern continental shelf of the Bay of Biscay. ICES Journal of Marine Science, 62: 1436-1443.
Travers, M., Shin, Y.J., Jennings, S., Cury, P., 2007. Towards end-to-end models for investigating the effects of climate and fishing in marine ecosystems. Progress in Oceanography, 75(4): 751-770.
Villéger, S., Mason, N.W.H., Mouillot, D., 2008. New multidimensional functional diversity indices for a multifaceted framework in functional ecology. Ecology, 89, 2290-2301.
Villéger, S., Ramos Miranda, J., Flores Hernandez, D., Mouillot, D., 2010. Contrasting changes in taxonomic vs. functional diversity of tropical fish communities after habitat degradation. Ecological Applications, 20: 1512-1522.

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