Biological diversity: discovery, science, and management in this issue

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Figure 6. A researcher from the University of Gräz in Austria collects lichens during an inventory for Katmai National Park and Preserve.

NPS/Evan Heck

All data collected on nonvascular plant communities of Alaska’s national parks are making an important contribution to NPS resource management goals by documenting species diversity and changes in the structure and composition of ecological communities. As en -vironmental and anthropogenic stresses increase, Alaska’s I&M networks are establishing important baseline data sets that can be used to set benchmarks for measuring levels of ecological integrity. Continued and future investment in scientific capacity through partnerships with universities and other research institutions will further contribute to our understanding of nonvascular vegetation communities in Alaska’s national parks.


Ford, J., and L. Hasselbach. May 2001. Heavy metals in mosses and soils on six transects along the Red Dog Mine haul road, Alaska. Technical Report NPS/AR/NRTR–2001/38. National Park Service, Western Arctic National Parklands, Kotzebue, Alaska, USA. Available at

Hasselbach, L. 1995. Vascular and nonvascular vegetation of Aniakchak caldera, Alaska. Technical Report NPS/PNROSU/NRTR–95/05. National Park Service, Corvallis, Oregon, USA.

Hasselbach, L., J. Ver Hoef, J. Ford, P. Neitlich, E. Crecelius, S. Berryman, B. Wolk, and T. Bohle. 2005. Spatial patterns of cadmium and lead deposition on and adjacent to National Park Service lands in the vicinity of Red Dog Mine, Alaska. Science of the Total Environment 348(1–3):211–230.

Hinzman, L. D., N. D. Bettez, W. R. Bolton, F. S. Chapman, M. B. Dyurgerov, C. L. Fasti, B. Griffith, R. D. Hollister, A. Hope, H. P. Huntington et al. 2005. Evidence and implications of recent climate change in northern Alaska and other arctic regions. Climate Change 72:251–298.

Holt, E. A., B. McCune, and P. Neitlich. 2007. Succession and community gradients of Arctic macrolichens and their relation to substrate, topography, and rockiness. Pacific Northwest Fungi 2:1–21.

———. 2008. Grazing and fire impacts on macrolichen communities of the Seward Peninsula, Alaska, USA. The Bryologist 111:68–83.

Holt, E. A., and P. N. Neitlich. 2010a. Arctic Network Lichen Inventory Dataset. Geospatial Dataset—2166259. Available at /Profile/2166259.

———. 2010b. Lichen inventory synthesis: Western Arctic National Parklands and Arctic Network, Alaska. Natural Resource Technical Report NPS/AKR/ARCN/NRTR–2010/385. National Park Service, Fort Collins, Colorado, USA.

Joly, K., F. S. Chapin III, and D. R. Klein. 2010. Winter habitat selection by caribou in relation to lichen abundance, wildfires, grazing, and landscape characteristics in northwest Alaska. Ecoscience 17(3):321–333.

LaBounty, K. 2005. Nonvascular plants of Sitka National Historical Park. Report to the National Park Service, Juneau, Alaska, USA. Available at Report%202004.pdf.

Longton, R. E. 1992. The role of bryophytes and lichens in terrestrial ecosystems. Pages 32–36 in J. W. Bates and A. M. Farmer, editors. Bryophytes and lichens in a changing environment. Clarendon Press, Oxford, UK.

McCune, B., E. Holt, P. Neitlich, T. Ahti, and R. Rosentreter. 2009. Macrolichen diversity in Noatak National Preserve, Alaska. North American Fungi 4(4):1–22.

McCune, B., T. Tønsberg, P. Nelson, K. Spickerman, L. Muggia, M. Schultz, R. Rosentreter, T. Esslinger, J. Sheard, J. Miadlikowska et al. 2017. Lichen inventory of the Southwest Alaska Network. Natural Resource Technical Report. National Park Service, Fort Collins, Colorado, USA. In preparation.

National Park Service (NPS). 2009. Strategic plan for natural resource inventories: FY2008– FY2012. Natural Resource Report NPS/NRPC/ NRR–2009/094. National Park Service, Fort Collins, Colorado, USA.

Neitlich, P., and L. Hasselbach. 1998. Lichen inventory and status assessment for Gates of the Arctic National Park and Preserve, Alaska. Generic Document–2166292. National Park Service, Fort Collins, Colorado, USA.

