Abstract
Durvillaea antarctica (Fucales, Phaeophyceae) is a large kelp of high ecological and economic significance in the Southern Hemisphere. In natural beds along the central coast of Chile (Pacific Ocean), abnormal growth characterized by evident gall development and discolorations of the fronds/thallus was observed. Analysing these galls by light microscopy and scanning electron microscopy revealed the presence of endophytic eukaryotes showing typical characteristics for phytomyxean parasites. The parasite developed within enlarged cells of the subcortical tissue of the host. Multinucleate plasmodia developed into many, single resting spores. The affiliation of this parasite to the Phytomyxea (Rhizaria) was supported by 18S rDNA data, placing it within the Phagomyxida. Similar microorganisms were already reported once 23 years ago, indicating that these parasites are persistent and widespread in D. antarctica beds for long times. The symptoms caused by this parasite are discussed along with the ecological and economic consequences. Phytomyxean parasites may play an important role in the marine ecosystem, but they remain understudied in this environment. Our results demonstrate for the first time the presence of resting spores in Phagomyxida, an order in which resting spores were thought to be absent making this the first record of a phagomyxean parasite with a complete life cycle so far, challenging the existing taxonomic concepts within the Phytomyxea. The importance of the here described resting spores for the survival and ecology of the phagomyxid parasite will be discussed together with the impact this parasite may have on ‘the strongest seaweed of the world’, which is an important habitat forming and economic resource from the Southern Hemisphere.
Highlights
Durvillaea antarctica (Chamisso) Hariot is a large brown seaweed which belongs to the order Fucales (Phaeophyceae) [1]
Gametes in antheridia and oogonia, differentiated inside ovoid conceptacles that develop in the cortical zone with a small ostiole that opens to the surface (Fig. 2d) as described by Hoffmann and Santelices [3]
Phytomyxea are a group of obligate biotrophic parasites. They were recognized as protists when the group was first established, they were considered to be basal fungi for a long time [37]. These organisms were mostly referred to as ‘‘Plasmodiophorids’’ to avoid taxonomic placement, a name which is still commonly used for this group
Summary
Durvillaea antarctica (Chamisso) Hariot is a large brown seaweed which belongs to the order Fucales (Phaeophyceae) [1]. It has a subantarctic distribution limited to the Southern Hemisphere, South America, New Zealand and subantarctic islands [2,3]. This algal species plays an important role in the occupation of habitat and the structuring of coastal communities. It frequently dominates the intertidal and shallow subtidal flora in regions with a stable, rocky substratum that is exposed to wave force [4]. Its long, floating fronds can reach a length of more than 15 m [8], and its holdfast by itself constitutes a temporal or permanent habitat for a rather large number of different species of invertebrates by giving them shelter, by conforming spawning and habitat substrates, and by minimizing wave and predation pressure [9]
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