Bryophytes and their Roles in Freshwater Ecosystems (Portfolio)

This is a paper I wrote in my fresh water ecology course on research I did on mosses (again) in 2017.

Bryophytes and their Roles in Freshwater Ecosystems 

Cassidy Brennan

There are many factors that are involved in keeping a freshwater system healthy; it can be incredibly complicated and obscure. One group of organisms that can lend some insight into the health of a variety of freshwater ecosystems are bryophytic plants. Although normally identified as terrestrial plants, bryophytes have also been found to thrive in aquatic environments with considerable diversity. Bryophytes contribute to ecosystems by providing habitats, absorbing pollutants, and acting as indicator organisms regarding the health of various freshwater environments.


Bryophytes are seedless nonvascular plants that include mosses, liverworts, and hornworts. A diverse phylum, they are found in many varieties of freshwater environments but tend to be more present in clear fast moving rivers and streams than stagnant or brackish waters (Watson, 1919). In his article published by the British Ecological Society, Watson lists the many species he has studied and the types of water conditions they can be in. His records include descriptions of : mosses, liverworts, lichens (foliose and crustose), algae (unicellular and multicellular), and other organisms that he came across in his study. He describes the type of environment he was looking at, all the species he found there commonly, and some distinctions between them and their terrestrial counterparts with incredibly detailed examples:


Reduction of many structures often occurs in plants of wet places; the pores may be reduced (e.g. Marchantia), the ventral scales may become fewer or disappear (e.g. Dumortiera), or the hyaline cells may be relatively less (e.g. Sphagnum crassicladum). In Catharinea crispa the assimilating lamellae are fewer and lower than in the allied species of drier ground and a similar reduction sometimes occurs in submerged Polytricha: in fact, a wet ground form of P. gracile with reduced lamellae was at first described as a new species (Catharinea dixoni) and placed in a genus characterised by its few lamellae. The strengthening fibres of the hyaline cells of Sphagnum may also be fewer, but such reduction does not occur in Sphagna living in rapid streams. (Watson, p.75)





Although not all his notes are about bryophytes, Watson is thorough with his information and includes many examples of lichens and algae with his mosses and liverworts. He cites that lichens are not commonly submerged in water, but are found on rocks that are splashed often or partially submerged in the water with lists that include over a dozen species. Algae is very common with eight (+) species listed in his notes. Common bryophytes included over one hundred species with most of them being semi-submerged (Wason, 1919). The many species examples Watson listed shows the amount of diversity occurring in such a simple phylum. Among those lists are Fontinalis antipyretica and Platyhypnidium riparioides; two species that have commonly been used in monitoring pollutants in freshwater systems along with a few species of liverworts (Gecheva et al., 2014).


Bryophytes have been called “ecosystem engineers” because of their ability to modify landscapes and affect the biochemistry, biodiversity, and dynamics of the nutrients in an environment (Gecheva et al., 2014). Because bryophytes are so stress tolerant and can live in a variety of conditions, they are often looked to for information on the overall health and presence of pollutants in an area. In their paper, Gecheva and Yurukova discuss the usefulness of mosses and lichen such as Fontinalis antipyretica and Platyhypnidium riparioides, two species of moss that are often used as biomonitors because of how widespread they are in the Northern Hemisphere (Christy, 2006) and their usefulness as indicator species. They mention sensitive versus accumulative biomonitors, and how as accumulative biomonitors, mosses are indicators for heavy metal accumulation in freshwater ecosystems.


The physical structure of bryophytes is what provides the mechanism for them to be the useful indicators that they are. The lack of vascular tissue in the plants requires them to maintain close, and sometimes constant, contact with water to prevent the desiccation of the organism (Woodward, 2015). The near constant osmosis and diffusion that takes place between the outer tissue of the plant and its environment gives the accessibility to the variability of the chemical state of the water. This in turn allows the specimen to accumulate the elements and chemicals that scientists are looking to monitor.


The specific reasons P. riparioides is a good indicator is because it is so geographically and ecologically widespread making it a common species to sample and compare across the world. Along with that, P. riparioides is an excellent species to monitor heavy metals, low pH, and calcium levels that prevent proper species development; F. antipyretica is similarly valuable for detecting lead and zinc (Gecheva et al., 2014). Many other species were mentioned in their study including the liverwort Scapania undulata, which is known to be a species very tolerant of heavy metals. After analyzing samples of S. undulata in study sites, it was found that elevated pH and/or calcium can lead to increased accumulation of zinc, lead, and cadmium in a freshwater system. In their conclusion, Gecheva and Yurukova overview what makes bryophytes in freshwater such useful indicators, listing that things such as: the abundance of sample material that can be found throughout the year, the low cost of obtaining the material, the variety of freshwater systems that common species can be found in, and the ability to use passive or active monitoring with the species available (Gecheva et al., 2014).


