Tristan Wang ’16, THURJ Staff
It is no surprise that there are many gross things in this world. Perhaps it is the stench of a ripe foot on a hot day or a bathroom stall surprise that turns your stomach. Maybe it is the banana peel forcing you to take out your trash. Even the creepy crawly cockroach running across your room is no match for the stink from opening up an old fridge (wait, the month-old Chinese take-out in the fridge is not supposed to be fuzzy?) But there is more to fungi than just gross mold and that mushroom character people impersonate in Mario-cart. In fact, like finding that month-old Chinese food in your fridge, it may come as a surprise that the vast majority of aquatic fungi – a small but ecologically important group – have not been explored yet.
The largest biodiversity of aquatic fungi currently reside in temperate regions; this is most likely because only a small number of experts in the field explore the more tropical zones (1). Only about 3000 out of the estimated one and a half million fungal species have been associated to aquatic environments (1). Although they make up a small proportion of all fungi, underwater fungi prove to be significant forces in shaping the ecological and human world. Their roles in nutrient cycling and natural symbiotic relationships only just touch upon their larger importance, as further exploring their world may prove fruitful to humans as well.
The vast diversity of underwater fungi (both marine and aquatic, which are fungi that live in saltwater and freshwater environments respectively) reflects the variety of conditions that fungi can inhabit. Indeed, environmental conditions like water salinity, acidity and especially temperature are important factors that influence the growth of certain marine fungi (2). Marine fungi environments can range from tropical waters (such as those of Antennospora quadricornuta) to much cooler arctic waters (like those of Slathulospora antartica) (2). Some marine fungi (including Lindra inflate) depend on fully saline waters while others need brackish (a mixture of salty and fresh water) or slightly salted waters to live (2). In addition, the types of substrates on which the fungi grow may influence the species’ diversity as well. For example, it has been noted that mangroves prove to be some of the richest environments not just for invertebrates, but also fungi (2). There have been several reports of saltwater lichens and fungi that live on and off of corals (1, 3). Certain species of endolithic fungi –fungi capable of living on stone –have even found ways to penetrate carbonate sources in saltwater like limestone, corals or mollusk shells (3). Thus, the diversity of marine fungi cannot be underestimated. However, while interesting, marine fungi have not been studied extensively, which is likely due to the lack of specialists in the field.
In terms of research material, aquatic fungi have fared better than their marine counterparts. Fungal biodiversity in aquatic habitats also depends on water conditions such as temperature and nutrient density, but because of their heterotrophic nature, aquatic fungi in addition heavily rely on external organic matter to continue feeding themselves (4). For example, aquatic hyphomycetes (molds) are anamorphic fungi (fungi with an asexual reproductive stage) that survive in quick flowing waters by feeding on decaying leaves and woody fallout (1). Many of their spores often land in foams on the water surface (1). Other species of freshwater meiosporic ascomycetes (think truffles, lichens and mildews) have made fewer appearances; In fact, about 70% of freshwater ascomycetes have not been reported more than once (1). Thus, it is difficult to assess the diversity of aquatic fungi if there is no thorough sampling. Probably the most infamous aquatic fungus is the fungal pathogen Batrachochytrium dendrobatidis, a chytrid fungus that attacks frogs by infecting their skin (1,5). It has been described as “the most spectacular loss of vertebrate biodiversity due to disease in recorded history” (5).
While headlines of “Devastating Chytrids” or “Fungal Pathogens” have the public pointing fingers at fungi as an evil entity, underwater fungi prove to be some of the most beneficial and important molding factors of their ecosystems simply by doing what they do best: eating. Aquatic ecosystems tend to have fewer key herbivores than terrestrial ecosystems and consequently decomposers must pick up the slack in their roles in transferring nutrients and energy back into their ecosystem (4). Fungi often employ enzymes capable of breaking down highly complex substances shed by plants which bacteria in turn can feed on (4). In particular, aquatic hyphomycetes are well adapted to cooler environments and in temperate waters filamentous fungi can account up for 90% of total microbial biomass during the winter (4). In addition, underwater fungi interact with a variety of organisms in both marine and freshwater environments. It may be possible in the future to exploit the voracious appetite of underwater fungi through potential use of fungi in sewage systems. The quick growth of fungi also positions them well as potential players in bioremediation when pollution is at hand.
