Pathogen inferred to have dispersed thousands of kilometres at sea, infecting multiple keystone kelp species

Abstract

Protistan pathogens have been found to infect populations of some large brown macroalgae. Infection could reduce the ability of macroalgae to withstand hydrodynamic pressures through weakening tissues and reducing flexibility. Widespread mortality of macroalgae if disease outbreaks were to occur could have important flow-on consequences for biodiversity and ecosystem function. Recent discoveries of the protistan pathogen Maullinia infecting the ecologically keystone southern bull kelp Durvillaea in Chile, Australia, and on Marion Island, raise the possibility that this pathogen is dispersing across ocean basins with buoyant hosts. To determine whether Maullinia also infects southern bull kelp in New Zealand, samples of gall-like tissue from Durvillaea antarctica, D. poha, and D. willana were collected from intertidal sites, and genetic analyses (sequencing of partial 18S rRNA) carried out. Maullinia infections were detected in all three species of Durvillaea. Phylogenetic analyses show a close relationship of New Zealand Maullinia to M. braseltonii previously detected in Chile and on Marion Island. Based on its genetic similarity to distant lineages and its presence on buoyant hosts that have been shown to drift long distances at seas, we infer that Maullinia has dispersed across the Southern Ocean through rafting of infected bull kelp. Understanding the capacity of pathogens to disperse across oceans is critical part of forecasting and managing ecosystem responses to environmental change.

Local endoreduplication of the host is a conserved process during Phytomyxea-host interaction

“…Brown algae are photosynthetic organisms and primary producer in the marine environment which are taxonomically unrelated to angiosperm plants, which makes comparative studies with this parasite compelling from an evolutionary and biological point of view. So far, no spore formation of M. ectocarpii has been documented microscopically, although there is persuasive evidence for the presence of the secondary, gall inducing stage on kelp sporophytes (Blake et al, 2017; Mabey et al, 2021). Another clue that M. ectocarpii can fulfil a full life cycle is the presence of resting spores in the closely related Maullinia braseltonii which commonly infects the bull kelp Durvillaea spp.…”