Functional, Phylogenetic and Host-Geographic Signatures of Labyrinthula spp. Provide for Putative Species Delimitation and a Global-Scale View of Seagrass Wasting Disease

Abstract

Seagrass meadows form ecologically and economically valuable coastal habitat on every continental margin except the Antarctic, but their areal extent is declining by approximately 2-5 % per year. Seagrass wasting disease is a contributing factor in these declines, with the protist Labyrinthula identified as the etiologic agent. To help elucidate the role of Labyrinthula spp. in global seagrass declines, we surveyed roughly one fourth of all seagrass species to identify Labyrinthula diversity at the strain and/or species level, combining results from culturing methods and two common nuclear DNA markers: the ITS and 18S regions of the ribosomal RNA gene complex. After assaying a subset of the resulting isolates (of which 170 were newly sequenced), we produced a cladogenic context for putative seagrasspathogenic versus non-pathogenic Labyrinthula while also defining host and geographic ranges. Assays also suggest that pathogenicity is consistently high (when present; and, even when comparing susceptibility of US East-versus West Coast Zostera marina hosts) while virulence is variable, that some isolate-host combinations have the potential for host cross-infection, and that several modes of transmission can be effective. Taken together, these data provide additional means for delimiting putative species of Labyrinthula, suggesting at least five seagrass-pathogenic and perhaps ten or more non-pathogenic marine Bspecies^, yielding a working definition for ecologists and epidemiologists attempting to reconcile the sundry data related to seagrass wasting disease.

Oysters and Eelgrass: Potential Partners in a High pCO2 Ocean

“…EWD outbreaks in the northwest Atlantic in the 1980s were associated with eelgrass population declines (Short et al 1987). Currently, in the Northeast Pacific, infectious strains of LZ have been isolated from eelgrass blades exhibiting signs of EWD, indicating a potential role in local eelgrass declines (Groner et al 2014, 2016, Martin et al 2016). The influence of increased pCO 2 on the resilience of eelgrass to EWD or infection by LZ is unknown, although OA is a growing issue in this area (Feely et al 2010).…”

The First Isolation and Characterisation of the Protist Labyrinthula sp. in Southeastern Australia

“…Not all Labyrinthula isolates are pathogenic and some live as saprobic decomposers (Martin et al. ). Still, the cause of opportunistic pathogenicity is uncertain.…”

“…) and/or (ii) linked to species lineages whereby some species are more virulent than others (Martin et al. ).…”

“…In the past 50 yr, just five isolates have been cultured from Australian (Martin et al. ; Vergeer and Den Hartog ) and New Zealand (Armiger ) seagrasses. In these efforts, the genus was primarily described through morphological observations of cultured isolates, namely cell size and the growth pattern of the colony.…”

“…More recently, genetic sequencing using 18S and internal transcribed spacer (ITS) markers have improved our knowledge of Labyrinthula globally (Bockelmann et al ; Martin et al. ), and has included isolations of a potentially pathogenic strain from Queensland in Australia (Bockelmann et al ; Martin et al. ).…”