The global seagrass virome: Building international collaborations in viral metagenomics through aquatic phytopathogen surveillance

Supported by the Mario Einaudi Center at Cornell University

Seagrasses are rooted angiosperms (flowering plants) which occur in shallow marine waters worldwide. Seagrasses perform important ecosystem services. They provide protection to juvenile fish and other marine animals, many of which are of fisheries importance (Bell et al. 1984). They stabilize coastal sediments and thereby provide buffering capacity against storms (Ward et al. 1984). They are also active sites of nitrogen removal since they sustain reducing sediment conditions which permit denitrification, and thereby enhance filtration of terrestrial runoff and anthropogenic nutrients (Hansen et al. 2000, Iizumi & Yamamuro 2000). Hence, factors affecting the health of seagrasses in coastal marine ecosystems are relevant to resource sustainability efforts (Abal & Dennison 1996).

Seagrasses face numerous threats from anthropogenic sources, including eutrophication-induced decreases in light availability (through sedimentation) (Abal & Dennison 1996, Orth et al. 2017), propeller scarring (Orth et al. 2017), epiphyte load as a consequence of nutrient enrichment (Roman et al. 2019), and disease (Wilson & Lotze 2019). The cause of most seagrass diseases, and their geographical extent and within-population effects are poorly resolved (Tarquinio et al. 2019).

“Seagrass wasting disease” describes a condition in which seagrasses lose their ability to photosynthesize as a consequence of tissue necrosis, followed by disintegration of lamina and eventual loss of above-sediment biomass and rhizobia (roots) (Robblee et al. 1991). The cause of most seagrass wasting is not known, however a candidate pathogen Labyrinthula zosterae was described in 1991 affecting seagrasses  in Florida Bay during an intense die-off (Muehlstein et al. 1991). Recently, three novel viruses have been described (Potexvirus (Van Bogaert et al. 2019) and two Amalgaviruses (Park et al. 2018)) in seagrasses, representing the first viruses ever described from any aquatic plant. These findings suggest that viruses may be common constituents of seagrass communities. However, their pathology and ultimate impact on populations (epidemiology) remains unstudied.

Seagrass die-offs disproportionately affect developing economies (Unsworth et al. 2019). While seagrasses occur worldwide, the effects of climate change and storms is most pronounced in coastal regions of tropical countries, where seagrasses buffer their effects. There is therefore a strong need to understand the diversity of potential pathogens in seagrass communities in these areas and in context of seagrass phylogeny.

The goals of this project are multifold. First, we will determine the diversity of viruses associated with several species of seagrasses at geographically disparate locations to determine their phylogeny. Because closely related viruses likely infect closely-related hosts, we will infer the potential for detected viruses to spread into new populations. Second, we will determine the regional distribution of seagrass viruses by performing quantitative analyses to determine the geographic and within-population scale of infection. Finally, we will examine the relationship between relative anthropogenic impact (qualitative) and viral load in seagrass tissues to determine if human-induced stress imparts changes in viral prevalence and load.