Diatom of the Month June 2019 - Subarctic diatom metacommunity

Subarctic streams hold almost pristine type of communities, which makes them highly valuable sentinel ecosystems to predict global change impacts.

Marja Lindholm* shares her research about diatoms, functional responses and spatial factors in Subarctic catchments

 

 

If you are travelling in the northernmost parts of Europe, you will see pristine-looking small streams and rivers flowing through the subarctic landscape (Fig. 1).

Figure 1. Streams in subarctic landscape (Picture: M. Grönroos, 2012).

 

If you look at those streams more closely, you will see clean-looking or moss-covered stones through clear water in the bottom of riffle sites (Fig. 2). Unless you were well informed already about this, you probably would never think that the surfaces of those spotless stones and moss host thriving communities of microscopic organisms, such as algae and bacteria.

Figure 2. Clear looking stones at the bottom of the subarctic stream (Picture: M. Grönroos, 2012).

 

One important group of microscopic unicellular algae are the fascinating glass-encased diatoms (Fig. 3), crucial primary producers in those barren looking streams. These diverse algae, invisible to the naked eye, provide food to consumers, such as macroinvertebrates (bugs living in those streams), produce oxygen and recycle nutrients.

 

 

Figure 3. Some of the diatoms we sampled in a subarctic stream (Picture: M. Lindholm, 2013).

 

These intriguing species are also widely used as ecological indicators to assess water quality. It is therefore essential to know and understand how diatom communities full of different species relate to conditions in pristine-looking stream sites where they live and the surrounding environment, and the location with respect to other streams in the landscape.

 

In early summer 2012, we explored fifty-five almost pristine subarctic streams. These streams flow to the river Teno, located at the border between Finland and Norway, which then flows to the Tanafjord in the Arctic Ocean. We sampled diatoms, macroinvertebrates (the bugs mentioned above), and bacteria. The diatom sampling, believe it or not, was done by toothbrush (Fig. 4), which is a common, cheap way of doing it that attracts funny comments by bemused friends and relatives. We also took many measurements, such as current velocity, conductivity and shading by riparian vegetation, from the stream site and the surrounding shore area.

Figure 4. Diatom sampling was done by toothbrush (Picture: M. Grönroos, 2012).

 

This fieldwork was part of the project ‘Spatial scaling, metacommunity structure and patterns in stream communities’ funded by the Academy of Finland. Metacommunities are groups of local communities of multiple potentially interacting species that are linked by dispersal (Wilson 1992; Leibold et al. 2004). Metacommunities have often been treated as a whole, without any systematic division in different organismal groups or different biological and ecological characteristics of different species.

 

I was lucky to conduct my Master’s thesis on these subarctic diatom communities. We wanted to know whether and how diatom species with different traits relate to their environment and spatial factors (geographical structure of the sites) in different ways. We divided the diatom species into four different ecological guilds. The guild classification was based on the potential of species to use nutrient resources and to resist physical perturbation (Passy 2007; Rimet & Bouchez 2012). In addition, we also divided our species into generalists (taxa showing broad ranges of tolerance to environmental conditions) and specialists (taxa showing narrow ranges) based on their ecological specialisation. We found that these groups have different relationships with local and catchment conditions and spatial factors and that the composition of diatom communities in subarctic streams is determined by environmental and spatial processes. Our findings also suggest that deconstructing the whole community into different groups by species traits increase our understanding of stream diatom metacommunity organisation (Lindholm et al. 2018).

 

As the climate is changing rapidly, especially in the arctic and subarctic areas (IPCC 2014), and anthropogenic pressures are growing globally, it is important to study these unique and nearly pristine ecosystems and their spatial connectivity now that they still exist. More important, however, is to protect these ecosystems and to reduce carbon dioxide emissions and habitat fragmentation, so that they and these wonderful, still little-known communities of microorganisms can continue to thrive and evolve for millennia to come.

 

* Geography Research Unit, University of Oulu

 

Please leave a comment below, or send an email to Marja if you have comments or questions about the post.

Visit Marja’s research media outlets at Physical Geography Research Group, Large-Scale Ecology Laboratory ResearchGate, Twitter & Instagram to know more about her research.

 

 

 

References:

IPCC (2014). Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Field, C.B., et al. eds.). Cambridge University Press, Cambridge, United Kingdom.

Leibold, M. A., M. Holyoak, N. Mouquet, P. Amarasekare, J. M. Chase, M. F. Hoopes, et al., (2004). The metacommunity concept: a framework for multi-scale community ecology. Ecology Letters 7: 601–613. https://doi.org/10.1111/j.1461-0248.2004.00608.x

Lindholm, M., Grönroos, M. Hjort, J. Karjalainen, S. M., Tokola, L. & Heino, J. (2018). Different species trait groups of stream diatoms show divergent responses to spatial and environmental factors in a subarctic drainage basin. Hydrobiologia 816: 213–230. http://doi.org/10.1007/s10750-018-3585-0

Passy, S.I. (2007). Diatom ecological guilds display distinct and predictable behavior along nutrient and disturbance gradients in running waters. Aquatic Botany 86: 171–178. https://doi.org/10.1016/j.aquabot.2006.09.018

Rimet, F. & Bouchez A. (2012). Life-forms, cell-sizes and ecological guilds of diatoms in European rivers. Knowledge and Management of Aquatic Ecosystems 406: 1–14. https://doi.org/10.1051/kmae/2012018

Wilson, D. S. (1992). Complex interactions in metacommunities, with implications for biodiversity and higher levels of selection. Ecology 73: 1984–2000. https://doi.org/10.2307/1941449