Viral infections of Ecklonia radiata
Ecklonia radiata the dominant habitat-forming seaweed in temperate Australia has experienced high rates of mortality in the last decades. Disappearance of this kelp forest would have serious consequences for the marine ecosystem. The causes of mortality are not yet understood but we hypothesise a combination of environmental stress and viral infection. We could demonstrate that disease symptoms such as discolouration and bleaching are widespread but patchy distributed around Australia, which does not correlate simply with latitudinal variation in water temperatures. Focussing on the Kelp populations along the highly urbanised coast of Sydney we observed a highly site-specific pattern in the frequency of disease symptoms in E. radiata populations. Photosynthetic activity of discoloured thalli was significantly reduced compared to co-occurring, healthy (dark brown) thalli. Moreover, we were able to demonstrate that discoloured tissue from Ecklonia radiata from multiple sites around Sydney were infected with a viral pathogen. Inoculation experiments in the laboratory with the extracted viruses of sick tissue resulted in infection of healthy tissue of Ecklonia radiata. The frequency of putative disease morphotypes, and the relative abundance of viruses in Ecklonia radiata around Sydney appear to be higher at sites that are impacted by untreated wastewater discharge.