Long-term effects of environmental changes on the nekton biodiversity and the functioning of tropical estuarie

Anthropogenic impacts are deeply modifying – sometimes irreversibly - environments and geochemical fluxes. Estuarine and coastal ecosystems, which are among the most productive systems on Earth, are under increasing pressure due to drastic changes in land use of watersheds, acceleration of coastal urbanisation, sea rise and global warming. Among those ecosystems, tropical estuaries are marked by a high biodiversity and provide ecosystem services of high value (protein supply through fishing, water filtration, nursery habitats for juveniles) while they are severely impacted by mangrove deforestation, over fishing, aquaculture and increasing rates of sediment loading. Tropical estuarine ecosystems also yield a high diversity of habitats such as mangrove swamps, seagrasses beds, muddy or sandy sediments.

These different habitats and their associated communities are not expected to respond in the same way when facing disturbances. For instance, many studies have reported seagrass loss following drastic environmental changes induced by human influence such as eutrophication. In turn, these modifications in the composition of these vegetated habitats may alter their quality for associated fish and invertebrates with, as a consequence, a loss of some ecosystem functions and a decrease in secondary productivity. In these coastal ecosystems, the nekton that is dominated by fish plays an important role in nutrient fluxes, both along the trophic level and through space with migrations. Thus, we urgently need to determine the factors (i) that maintain or threaten the biodiversity of nektonic communities, (ii) that influence fish growth, (iii) that modify fish migration patterns, and (iv) that induce shifts in trophic structures and ecosystem functioning.

We focus on the Terminos tropical estuary (Mexico) coupled with the coastal Campeche Sound where historical data are available (1980, i.e. 30 years ago) on both biotic (nekton, fish) and abiotic factors (salinity, temperature, depth etc...). The Terminos lagoon, which is an exceptional case study regarding the collection of old data, is considered an archetypal tropical estuary under increasing pressure, which we can exploit to address our four issues, in particular by performing a new sampling campaign during the project to follow the dynamic since 1980.

The originality of our project lies in the linking, into a single framework, of long term observations, organismal biology, and modelling. Moreover we believe that the project is innovative and original because: - Previous studies have provided a solid foundation of empirical evidence showing phase-shifts in coastal ecosystem functioning after environmental changes, yet the modelling of such relationships is still lacking in marine science. Modelling such complex systems will be very original and innovative. - We still lack large scale studies on the relationship between disturbance, ecosystem functioning and community structure. To our knowledge this will be the first time that such relationships will be investigated and modelled at large temporal and spatial scales. - The outputs from these combined analyses are likely to bring sufficient knowledge to contribute towards a better coastal ecosystem management.

Objectives

Our project aims at a deeper understanding of the causes and consequences of modifications in the biotic structure of nekton assemblages within a contexte of environmental changes (local and global influences). We focus on the Terminos tropical estuary (Mexico) coupled with the coastal Campeche Sound where historical data are available (1980, i.e. 30 years ago) on both biotic (nekton, fish) and abiotic factors (salinity, temperature, depth etc...). The Terminos lagoon, which is an exceptional case study regarding the collection of old data, is considered an archetypal tropical estuary under increasing pressure, which we can exploit to address our four issues, in particular by performing a new sampling campaign during the project to follow the dynamic since 1980.

Objective 1: In the present project, we will investigate how the various facets of fish biodiversity have been affected by abiotic shifts and habitat degradation in the Terminos ecosystem over the last 30 years.

Objective 2: to assess growth changes in fish population 30 apart. A better knowledge on fish growth differences will serve the purpose explaining changes in fish abundances over time and implementing the modeling phase.

Objective 3: We aim to quantify fish migration patterns between the Terminos lagoon and the Sea and to detect changes that have occurred over the last 30 years. A better knowledge of migration patterns will serve to explain changes in fish biodiversity and to implement the modeling phase.

Objective 4: The main objective of this working group is to explore the scaling of the effects of changes in functional biodiversity in terms of structural and functional changes at the ecosystem level, as well as in its temporal and spatial dynamics, including the perspective of climate change. The originality of our project lies in the linking, into a single framework, of long term observations, organismal biology, and modelling.

Partners

The 4 partners have well-established international expertise in Marine Ecology, Estuarine Ecosystems and Trophic Modeling. The association of scientists from various laboratories for this project is fully justified. Not only will research unit diversity allow access to all the equipment, facilities and analytical systems necessary for its completion, but such a multidisciplinary study also involves many competencies that cannot easily be found within the same laboratory.

Partner 1: ECOLAG [Montpellier, France]

The ECOLAG laboratory is a CNRS-University Montpellier 2- IFREMER-IRD joint research unit (UMR N° 5119) which focuses its research activities on the study of “the effects of local and global changes linked to human activities on lagoons and marine coastal ecosystems”, in the Mediterranean and tropical areas. It implies an integrative approach combining, at various scales (local, global), the characterization of all main biological, physical and chemical components, the study of their interactions and the related functions using field experiments with mesocosms, models and quantitative tools for scenarios analysis and prediction.

Partner 2: LEMAR [Brest, France]

The team of the Institut de Recherche pour le Développement (IRD) in Brest was established between 2001 and 2007 in the Laboratoire de Sclérochronologie des Animaux Aquatiques (LASAA). LASAA is a French laboratory set up in June 1993 by two national research institutes, IFREMER and IRD in order to develop technical and scientific concepts concerning research in sclerochronology (estimation of time from the growth marks recorded and preserved in calcified tissues, recording of environmental parameters in these archives, development of new technologies in imaging and chemical analysis).

Partner 3: EPOMEX [Campeche, Mexico]

EPOMEX is a research center belonging to the Autonomous University of Campeche was created in 1990 to address research problems related to coastal and marine zone of the Gulf of Mexico in five priority areas: ecology and coastal zone management, tropical fish, pollution and environmental impact, and coastal aquaculture. EPOMEX supports the government of the state of Campeche in: land management, coastal zone management, biological, ecological and fisheries resources, problems of pollution impacts and environment, pathobiology, ecotoxicology, bacteriology and GIS, all this in the coastal and marine zones.

Partner 4: CICIMAR [La Paz, Mexico]

The Interdisciplinary Center of Marine Science from the National Polytechnic Institute (CICIMAR) has a strong experience on fisheries science which concentrates most of fisheries scientist in the country. Some key problems as been faced are aimed to stock assessment, population biology, fisheries management, ecosystem based management, interacting with the National Institute of Fisheries, industry, NGOs, fishers, governmental entities aimed to conservation, and advising on conflictive situations between conservation and fishing in natural reserves. Other areas of the Marine Sciences are developed with groups aimed to biodiversity, environmental impact, marine ecology, experimental biology, and different branches of the oceanography.