Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Christopher J Patrick

Committee Member

Mary C Fabrizio

Committee Member

John M Hoenig

Committee Member

James E Skelton


Historically, invertebrates have been significantly underrepresented in conservation efforts despite still experiencing extinction and threats to diversity. Gaps in our understanding of abundance and distributions for rare or cryptic freshwater species may contribute to a lack of necessary protections for these potentially threatened species. This problem is of particular consequence in coastal plain rivers which are critically under-studied systems, have an extensive history of anthropogenic impacts. Coastal plain freshwater environments are important corridors of ocean to freshwater connectivity. Disturbances or degradation of this corridor could have severe impacts on both permanent and migrant residents of the coastal plain. Texas Gulf coast plain is home to a number of decapods, such as crayfish species that are considered species of greatest conservation need (SGCN) by the USGS but suffer from a lack of clear distribution data. The gulf coastal plain of Texas is also home to the migratory caridean shrimp genus Macrobrachium, that were once common throughout Texas rivers, but have become increasingly rare. Habitat fragmentation caused by dams could be to blame for reductions in abundance and range contractions of the migratory Macrobrachium. In this project we produced species distribution models (SDMs) using random forest (RF) algorithms for crayfish species (n = 24) found in the Texas gulf coast prairies and marshes ecoregion (Ecoregion 34). We also conducted assessments of the current spatial range of Macrobrachium species in Texas by comparing current (post-1987) to historic (pre-1987) observations to determine changes in spatial distribution over time. In addition, we determined the effects of anthropogenic factors, such as dams and land-use, on Macrobrachium presence and persistence using generalized linear mixed effect models (GLMM) and produced SDMs using random forest for each species (n = 3). We found that a steep precipitation gradient in the Texas Gulf coastal plain likely drives distributional patterns of crayfish in the region. Land-use variables and dam variables were less important for driving crayfish distributions. For Macrobrachium we found all three species experienced severe reductions in range with dams as the most important anthropogenic factor predicting Macrobrachium presence and persistence. While dams negatively impacted all species of Macrobrachium, the largest species was able to circumvent smaller, older dams. With an improved understanding of current distributions and association of environmental and anthropogenic factors, an assessment of the conservation status of decapods is possible for the Gulf coast plain. In addition, our study improves our understanding of Macrobrachium range contractions and possible measures we can take to reduce anthropogenic impacts on the genus.




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