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

Elahe Parvizi,Abigail L. Mabey,Ceridwen I. Fraser

doi:10.1007/s00227-021-03853-8

Elahe Parvizi, Abigail L. Mabey + Show 1 more

Open Access

https://doi.org/10.1007/s00227-021-03853-8

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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.

Highlights

Pathogens can have a major effect on ecosystem processes, and can exercise controls on populations through reducing the biomass and abundance of species, influencing the phenotypes of hosts, and altering species interactions (Price et al 1986; Harvell et al 2002; Groner et al 2016; Fischhoff et al 2020)
Durvillaea poha, D. antarctica and D. willana were visually examined for signs of any pathogenic infection such as lesions or galls. 123 tissue samples from individual Durvillaea species were collected from infected kelp to test the presence of Maullinia via genetic analysis
The protistan pathogen Maullinia was confirmed from three bull kelp species in New Zealand: the buoyant D. antarctica and D. poha, and the

Summary

Introduction

Pathogens can have a major effect on ecosystem processes, and can exercise controls on populations through reducing the biomass and abundance of species, influencing the phenotypes of hosts, and altering species interactions (Price et al 1986; Harvell et al 2002; Groner et al 2016; Fischhoff et al 2020). Parasites and pathogens are common in macroalgae, and whilst not all diseases will go on to disrupt ecosystem processes (Harley et al 2012; Groner et al 2016), when foundational species such as macroalgae are disrupted, it can have disproportionate impacts which cascade through trophic levels and alter habitat functioning (Harvell et al 1999; Schiel 2006; Cohen et al 2018). Such impacts are of particular concern in marine ecosystems where high levels of connectedness can facilitate rapid spread of pathogens over large distances (McCallum et al 2003). Monitoring in combination with long-term data collection, including assessing disease prevalence, is essential to enable us to effectively respond to and manage disease outbreaks through understanding how host–pathogen interactions vary with climate

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Methodology

Results and discussion

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