Linking Historical Changes in Salt‐Marsh Coverage to Lost Production of a Nektonic Bioindicator

Abstract

Development reduces the amount of secondary biological production in coastal estuaries. However, the magnitude of this reduction remains largely unknown. We are not aware of studies that have quantified lost secondary biological production in estuaries as a result of interdecadal coastal development of salt-marsh habitats. Our objective was to demonstrate a technique that combined historical imagery, GIS, and secondary production estimates to quantify the magnitude of lost areal production arising from the development of tidal creeks. We estimated lost production of a dominant salt-marsh fish Mummichog Fundulus heteroclitus in Spooners and Pelletier creeks, two second-order tidal systems in coastal North Carolina. We georeferenced historical (1939) aerial imagery, digitized low-tide and high-tide features in historical and contemporary (2019) imagery, and compared the intertidal vegetated area of each creek between periods. The lost intertidal area was then multiplied by creek-specific published rates of areal production of larval and juvenile age-0 Mummichog in salt-marsh cordgrass Spartina alterniflora habitats. There was a loss of intertidal area and intertidal/subtidal vegetated edge of 72% and 54%, respectively, in Spooners Creek, and 47% and 4%, respectively, in Pelletier Creek. Losses of intertidal area over the last~80 years translated into estimated annual losses of 44 and 8 kg of dry weight production (~695,000 and 186,500 individuals) for a single cohort in Spooners and Pelletier creeks, respectively. These estimates represent minimum losses, as some in-stream development was already visible in the historic imagery and a single cohort's production was used (not multiple cohorts). We encourage other researchers to use historic imagery to determine changes in aquatic habitats and link losses (or gains) in these habitats to the productivity metrics of important fishes.