Bryophytes are not only pollution tolerant, they also aid biodiversity through providing habitats and shelter for invertebrates. Bryophytes can alter the “hydraulic conditions” of the water they are in, and in doing so, provide a place for invertebrates (micro and macro) to rest and take shelter from predators (Johnston et al., 2015). Johnston and colleagues performed a study looking at the difference in diversity between oak leaf litter and bryophytes ( P. riparioides and N. compressa) in acidic waters versus circumneutral waters. What they found was that with more acidic conditions, colonization of bryophytes by invertebrates decreased compared to oak leaf litter. In circumneutral waters, they discovered that N. compressa and the oak leaf litter both held more organisms and diversity than P. riparioides. The difference in species inhabiting the bryophytes was not entirely surprising considering that one was a species of liverwort (N. compressa) and the other a moss (P. riparioides). The authors admitted in their conclusion that they did not get the results that they were expecting when it came to invertebrate species they found in their collections. There were families of invertebrates that they did not find on the bryophyte species that were sampled, that they expected to find based on research that has previously been done on the subject; this was credited to the collection methods that were used for the samples that Johnston and colleagues attained. The invertebrates could have washed away as the bryophytes were collected, families could have been misidentified, etc. Johnston (et al.) did, however mention that, “These results also support the conclusion that invertebrates do not inhabit bryophytes exclusively for the physical shelter they provide... shelter is of major functional importance [and] given that identical material was put into all the streams other conditions must also factor: we have insufficient data to indicate what those conditions may be.” Ultimately, it was their conclusion that both bryophytes and leaf litter provide important habitat for freshwater invertebrates. There is not a surprising difference in family variety, but the acidity of the environment does play an enormous role in preference between the two plant varieties for habitat and shelter. Johnston (et al.) stated that more studies would need to be done to discern the mechanisms that made these findings true.


An interesting comparison can be made between Johnston and her colleagues study and that of Glime and Clemons (1972) who did a study comparing how invertebrates respond to string and plastic substrates compared to real samples of a species of Fontinalis. Their results showed that there seemed to be little difference in preference between the real moss and the artificial substitutes. The overall diversity in species between the moss, string, and plastic was very similar, showing that there was not a drastic difference in preference for the insects. When it came to individual samples, however, there were the biggest differences in the counts on plastic compared to the string or real moss. The way this was calculated was dividing the number of times an insect occurred on a substrate divided by the number of collections. Ultimately the results lead to the conclusion that there was a definite preference for the true mosses.


Glime and Clemons agreed with Johnston (et al.) that the bryophytes are not used as food themselves so much as they are for habitat and shelter. They went on to describe the role the bryophyte plays in helping insects and other invertebrates with sourcing food; the amount of invertebrate diversity on a species sample of the bryophyte depends on how well it attracts a food source. This was demonstrated in their experiment with the artificial mosses not attracting a food source and therefore not being as heavily occupied or diverse. The most common invertebrate species found during the study were stoneflies and larval blackflies (Glime and Clemons, 1972).


As seen through multiple studies, freshwater bryophytes have a considerable impact on freshwater ecosystems. Their diversity and tolerance for many conditions makes them great bioindicators for the health of the water bodies in which they live. Besides their role in chemical monitoring, bryophytes provide habitat and shelter for many species of invertebrates as well as provide them with a food source. As stated in many of the studies, there is much more research potential when it comes to why bryophytes do as well as they do in certain environments, how they impact specific environments, as well as many other topics.
















References





Christy, John A.. J. A. (2006). Species Fact Sheet. Retrieved February 15, 2017, from U.S. Forest Service, https://www.fs.fed.us/r6/sfpnw/issssp/documents/planning-docs/sfs-br-platyhypnidium-riparioides-2010-05.pdf





Glime, J. M., & Clemons, R. M. (1972). Species diversity of stream insects of Fontinalis SPP. Compared to diversity on artificial substrates. Ecology, 53(3), 458–464. doi:10.2307/1934233





Glime, J. (1980). Effects of Temperature and Flow on Rhizoid Production in Fontinalis. American Bryological and Lichenological Society, 84(4), pp. 477–485. doi:10.2307/3242300





Gecheva, G., & Yurukova, L. (2014). Water pollutant monitoring with aquatic bryophytes: A review. Environmental Chemistry Letters, 12(1), 49–61. doi:10.1007/s10311-013-0429-z





Johnston, S. R., Vaughan, I. P., & Ormerod, S. J. (2015). Acid–base status mediates the selection of organic habitats by upland stream invertebrates. Hydrobiologia, (1),





Watson, W. (1919). THE BRYOPHYTES AND LICHENS OF FRESH WATER. British Journal of Ecology, 7(1/2), p71–83. 13p.





Woodward, D. (2015, May 18). Plants I: Evolution and Diversity, Nonvascular Plants. Retrieved from https://wikispaces.psu.edu/display/BIOL110F2013/Plants I - Evolution and Diversity, Nonvascular Plants.