Are microbes to blame for the loss of underwater seaweed forests?

[Global] Dense aggregations of tall, brown seaweeds are commonly found along temperate coastlines. These underwater kelp forests thrive in cool, nutrient-rich waters and are often teeming with life because their large, tree-like bodies form nooks and crannies for a wide variety of sea creatures to hide in. However, as the oceans warm, nutrients become harder to come by and the kelps begin to deteriorate, taking the habitat they create with them. And now, a new study shows that the microscopic life forms that live on the kelp (“microbes”) may also be sensitive to changing ocean conditions, leaving the kelps vulnerable to infections and diseases.

“Kelp forests are sensitive to warming because kelps are cold water species – they evolved to live in polar to temperate waters. Once kelps get above that temperature range, they can’t function normally,” says Dr. Christina Bonsell, a research associate at the University of Texas Marine Science Institute.

In a month-long laboratory experiment, the researchers exposed young kelps that were 12 – 24 inches tall to increased temperatures and acidity representative of ocean conditions in the year 2100. Within one week, the microbial communities on the kelp began to change and soon the kelps’ tissues began to blister and bleach. Interestingly, the microbes associated with damaged kelps differed from those that lived on healthy kelps. However, as the kelps continued to degrade in response to changes in temperature and seawater chemistry during the second week of the experiment, the microbes exposed to both warming and increasing acidity began to revert back to a community that resembled those on the healthy kelps.

“Some symbiotic relationships between kelps and their associated microbiomes, as well as for other organisms, including humans, are essential and provide a stable balance, ” says Dr. Raquel Peixoto, professor of microbiology at the Federal University of Rio de Janeiro in Brazil and  visiting professor at the University of California, Davis. “The microbiome can benefit the kelp, for example, by producing vitamins, enhancing nutrient uptake or degradation, avoiding colonization by pathogens … and toxic compounds. If the  microbial community is affected … the symbiotic relationships, and consequently, the organism’s health, are also affected.”


Photo: Kelp forest at A-Frame, Simon’s Town, Cape Peninsula.PETER SOUTHWOOD | WIKIMEDIA COMMONS

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