Galls found on a wild Laminaria digitata by YB. at the Atlantic/Clachan Bridge, Argyll, Scotland (56°19’02.7″N 5°35’00.2″W) on the 11 July 2017.

On this stipe, 3 pieces of tissues were harvested and each conserved in one tube of RNALater and in another tube of 4% PFA:

• On piece harvested on flattened area of the stipe (potentially without the pathogens)
• Two pieces harvested on two different galls

Comments:

• Pictures of the full algae would have been helpful in case of species identification doubt.
• Pictures of a healthy alga make the comparison and the symptoms description easier.
• A tissue sample of a healthy alga would have help for the microscopy and the DNA analysis.

Some material corresponding to all three areas harvested have been hand cuts and observed under a microscope.

All the tissues observed contain a filamentous brown algal endophyte, including the one harvested on flattened area of the stipe. As said before, a tissue sample of a healthy algae would have preferable.

Closer observation shows it has helicoid plastids and, most likely, pyrenoids.

The Laminaria digitata seems to be infected by a brown algal endophyte (ie. Ectocarpus, Laminariocolax, Laminarionema…). According to the scientific literature, the prevalence of the endophytic algae could be quite high in a population. It can cause a range of symptom: galls, distorted stipes, crippled lamina, dark spot on the lamina, warts on the stipe but for the majority of the kelps, the infection is asymptomatic.