Deep corals off the coast of Hawaii, represent unique habitats, called mesophotic coral ecosystems. After reading a recent publication, these systems have become even more intriguing, as I learned that these low-light reefs between 40-130 meters below the surface contain a much wider diversity of fungi than we previously thought. Additionally, after sampling algal species for the presence of fungi, the marine fungi identified were compared to fungi living in terrestrial ecosystems. Quite amazingly, there was overlap, showing that some fungal species live both in these deep coral ecosystems, as well as the forest floor above the surface of the sea. This scientific survey not only shows the complexity of life underwater, but the extreme adaptability fungi possess.
The position of this mesophotic coral ecosystem. Wainwright et al. 2017.
Benjamin Wainwright and his team wanted to better understand what species make up these unique deep coral ecosystems. As ocean temperatures rise and increase in acidity, coral bleaching events are on the rise. It is possible that these ecosystems will be wiped out within a matter of decades so we should learn what we can from these unique habitats before they disappear. I’m not trying to be pessimistic here, but it would be a disservice to you if were to exclaim that ‘everything will be alright, and our natural communities will rebound.’ Realizing the near ephemeral state of our planet’s corals, Wainwright and his team set off to learn about these marine communities.
Using a state of the art submarine called Pices V, these researches set off to these mesophotic habitats to collect samples of microalgae and coral. They streamlined their study by focusing on the four ecologically dominant organisms present. After collecting multiple samples, tissue was stored and brought to the surface where it was then analyzed genetically. Out of all these genetic data, they isolated 147 fungal operational taxonomic units (OTUs)! Yes, you read that correctly. A diverse array of fungi is not just living in these amazing marine ecosystems but thriving.
Different species dominate different depths of mesophotic coral ecosystems. Sherman et al. 2010.
Even more interesting, is that when these fungal OTUs were compared to the genetic bank of the terrestrial ecosystems above, these researchers found that 39 of the 147 OTUs are also found living as plant epiphytes. How can the same organism exist on an algal counterpart in a mesophotic coral ecosystem, and on a higher plant leaf from the forest floor above? If this doesn’t show the adaptability fungi possess, then I don’t know what will. Like us, these fungi require oxygen and carbohydrates to survive. Even though only 10-1% of the sunlight is reaching these marine ecosystems, is it enough to allow photosynthesis to occur. As these organisms synthesize sugars by combining nutrients like phosphorus and nitrogen with the scant sunlight available, as a byproduct, oxygen is released.
The algae Microdictyon umbilicatum being sampled. Wainwright et al. 2017.
This byproduct of photosynthesis is enough oxygen to sustain fungal life in these marine ecosystems. What we don’t know is how these fungi access carbohydrates. Previous research by Küpper et al. 2006 has shown that these marine fungi can function as pathogens, latching on to their algal hosts, and feeding on their living tissue. Though, it is not irrational to think that over time, this habitat could yield complex mutualisms between plants and fungi. Both kingdoms have united forces independently several times throughout Earth’s long history. The difference here is that instead of marine plants just supplying their fungal counterpart with sugars in return for fungal scavenged nutrients, they could also trade oxygen; a resource terrestrial fungi don’t have to worry about.
Microdictyon umbilicatum consistently had the most fungal richness. Wainwright et al. 2017.
I just can’t get enough of this kingdom. Just when I think that I’m getting a mental grip on the fungal realm, I am thrown a fast curveball. I knew that marine fungi exist, and that benthic, oceanic habitats are where this kingdom first evolved, but I would have never believed that a single species can live in two drastically different ecosystems. More research needs to be conducted to find out how exactly the fungi access plant sugars. This is problematic too, with the rapid shift in the ocean’s chemistry. These deeper corals are safer from human disturbance than the reefs closer to the surface, but like I stated earlier, our planet is changing, and changing fast. We must learn about these habitats before it’s too late. We must show others how vastly complex Earth’s ecosystems are so we can team up to keep these diverse communities from becoming just a part of Earth’s history. I would love it if our children, and our children’s children have the chance to see these ecosystems in person and not just from books and blog posts.