Isolated salt marsh colonization by a resident species, mummichog (Fundulus heteroclitus), and a transient species, pinfish (Lagodon rhomboides)

•Mummichog occupied depopulated marshes within weeks through adult colonization.•Pinfish occupied depopulated marshes within months via young-of-year colonization.•Adult colonization maintains mummichog large-scale (geographic) distribution.•YOY recruitment maintains small-scale (local) mummichog populations.•YOY recruitment and colonization maintain pinfish geographic and local populations.

The potential for species to populate habitat patches is directly influenced by dispersal and colonization abilities. To test the dispersal and colonization capabilities of a resident, mummichog (Fundulus heteroclitus), and a transient, pinfish (Lagodon rhomboides), marsh species, isolated-island marsh sites were used for removal and colonization assessments, while a nearby non-removal site was used to concurrently monitor temporal catch variability. F. heteroclitus and L. rhomboides were removed from island marshes using baited minnow traps during mid-fall 2004 (after F. heteroclitus spring/summer spawn, and prior to L. rhomboides winter recruitment), then monitored for colonization through the peak F. heteroclitus spawning season the following year (July 2005). Significant abundance reductions occurred for F. heteroclitus and L. rhomboides due to removal efforts, and for L. rhomboides due to temperature-dependent offshore migration. F. heteroclitus and L. rhomboides were capable of seasonally colonizing marsh sites separated by > 800 m of open water, which was twice the previously documented distance for F. heteroclitus movement within marsh habitats. Results from size-class analysis indicated that F. heteroclitus populated sites via adult colonization from nearby marshes within weeks to months of removal. L. rhomboides site colonization occurred by young-of-year (YOY) recruitment and was documented within months of removal efforts, when YOY attained sufficient size for gear collection. Low population contribution by F. heteroclitus YOY to island compared to mainland type marsh indicated that island marshes were primarily sustained by immigrants, which colonized during late fall and winter, while YOY production sustained the population at the mainland marsh. Island marshes acted as sinks for estuarine F. heteroclitus populations. F. heteroclitus population characteristics were determined during: (1) the spring/summer spawn and recruitment, and (2) the late fall/winter dispersal-colonization by adult F. heteroclitus. Further, the F. heteroclitus dispersal-colonization phase maintains the species' large-scale (geographic) distribution, while the spawn-recruitment phase maintains the small-scale (local) populations. L. rhomboides recruitment and dispersal-colonization occur simultaneously during late fall/winter when pulsed dispersal-colonization by recruits maintains geographic and local populations.