Neitlich, P. N., J. Ver Hoef, S. B. Berryman, A. Mines, and L. Geiser. 2014a. Effects of heavy metal–enriched road dust from the Red Dog Mine haul road on tundra vegetation in Cape Krusenstern National Monument, Alaska. NPS Natural Resource Technical Report. In preparation.

———. 2014b. Remeasurement of spatial patterns of heavy metal deposition on National Park Service lands along the Red Dog Mine haul road, Alaska. NPS Natural Resource Technical Report. In review.

Nelson, P., B. McCune, T. Wheeler, and D. Swanson. 2014. Lichen communities of Gates of the Arctic National Park, Alaska. Natural Resource Report Series. National Park Service, Fort Collins, Colorado, USA. In preparation.

Schirokauer, D., L. Geiser, E. Porter, and B. Moynahan. 2008. Monitoring air quality in the Southeast Alaska Network: Linking ambient and depositional pollutants with ecological effects. NPS-KLGO, 2008 Implementation Plan. National Park Service, Skagway, Alaska, and U.S. Forest Service, Corvallis, Oregon, USA. Available at

Spribille, T., S. Pérez-Ortega, T. Tønsberg, and D. Schirokauer. 2010. Lichens and lichenicolous fungi of the Klondike Gold Rush National Historic Park, Alaska, in a global biodiversity context. The Bryologist 113(3):439–515.

Stehn, S., P. Nelson, C. Roland, and J. Jones. 2013a. Patterns in the occupancy and abundance of the globally rare lichen Erioderma pedicellatum in Denali National Park and Preserve, Alaska. The Bryologist 116(1):2–14.

Stehn, S., J. Walton, and C. Roland. 2013b. A bryophyte species list for Denali National Park and Preserve, Alaska, with comments on several new and noteworthy records. Evansia 30(1):31–45.

Turetsky, M. R. 2003. The role of bryophytes in carbon and nitrogen cycling. The Bryologist 106:395–409.

Turetsky, M. R., M. C. Mack, T. N. Hollingsworth, and J. W. Harden. 2010. The role of mosses in ecosystem succession and function in Alaska’s boreal forest. Canadian Journal of Forest Resources 40:1237–1264.

Walton, J. K., M. Hutten, and S. K. Torigoe. 2014. Inventory of the mosses, liverworts, and lichens of Kenai Fjords National Park, Alaska: 2013 Progress Report. Natural Resource Data Series Report NPS/SWAN/NRDS–2014/635. National Park Service, Fort Collins, Colorado, USA.

About the authors

James Walton ( is a botanist with the Southwest Alaska Network in Anchorage, Alaska. Sarah Stehn ( is a botanist with the Central Alaska Network in Denali National Park and Preserve, Alaska.

All along the watchtower: Larval dragonflies are promising biological sentinels for monitoring methylmercury contamination

By Roger J. Haro


Humans have used other organisms to detect environmental danger for centuries (e.g., the canary in the coal mine). The use of “biosentinels” has developed and expanded to become a mainstay for monitoring environmental contaminants like methylmercury, a pervasive and largely anthropogenic neurotoxin. Biosentinels provide insights on how and where contaminants are entering and moving through aquatic food webs. Many water bodies in the Great Lakes region, including those in national park units, have fish-consumption advisories because of the atmospheric deposition of mercury and its conversion into methylmercury, which can biomagnify. For many years young yellow perch served as the principal biosentinel for monitoring methylmercury. Resent research shows that the diverse assemblage of dragonflies in this region can provide an additional suite of biosentinels, complementing the use of perch among water bodies with fish and expanding the reach of methylmercury monitoring to include fishless ecosystems (e.g., small ponds and wetlands).

Key words

biosentinels, contaminant monitoring, dragonfly larvae, fish-consumption advisories, methylmercury

In the popular fantasy series Game of Thrones, the Night’s Watch portrays vigilant sentinels silently watching for trouble and sending word to the people behind the wall to prepare and react if danger approaches. Humans similarly rely on biological sentinels to detect dangerous substances in the environment and depend on them as early warning signals. Stories about the sensitive canary succumbing to low levels of toxic gases, alerting miners to take evasive action, illustrate the idea of a biological sentinel. Now, instead of bringing the canary to the site of a potential hazard, scientists and resource managers are recognizing the importance of the stories that resident organisms can convey about the environmental condition or health of their ecosystems. These organisms are called biological sentinels or, simply, biosentinels. The diversity of organisms in an ecosystem provides an array of candidate biosentinels, each one telling a slightly different story about the environmental health of the local environment.

