Background
Invasive Species: a growing problem
The spread of invasive species is one of the worst ecological problems today as they can cause devastating repercussions to the environment and can alter whole ecosystems. The spread of invasive species is facilitated by the global activities of humans (e.g. ballast water from ships, pets, etc.) (Ruiz and Carlton 2003) but it has also been shown that climate change can increase the risk of the spread of invasive species, particularly in vulnerable regions such as the Arctic (Ruiz and Hewitt 2009). One such species which has become a growing concern in Arctic regions is the algae species Didymosphenia geminata (Figure 1 below).
A little about Didymosphenia geminata
Didymosphenia geminata is a type of diatom, which is a single-celled algae (Spaulding and Elwell 2007). Diatoms are one of the most numerous organisms and are found in almost every type of aquatic environment around the world. D. geminata differs from most diatom species as it forms an extracellular mucopolysaccaride stalk, which is used to create the massive colonies which results in the large mats seen in Figure 2.
Impacts of Didymosphenia geminata and importance of research
One of the consequences associated with a changing climate in the Arctic, is the possible alteration in the ecological communities, including a higher risk for invasive species to proliferate (Ruiz and Hewitt 2009). One such species is the diatom D. geminata, a colonial diatom that grows in enormously thick and rapidly forming mats. It can easily dominate the bottom substrates of a water body (particularly streams, Figure 3) (Kawecka and Sanecki 2003, Whitton et al. 2009). D. geminata can grow in such large abundances on a streambed that it can impact the ecological properties such as species diversity, fish migration routes and hatchery locations (Larned et al. 2006). The distribution of D. geminata is still being determined, but it has become widespread throughout North America, Europe, and most recently New Zealand (Whitton et al. 2009). Though native to boreal North American regions, the density and increased geographic distribution of D. geminata have recently become increasingly more apparent (Whitton et al. 2009). Large dense mats of D. geminata in streams of Arctic regions have now been reported. The Alaska Department of Fish and Game has reported many streams being infested, as well as some streams in the Yukon (Yukon Government, unpublished data), however only in more Southern regions to date.
With the threat of D. geminata proliferation increasing in the Arctic, a particularly valuable but also vulnerable environment, it is essential to determine what is driving its distribution.
With the threat of D. geminata proliferation increasing in the Arctic, a particularly valuable but also vulnerable environment, it is essential to determine what is driving its distribution.
Figure 3: A large colony of Didymosphenia geminata dominating a stream bed.
The drivers and vectors of Didymosphenia geminata: An ongoing debate
The earliest sighting of D. geminata was on Vancouver Island, British Columbia, but has since been found in streams worldwide (see Figure 4). It has been well established that the spread of D. geminata can be attributed to recreational activities (Spaulding and Elwell 2007). D. geminata can easily attach to boats and fishing gear (particularly felt-soled boots) which are then introduced to other areas.
The exact driver for the distribution of D. geminata infestations is still unclear, but there has been many different suggestions as to what the preferred environmental conditions are. Some of the suggested drivers are nutrient ratios (i.e. nitrogen to phosphorus), water flow and temperature.
The exact driver for the distribution of D. geminata infestations is still unclear, but there has been many different suggestions as to what the preferred environmental conditions are. Some of the suggested drivers are nutrient ratios (i.e. nitrogen to phosphorus), water flow and temperature.
Figure 4: Global distribution of Didymosphenia geminata. The red dots represent a rough geographic area of populations. Source: Spaulding and Elwell 2007.
Research objectives and possible outcomes
The main objective of this research was to determine the favoured environmental conditions of D. geminata and to determine the drivers for the distribution of this invasive species. By examining a wide range of streams in the Yukon and comparing the water chemistry and the physical and biological characteristics of the streams containing D. geminata with those that do not, we hoped to find a difference in the values of these environmental factors between the two sites (Presence versus Absence of D. geminata).
This data could provide important information regarding which type of stream environment D. geminata would most likely invade and proliferate in. Having this information would then allow managers to have a better idea on where to focus their energy and resources to prevent the further spread of D. geminata, and thus prevent further ecological damage. Management strategies which have been applied to other areas affected by D. geminata such as thorough cleaning of fishing gear and boats has had a fair success in limiting the spread of D. geminata and could be applied and enforced in areas that would be particuarly susceptible to the invasion, as determined from this study.
This data could provide important information regarding which type of stream environment D. geminata would most likely invade and proliferate in. Having this information would then allow managers to have a better idea on where to focus their energy and resources to prevent the further spread of D. geminata, and thus prevent further ecological damage. Management strategies which have been applied to other areas affected by D. geminata such as thorough cleaning of fishing gear and boats has had a fair success in limiting the spread of D. geminata and could be applied and enforced in areas that would be particuarly susceptible to the invasion, as determined from this study.