The Role Of Disturbance In The Genotypic And Morphological Diversity Of Halodule Wrightii

Seagrasses are important foundation species in coastal ecosystems. Genetic
diversity of seagrasses can influence a number of ecological factors including, but not
limited to, disturbance resistance and resilience. Seagrasses in the Indian River Lagoon
(IRL), Florida are considered to be highly disturbed due to frequent events, like algal
blooms, that impair water quality, reducing available light for seagrass growth. Halodule
wrightii is a dominant seagrass throughout the IRL, but its genetic diversity has only been
quantified in a few Gulf of Mexico and Florida Bay populations and little is known about
its potential ecological consequences. I quantified the genetic variation of H. wrightii
using microsatellite markers in the southern IRL to determine: (i) how disturbance history
influenced genetic diversity, (ii) if morphology of clones was, in part, genetically
controlled and related to disturbance history, and (iii) if genotypes showed phenotypic
plasticity in response to disturbances. In the IRL, H. wrightii populations exhibited moderate genetic diversity that varied with disturbance history. The disturbance history
of a population was classified by the variance in the percent occurrence of H. wrightii
over a 16-year period. Genotypic richness and clonal diversity of H. wrightii increased
with increasing disturbance histories. Other genetic diversity measures (e.g., allelic
richness, observed heterozygosity) did not change with disturbance history. These
findings suggest that impacts to seagrass coverage over time can change the genotypic
composition of populations. When different genotypes of H. wrightii were grown in a
common garden, differences in leaf characteristics among genotypes provided evidence
that morphological trait variation is, in part, explained by genetic variance. The
disturbance history of genotypes did not directly affect morphological traits. However,
significant genotype x site (within disturbance history) interactions found greater
variation in shoot density and below ground traits of H. wrightii genotypes from sites of
intermediate disturbance history. Traits of H. wrightii were shown to be phenotypically
plastic. Significant genotype x environment interactions for shoot density and height
demonstrated that genotypes responded differently by increasing, decreasing, and not
changing sizes in response to light reduction. Genetic diversity of H. wrightii has strong
implications for ecological function in coastal communities.