Gracilaria vermiculophylla in the Virginia Coastal Bays: Documenting the Distributionand Effects of a Non-Native Species

Abstract

Non-native species are of worldwide concern in both terrestrial and aquatic systems. Macroalgal introductions in coastal environments can have varied and often harmful effects, especially when surrounding habitats are altered by the invasion. Gracilaria vermiculophylla is a red macroalga that is native to East Asia and has been introduced to temperate estuaries around the world. It cannot be easily identified based on morphology alone, and is frequently mistaken for native congeners if genetic testing is not used. Mats of the macroalga can accumulate on subtidal and intertidal substrate within the Virginia coastal bays, USA and are held in place by tube decorating polychaetes on the order of months to years.The broad goals of this dissertation were to determine how widespread the G. vermiculophylla invasion was in the Virginia coastal bays and to document potential effects of G. vermiculophylla mats on biogeochemistry, trophic cascades, and on public health in the region. I found that the introduction was widespread in both subtidal and intertidal habitats, with higher intraspecific genetic richness and diversity than currently documented in other invasions. In addition, I found that intertidal sediment, marsh cordgrass, and mudflat invertebrates all incorporated nitrogen of G. vermiculophylla origin, which indicates that the macroalga is an important mediator of nutrient transfers in the system. Work on intertidal mudflats showed that the presence of G.ii vermiculophylla in this system, at moderate densities, could increase oxic-anoxic heterogeneity in the sediment and thus increase coupled nitrificationdenitrification. In addition, although G. vermiculophylla was associated with an overall increase in invertebrate biomass, shorebirds chose to forage on bare mudflats. Lastly, I found that G. vermiculophylla was a reservoir for the pathogenic bacteria, Vibrio parahaemolyticus and V. vulnificus which can cause gastroenteritis, severe wound infections, septicemia, and death in humans. In addition, oysters, sediment, and water collected in close proximity to mats of G. vermiculophylla had higher concentrations of both bacterial species when compared to samples collected on bare mudflats. Taken together, data collected within the Virginia coastal bays indicate that this widespread habitat modifier can have important effects on nitrogen availability, food web interactions, and shellfish sanitation.iii

Predicted Changes in the Biogeographical Range of Gracilaria vermiculophylla under Present and Future Climate Scenarios

“…The lack of monitoring programmes for the early detection of the presence of this species, or the difficulty of differentiating it from other native species such as Gracilaria asiatica (Zhang & B.M. Xia, 1985) or Gracilaria verrucosa ((Hudson) Papenfuss, 1950), may also explain its underestimation in non-native regions [5,12,14,21]. We suggest performing field assessments to check the presence of the target species in those areas where our SDMs forecasted its presence, but where it has not been recorded to date.…”

“…In these temperate regions, G. vermiculophylla is a perennial and foundation species that creates highly productive habitats and nursery grounds for fish and invertebrates, providing other ecological functions including CO 2 uptake and sequestration, organic carbon production and nutrient recycling [15][16][17][18][19]. Temperature, irradiance and salinity have been identified as the most important environmental variables controlling its physiological, growth and 2 of 16 reproductive responses [16,20,21]. Sea surface temperature (SST) is, aside from irradiation, one of the key factors that controls the germination and growth of macroalgae [22].…”