3.3 Kelps – brown algae

The brown algae include many edible seaweeds, and a number of brown algae contains alginate that is extracted commercially and used in a large number of products. Cultivated kelp species including Saccharina spp. (formerly called Laminaria) and Undaria spp. are typically used for food while alginate are extracted from a wide variety of cheaper wild-harvested raw material.

The marine brown macroalga Saccharina latissima (sugar kelp) is the closest Atlantic relative of S. japonica, which dominates the Pacific Asian, particularly Chinese, seaweed industry. Although knowledge on the nature of Saccharina disease is scarce, the extensive Chinese farming reported many disease outbreaks. Table 1 indicates the most common diseases and their causes.

There is now significant interest in the commercial exploitation of S. latissima aquaculture in several European countries. Already, disease outbreaks have been reported at S. latissima European seaweed cultivation facilities and wild kelp populations, the etiology is unclear. The gaps in our knowledge and the emerging nature of the research is illustrated by this video from Miriam Bernard on a windy shoreline. She is a PhD student studying the defence and resistance of S. latissima against endophytic pathogens.

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Transcript: Video of Miriam Bernard

Hi everybody my name is Miriam and I work in the Biological Station of Roscoff as a PhD student. This is the pretty organism I work with, it is called Saccharina latissima or the Sugar Kelp and it is harvested and cultured as a food source. [A young woman stands on a pier by the sea holding up a large undulating brown seaweed frond about 1.5m in length]. This is what a healthy individual looks like, but unfortunately their have been disease outbreaks in former times, both in the wild populations and also in cultures. Then what happens is at the stipe, which is very straight and regular now, in infected plants it can be completely twisted [She holds the plant up to show the stipe or stem which in this example is straight]. Also their can be changes in the blade so there might be darks spots on the blade, and most importantly there might be changes in the biomass of infected plants. [She holds up the undulating/wavy blade which is brown with a sheen]. At this moment we think that the for this disease is a very small algae that lives inside of the big algae, and it looks like this, I hope you see it. [She removes a small clear petri dish from her pocket. It contains a clear liquid and in the liquid that are small but discernible brown spots. She points to these with her finger.]. The small brown dots that swim around in the water, and we think that this small algae might be change the growth of big algae. What I want to find out in my PhD is, is the small algae really the cause for the disease, and if so, what is the detailed mechanism of the infection, are their maybe any resistant plants. Or, are their other organisms that can help the big algae to cope with the infection

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Video of Miriam Bernard

Putative pathogens are endophytic filamentous algae that could affect kelp growth, and less well studied fungi, bacteria and viruses. For example the brown algal endophytes of the genera Laminariocolax and Laminarionema could be highly prevalent in European wild kelp populations and are currently studied. They presumably invade the seaweed stipe and frond, and in some instances could severely perturb morphogenesis.