Fine-Scale genotypic diversity in the seagrass Halodule wrightii from Oso Bay

Seagrasses are the only marine angiosperms in the world. They reproduce sexually and asexually through clonal growth. Seagrass beds are vital ecosystems that harbor the adult and larval stages of many marine animals, including fish, manatees, stingrays and many other vertebrates and invertebrates. Seagrass also play a vital role in carbon sequestration, protecting shorelines from wave energy, and maintaining the water quality of coastal bays. Seagrass beds around the world are declining at alarming rates, and conservation-related research is becoming increasingly important. Genetic variation in seagrass beds has been demonstrated to be positively correlated with productivity, resistance to, and recovery from environmental stress. While several studies have examined genetic diversity at fairly large (meter) scales, few have examined fine-scale (cm) genotypic diversity. Diversity at this scale could have important implications for biological and chemical processes such as pollination or toxin neutralization. This project focused on the seagrass Halodule wrightii, otherwise known as "shoal grass”, the most abundant species of seagrass on the Texas Gulf coast. Ninety six single rhizome fragments were collected from each of three, 60 x 90 cm quadrats placed in H. wrightii beds on the south side of Ward Island, Texas. Each sample was genotyped and genetic diversity estimates (genotypic richness, evenness, and architecture) were produced for each qaudrat. We found a fair amount of genotypic variation at this scale, that declined from east to west in the sampling region. We also found the presence of a very large clone that was present in all 3 quadrats. We conclude that H.wrightii has been present near Ward Island for at least a century, and that environmental and/or anthropogenic factors may be influencing H. wrightii reproduction in an, as yet, undetermined manner.