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Final Report: Saltwater Intrusion On The Gulf Coast: An Assessment Of The Interactions Of Salinity Stress, Genetic Diversity And Population Characteristics Of Fish Inhabiting Coastal Marshes
EPA Grant Number: R829420E03Title: Saltwater Intrusion On The Gulf Coast: An Assessment Of The Interactions Of Salinity Stress, Genetic Diversity And Population Characteristics Of Fish Inhabiting Coastal Marshes
Investigators: Leberg, Paul L. , Klerks, Paul L.
Institution: University of Louisiana at Lafayette
EPA Project Officer: Winner, Darrell
Project Period: June 10, 2002 through June 9, 2004 (Extended to June 9, 2006)
Project Amount: $133,410
RFA: EPSCoR (Experimental Program to Stimulate Competitive Research) (2001)
Research Category: EPSCoR (The Experimental Program to Stimulate Competitive Research)
Description:
Objective:A consequence of global climate change is the intrusion of saltwater into freshwater systems as a result of increased sea level. Coastal Louisiana is currently experiencing higher than expected salinities in traditionally freshwater marshes, waterways, and reservoirs. Most research has focused on plant communities; studies of the effects of saltwater intrusion on resident animal populations are usually limited to surveys documenting species replacement. There has been little investigation of effects of saltwater intrusion on the demography and genetic structure of wetland populations of fishes. We used this rapidly changing situation in Louisiana’s coastal marshes to understand how increasing salinity affects populations of resident fishes.
The objective of this research project was to examine how increasing salinity affects the ecology, demography, population structure, and genetic variation of these fishes. The model organism for this research will be the western mosquitofish (Gambusia affinis), a widespread and common predator that has been the subject of numerous studies on the effects of environmental stress on individual viability. We tested hypotheses that increasing salinity is influencing genetic variation through demographic bottlenecks and local adaptation. We also examined the hypothesis that marsh fragmentation, associated with sea-level rise, will increase genetic differentiation among populations, as well as extinctions of local populations.
Summary/Accomplishments (Outputs/Outcomes):Populations of mosquitofish differ in their salinity resistance; a population’s history of salinity exposure influences the future survival of the individuals challenged with stressful levels of salinity. This pattern is seen along two salinity gradients and does not appear to be a result of variation in life history traits. Furthermore, there is strong evidence that at least one resident marsh fish, G. affinis, is genetically adapted to local salinity conditions. This pattern was observed in each of two relatively isolated sets of populations; it is not clear if the variation in salinity resistance is due to the same genes in each set of populations. There are also large levels of variation in life history characteristics among populations of three resident marsh fishes (G. affinis, Poecilia latipinna, and Heterandria formosa) across the salinity gradient we examined. However, these patterns do not appear to be directly related to localized salinity conditions; we are in the process of determining if those in G. affinis have a genetic basis. Although populations have genetic differences in tolerance to high salinity levels, these differences have not resulted in strong differences in population performance in mesocosm studies evaluating responses to more chronic, lower levels of salinity. Microsatellite variation indicates significant levels of genetic differentiation among populations; the extent of this variation is still being quantified. Reduced gene flow might have made localized development of salinity resistance and variation in life history traits possible.
Abundances of fish species changed along the salinity gradient in expected ways; however, we found higher densities of resident marsh fishes than have been reported in many other studies. We think that this result was due to our sampling protocol, which involved sampling marsh at random rather than at points of access such as channels. We found that fragmented portions of the marsh had significantly lower nekton densities than unfragmented areas; however, there was a strong interaction with salinity. Fragmented and unfragmented marshes supported similar levels of nekton abundance in freshwater; however, fragmented brackish marshes supported much lower nekton numbers than unfragmented brackish marsh. These same patterns were observed for most common species of fish in our sample, but not for shrimp of the genus Paleomonetes. We also found that total nekton abundances were correlated positively with submerged aquatic vegetation (SAV) cover. Some species (G. affinis, P. latipinna, Cyprinodon variegatus, and Paleomonetes kadiakensis) showed strong interactions between SAV and position along the salinity gradient, such that vegetation was more important for maintaining high fish densities as salinity increased.
Conclusions:We now have evidence that resident marsh fishes have genetic adaptations for localized salinity conditions. This suggests the potential for future adaptation as sea levels rise. Continued adaptation will be most successful if salinities increase gradually. The test species apparently has sufficient physiological tolerance for populations with and without adaptation to salinity resistance to perform well at stressful, but non-lethal levels of salinity. The existence of adaptation to salinity tolerance will be most important in aiding survival during surges of high salinity, such as those associated with hurricanes.
Fragmentation is probably reducing gene flow among populations of resident marsh fishes, facilitating local adaptation; however, if isolated populations lose genetic variation through bottlenecks, the ability to adapt to changing coastal environments may be reduced. Such bottlenecks may become common as population abundances become suppressed in the high-salinity, fragmented marsh.
Fragmentation of coastal marshes, and the associated loss of submerged aquatic vegetation, is having an unforeseen effect on the species composition and abundance of the community of nekton. The dependence of resident marsh fishes on both emerged and submerged vegetative cover increases with salinity. Because fragmentation and vegetation loss often is associated with saltwater intrusion relative to sea level rise, this will lead to difficult management challenges. In the process of managing and restoring Louisiana’s coastal wetlands, maintenance of unfragmented marsh with both emergent and submerged vegetation is critical to retaining the historical functioning of the fish communities of Gulf Coast estuaries.
Journal Articles on this Report: 2 Displayed | Download in RIS Format
| Other project views: | All 15 publications | 3 publications in selected types | All 2 journal articles |
| Type | Citation | ||
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Leberg PL. Genetic approaches for estimating the effective size of populations. Journal of Wildlife Management, 2005. 69(4): 1385-1399. |
R829420E03 (2004) R829420E03 (Final) |
not available |
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Liebgold EB, Cabe PR, Jaeger RG, Leberg PL. Multiple paternity in a salamander with socially monogamous behavior. Molecular Ecology 2006;15(13):4153-4160. |
R829420E03 (Final) |
not available |
fish, gambusia, genetic diversity, marsh, saltwater intrusion, salinity tolerance, stress,
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Ecosystem Protection/Environmental Exposure & Risk, Air, Scientific Discipline, RFA, Oceanography, climate change, Ecology, Aquatic Ecosystems & Estuarine Research, Ecological Risk Assessment, Aquatic Ecosystem, Atmospheric Sciences, Ecology and Ecosystems, Environmental Monitoring, fisheries, fish communities, genetic diversity, Global Climate Change, habitat diversity, coastal ecosystems, fish habitat, wetlands, estuarine ecosystem, climatic influence, ecosystem impacts, sea level rise, aquatic ecosystems, coastal environments, environmental stress, coastal ecosystem, global change, salt water intrusion, aquatic ecology, ecosystem stress, ecosystem response, environmental stressors, global warming
Relevant Websites:
http://www.louisiana.edu/Departments/BIOL/leberg.html 
http://www.ucs.louisiana.edu/~pll6743/
Progress and Final Reports:
2002 Progress Report
2003 Progress Report
2004 Progress Report
Original Abstract