Edge Effects and the Population Structure of Humboldt Bay, California, Eelgrass (Zostera marinaL.)

Abstract

The physical structure of a habitat (e.g., fragmentation) may affect the distribution of genetic diversity within a population, and genetic diversity may alter ecological function. This study investigates the population genetics of Humboldt Bay, California, eelgrass in light of the habitat's fragmented physical structure. Historical and ongoing dredging operations in the bay maintain channels between fragmented tidal mudflats that are inhabited by eelgrass. A sample of 469 individuals, from 11 discrete fragments, was genotyped using microsatellite analysis. Ramets were collected at multiple points located at the edge and in the interior of each fragment. The sampling scheme was designed to detect evidence of population structure within and between fragments, as well as between edge and interior bed positions. Genetic diversity is not shown to differ among fragments and is not consistent with widespread clonality. Heterozygosity levels indicate that Hardy-Weinberg equilibrium predominates across loci in most instances. Comparisons of edge and interior bed positions also reveal similarities between positions for the metrics described above. Results suggest efficient gene flow between fragments and between bed positions. Such findings, which indicate the unstructured nature of the population, can guide resource managers in making evolutionarily informed conservation decisions by discouraging assumptions of low genetic diversity and insignificant sexual reproduction.

The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

“…In a patch of Veronica anagallis-aquatica, the more exposed edge individuals presented smaller sizes than the sheltered ones, lower relative allocation to stems, higher allocation to roots, and reduced water content in roots and stems [107]. The comparisons between edge and interior vegetation in the eelgrass Zostera marina show that inbreeding and clonal dominance would be more likely to occur away from fragment edges, but with tidal cycles moderating differences that might otherwise occur between edge and interior positions in a bed [108].…”