Nekton Population and Community Responses to Habitat and Urbanization Effects in North Carolina Tidal Creeks.

RUDERSHAUSEN, PAUL JOSEPH. Nekton Population and Community Responses to Habitat and Urbanization Effects in North Carolina Tidal Creeks (Under the direction of Drs. Jeffrey A. Buckel and Joseph E. Hightower). The southeastern United States coastline is experiencing rapid human development. Recognizing potential impacts from an expanding human footprint, the U.S. Environmental Protection Agency and North Carolina Division of Marine Fisheries have called for more scientific information to understand landscape-level anthropogenic impacts to fishes and crustaceans in the state’s estuaries. I researched nekton community and population-level responses to habitat and anthropogenic effects in first-order tidal creeks in coastal North Carolina; it is these headwater systems that are most likely to show responses to anthropogenic impacts due to their proximity to land-based development. I found that creekwide nekton communities changed from those dominated by resident species in less impacted systems to those dominated by transient species in systems that had lost marsh due to instream development and associated increasing water depth. At small (within-creek) spatial scales the nekton community responded to fragmentation; sites with anthropogenically deepened waters and conversion of marsh habitat to armored shoreline had declines in the relative contribution of marsh residents and were dominated by transient species. The dominant resident fish species from community analyses, Fundulus heteroclitus, had a lower probability of moving to sites impacted by development. The use of passive integrated transponder (PIT) tags was investigated in Fundulus heteroclitus to determine whether these tags could be used to estimate demographics of creek populations of this species. PIT tags were successfully implanted in adult Fundulus heteroclitus and tagged individuals were resighted with custom-built autonomous detection gear that allowed tidally-mediated movement patterns to be determined and apparent survival to be estimated in a tidal creek. This work was followed with research using PIT tags as a tool across a gradient of habitat types and instream impacts to determine rates of apparent survival and densities of adult Fundulus heteroclitus in multiple tidal creeks. Modeling revealed that rates of apparent survival were similar across creeks and watersheds with different levels of development but that creek-wide densities were greater in creeks that retained greater percentages of marsh. Finally, rates of areal production of larval/juvenile Fundulus heteroclitus within salt marsh habitats were estimated across creeks with different creek-wide and watershed characteristics. The percentage of salt marsh across full high tide wetted areas of creeks and percent watershed imperviousness were not important explanatory factors of areal production within the marsh, indicating the ability of this species to maintain areal rates of production specifically within marsh habitats despite landscape-level alterations in tidal creeks in this region. Rates of larval/juvenile Fundulus heteroclitus production extrapolated to high tide wetted areas of creeks were positively related to adult abundances in September of each year of sampling, suggesting that increased larval/juvenile production is the likely mechanism for more adult Fundulus heteroclitus in creeks with higher creek-wide percentages of marsh. Taken overall, the results of this dissertation research suggest that loss of marsh, shoreline armoring, and increasing water depths – all common anthropogenic impacts to tidal creeks in the southeastern United States will alter nekton communities and decrease densities of a trophically dominant nekton species in these systems. Nekton Population and Community Responses to Habitat and Urbanization Effects in North Carolina Tidal Creeks by Paul Joseph Rudershausen A dissertation submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Fisheries, Wildlife, and Conservation Biology Raleigh, North Carolina 2017