Like on land, aquatic fungi are capable of forming mutualistic relationships with plants through mycorrhizal interactions (6). Forming interconnected structures with the roots of plants, the mycorrhizal fungi extend the plant’s reach of nutrients in return for some of the plant’s energy (6). Taking advantage of their digestive capabilities, marine fungi are also capable of growing on and degrading a variety of substrates like chitin, keratin and lignin (1), which allows them to grow on mollusks and corals (1,3). However, fungal growth can also be detrimental to corals, especially when corals are under environmental stress, which makes them particularly prone to attacks by marine fungi (3). Freshwaters also harbor strong parasitic relationships among fungi and their neighbors. During a plant’s decline, aquatic fungi are often found to be the first major invasive organism (7). In many pelagic ecosystems, fungi heavily influence the phytoplankton community (4). One species called Zygorhizidium plaktonicum can even infect up to 90% of the population of freshwater diatoms (4). This can be devastating considering that diatoms are often known to be in important food source for higher trophic levels of consumers.
Given the opportunity, fungi will obviously make themselves at home in practically any environment. They are as ubiquitous as we are and perhaps even more so, but it is hardly true to say that we know everything about them. It is currently estimated that fungal diversity overshadows that of any other microbial group, consequently making underwater fungi very diverse indeed(4). The importance of underwater fungi cannot be underestimated and research should continue to explore their diversity and important roles in underwater ecosystems. If harnessed by humans, several species of underwater fungi could prove to be very useful. Of course, that is not surprising considering that underwater fungi are resilient enough to colonize the frigid waters of the arctic and the warm tropical waters of coral reefs. The famous actor Adam Baldwin hit the mark when he stated that “I’m like a fungus; you can’t get rid of me.” Of course considering how interesting these little critters are, why would you?
- Shearer, Carol A., Enrique Descals, Brigitte Kohlmeyer, Jan Kohlmeyer, Ludmila Marvanová, David Padgett, David Porter, Huzefa A. Raja, John P. Schmit, Holly A. Thorton, and Hermann Voglymayr. “Fungal Biodiversity in Aquatic Habitats.” Biodiversity and Conservation 16.1 (2007): 49-67.
- Jones, Gareth E.B. “Marine Fungi: Some Factors Influencing Biodiversity.” Fungal Diversity 4 (2000): 53-73.
- Golubic, Stjepko, Gudrun Radtke, and Therese Le Campion-Alsumard. “Endolithic Fungi in Marine Ecosystems.” Trends in Microbiology 13.5 (2005): 229-35.
- Wurzbacher Christian, Kerr Janice and Grossart Hans-Peter (2011). Aquatic Fungi, The Dynamical Processes of Biodiversity – Case Studies of Evolution and Spatial Distribution, PhD. Oscar Grillo (Ed.), ISBN: 978-953- 307-772-7, InTech, Available from: http://www.intechopen.com/books/the-dynamical-processes-of-biodiversity- case-studies-of-evolution-and-spatial-distribution/aquatic-fungi
- Skerratt, Lee Francis, Lee Berger, Richard Speare, Scott Cashins, Keith Raymond Mcdonald, Andrea Dawn Phillott, Harry Bryan Hines, and Nicole Kenyon. “Spread of Chytridiomycosis Has Caused the Rapid Global Decline and Extinction of Frogs.” EcoHealth 4.2 (2007): 125-34.
- Stenlund, Dwayne L., and Iris D. Charvat. “Vesicular Arbuscular Mycorrhizae in Floating Wetland Mat Communities Dominated by Typha.” Mycorrhiza 4.3 (1994): 131-37.
- Motta, Jerome J. “The Occurrence of Fungi on Some Rooted Aquatics from the Chesapeake Bay.” Estuaries 1.2 (1978): 101.