CREC · Coastal Research Network On Environmental Changes

Coastal Research Network On Environmental Changes

The major threats to ecosystem stability and ecological service delivery are global in scale, rendering them difficult to address through geographically constrained or single discipline approaches. The primary objective of CREC was to establish an international network of collaborators facilitated through a comprehensive exchange programme to allow a transnational, transdisciplinary approach to understanding the threats faced by coastal wetlands, specifically mangrove forests. This allowed us to examine the complex mechanisms behind regional and global responses of these ecosystems to the key environmental drivers of climate change and land use. This became possible across multiple scales of time (daily to evolutionary) and space (local to inter-continental). The programme was designed in 5 scientific and 1 administrative Work Packages to examine mangrove systems in the context of (i) the interactive effects of climate and land use, (ii) the effects of transient and non-equilibrium dynamics, (iii) the interaction of abiotic and biotic factors, (iv) feedback mechanisms among hierarchical levels within the system, and (v) feedback loops between environmental changes and biotic responses. This provided a hierarchical understanding of environmental change and biological responses from the individual to the community level. The ultimate aim was to identify the optimum level of process-detail to allow modelling and reliable predictions of mangrove responses under different scenarios. What follows is a synthesis of the deliverables for each Work Package (WP). WP 1 addressed ongoing environmental change and its consequences, focusing on mangroves themselves, initially establishing a mangrove reference database and herbarium (www.vliz.be/vmdcdata/mangroves). The results indicate that it is important to align remote or weather station climate data with in situ conditions and that climate forecasts do not predict range expansion for all species. Temperature and aridity set the range limits for the two most important mangrove genera, with these limits differing among species. Notably, aridity must be compensated for by higher tolerance to low temperatures. Although, climate data and distribution models predict species presence/absence effectively at the regional level, mangroves do not occupy their full biogeographic potential, suggesting a key role for dispersal. WP 2 concerned physiological and morphological response to environmental change. The use of advanced approaches involving micro CT scanning and 3D analysis helped to study the evolution of a vascular system capable of functioning under the extreme conditions experienced by mangroves. This evolution seems to be a convergent process in mangroves, and Avicennia spp. in particular, have a highly flexible hydraulic (vascular) system, possibly explaining their eurytopic character and wide biogeographical range. Likewise, terrestrialisation in crabs has been convergent. The effects of temperature have powerfully driven speciation and evolutionary trends, with differences in temperature tolerance dictating the vulnerability of tropical and sub-tropical species to long-term climate warming. The semi-terrestrial nature of equatorial populations of mangrove crabs renders them less vulnerable to climate change than marine species. Importantly, mangrove crabs show a high degree of thermal plasticity that is evident even at the embryonic stages so that ovigerous females are not limited by the thermal sensitivity of the embryos they carry. An additional, critical finding linked to crab terrestrialisation is that they profoundly enhance the capacity for carbon sequestration of mangroves through aeration of the soils. WP 3 addressed population level responses to environmental change of both plants and animals. The application of terrestrial forestry methods to mangrove systems proved valuable for this. Mangroves exhibit very plastic responses to environmental conditions, and changes in plant allometry have important higher population and community level consequences. Change in the populations of economically important mangrove species has direct implications for human use and will be influenced partly by changes in dispersal rates. In addition to water currents, these are influenced by the wind. The degree of influence depends on the morphology of species’ propagules. In the case of crabs, responses to environmental conditions reflect plasticity in physiology, rather than morphology. Temperature influences the vulnerability of egg/larval survival and female fecundity to climate change, with associated knock-on effects for the entire mangrove community. Differences between tropical (Kenya) and sub-tropical (South Africa) populations are especially strong for the early ontogentic stages. Modelling of these data indicates greater vulnerability to recruitment failure in the tropics. As for mangroves, crab recruitment reflects the effects of water flow, particularly tidal flux, that interact with habitat to produce complex patterns in time and space. WP 4 concerned community level responses to environmental change, particularly nutrient supply. Nutrient supply has direct effects on mangroves. In some places (Australia), but not others (Brazil), nutrient supply influences growth rates and leaf characteristics, with disruption of the nitrogen fixation system under conditions of high evaporation and salinisation. Consequently, additional nutrient supply through the effects of cyclones on estuarine discharge enhances mangrove growth in arid regions. The prediction that the frequency of cyclones will diminish in Australia has negative implications for mangrove ecosystems there. Although nutrient supply affects mangrove growth directly, it does not influence the effects of herbivory. Fringe mangroves are especially sensitivie to herbivory, which is closely linked to crab density. Although theory predicts that herbivory will be higher in the tropics, we found that the intensity of herbivory is sensitive to the life history of the dominant herbivore, rather than to latitude. WP 5 synthesised the overall results through modelling to allow forecasting of mangrove responses to alterations in abiotic conditions. The work focussed on the development and application of the BETTINA, KiWi and mesoFON models and successfully released individual-based models as open access resources. Six key ecosystem services provided by mangroves were identified (including coastal protection) for which no economic evaluations exist. Mangroves show strong interactions among individual plants, with the balance between competition and facilitation shifting across gradients of environmental harshness. For example, the models supported the hypothesis that the main driver of species dominance is nutrient availability. Human exploitation is a key driver of mangrove degradation globally, and particularly important are factors that relate to recovery from disturbance. These include abiotic factors such as hydrological conditions, but the interplay of legal and illegal harvesting is critical in Brazil, as illegal harvesting does not allow sufficient time for recovery. Overall, mangroves are universally important as providers of ecosystem services and are vulnerable to degradation in the face of over-exploitation. However, the results indicate a high degree of regional differentiation in their responses to environmental conditions and vulnerability to long-term environmental change. WP 6 focused on project management. The scientific findings were possible mainly because the project allowed an exceptionally high degree of collaboration and interaction of scientists from different disciplines, working in different parts of the world. Mobility of researchers and students through the secondments allowed considerable exchange of expertise and knowledge exchange. There were problems, however, in aligning predicted dates of secondments with the availability of students. A particular highlight was the organization of a workshop at the Meeting on Mangrove ecology, functioning and Management (MMM3) in Sri Lanka that drew mangrove experts world-wide to discuss a joint analysis of mangrove degradation trends based on FAO data.

Data: CORDIS, © European Union