Landscape edges shape dispersal and population structure of a migratory fish
Many freshwater organisms have a life-history stage that can disperse through seawater. This has obvious benefits for colonization and connectivity of fragmented sub-populations, but requires a physiologically challenging migration across a salinity boundary. We consider the role of landscape boundaries between freshwater and seawater habitats, and evaluate their potential effects on traits and developmental histories of larvae and juveniles (i.e., dispersing life-history stages) of an amphidromous fish, Galaxias maculatus. We sampled juvenile fish on their return to 20 rivers in New Zealand: 10 rivers had abrupt transitions to the sea (i.e., emptying to an open coastline); these were paired with 10 nearby rivers that had gradual transitions to the sea (i.e., emptying into estuarine embayments). We reconstructed individual dispersal histories using otolith microstructure, otolith microchemistry, and stable isotope analysis. We found that fish recruiting to embayment rivers had distinct dispersal and foraging histories, were slower growing, smaller in size, and older than fish recruiting to nearby non-embayment rivers. Our results indicate that landscape edges can affect dispersal capabilities of aquatic organisms, potentially leading to divergent life-history strategies (i.e., limited- versus widespread-dispersal). Patterns also suggest that dispersal potential among landscape boundaries can create heterogeneity in the traits of individuals, with implications for metapopulation dynamics.
KeywordsAmphidromy Dispersal Habitat edges Landscape ecology Seascape ecology
We acknowledge funding from the National Science Foundation (DBI 1306226) and Victoria University of Wellington; logistic support from Victoria University Coastal Ecology Laboratory; and research assistance from J. Bottcher, C. McDowall, C. Neilson, V. Wood, T. Bates, B. Focht, D. McNaughton, B. Moginie, D. Crossett, B. Focht, A. Kaemingk, A. Kilimnik and J. Brown. We thank C. Chizinski for statistical advice and three anonymous reviewers for improving this manuscript.
Author contribution statement
MK and JS jointly obtained funding, designed the study, supervised technicians, and drafted the paper with input from the other coauthors. MK analyzed the data. SS conducted LA-ICP-MS analysis. MK and SB conducted stable isotope analysis.
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