Today the stories told by biosentinels can be vastly more informative than a simple signal that it is time to leave the mine. These stories can reveal the risk of exposure to contaminants such as methylmercury. The organisms are sampled after accumulating the contaminants from their environment, and their tissues are then analyzed to estimate the contaminant concentration. These analyses can provide clues to how and where a contaminant entered the biosentinel. The story can expand to identify other players, for example how contaminant levels in the biosentinel are transferred to predators, or how their own dietary preferences and feeding behaviors affect their exposure to bioaccumulative contaminants that are transferred in food webs. Thus the stories biosentinels tell can be extremely informative and useful.

Useful biosentinels are those organisms that consistently “integrate” uptake of contaminants over a range of concentration in both space and time. The bioavailability of a contaminant to an organism depends not only on the biogeochemical behavior of the contaminant but also on specific traits involving the life history, physiology, and trophic ecology of the organism. Any combination of conditions and traits that would prevent or limit the organism’s exposure to a specific contaminant lowers its value as a potential biosentinel. Another practical consideration is the ease with which the organism can be collected, identified, and analyzed. If such conditions are satisfied, biologists and re source managers weigh the cost-effective ness of using a specific biosentinel. This is especially important if the biosentinel is to become part of a sustained monitoring program. Such practical considerations have focused attention on larval dragonflies as potential new biosentinels for monitoring methylmercury contamination in freshwater systems, especially in our national parks.

Mercury in the environment

Mercury (Hg) is a naturally occurring element in the environment, but human sources now contribute about 70% of the mercury in the atmosphere. The atmospheric transport and deposition of mercury in both dry and wet forms pose a considerable threat to areas far from traditional point sources of mercury, such as mines and industrial sources. Lacking local, geologic mercury sources, organic methylmercury is formed from inorganic mercury that has been atmospherically deposited and transformed by mercury-methylating bacteria, which can occur naturally, for example, in the shallow sediments of lakes and wetlands. Take Ryan Lake in Voyageurs National Park as an example: a gorgeous, southern boreal lake surrounded by rugged rock outcroppings and white pines. Located in northern Minnesota near the Canadian border, the lake is accessible only by boat and a 1.5-mile (2.4 km) hike. Yet the predatory fish inhabiting its tea-stained waters have the highest known concentrations of methylmercury documented for any lake in Minnesota. Mercury in the form of methylmercury bioaccumulates and biomagnifies through the Ryan Lake food web so that a filet of a northern pike contains more than 1,000 parts per billion of Hg, a concentration exceeding the U.S. Environmental Protection Agency’s fish-tissue criterion for methylmercury (300 parts per billion wet weight), which was established to protect the health of humans who eat noncommercial fish. The risk of neurological damage to humans from eating contaminated fish, like the northern pike from Ryan Lake, prompted the issuance of fish-consumption advisories for thousands of water bodies throughout the United States, including many in our national parks. This problem is exacerbated by the sensitivity of certain water bodies to mercury pollution, which is highly location-specific and depends on a number of physical, chemical, and land scape factors. For example, the mercury concentration in prey fish and predatory fish can vary almost 10-fold among inland lakes of Voyageurs National Park (Wiener et al. 2006).

As states and nations strive to reduce anthropogenic emissions of mercury into the atmosphere, how will we know whether concentrations of methylmercury in food webs, fish, and wildlife respond and decline? Conversely, how will we know whether mercury emissions from distant but rapidly developing nations like China are impacting our aquatic ecosystems? How can we adequately expand our understanding of a contaminant that displays such high spatial and temporal variability? For freshwater ecosystems in the Great Lakes region, such challenges may require the monitoring of biosentinel organisms beyond those that have been used.

Use of small prey fish as biosentinels

As the scope of the mercury deposition problem became evident to scientists and resource managers in the 1980s, they soon realized that there were key contaminant transfer points in affected food webs. One was the pathway for human exposure from the consumption of contaminated sport fish. However, there were other vulnerable end points in the food web, such as the common loon, an iconic avian piscivore in Canada and the United States. This is where small yellow perch (Perca flavescens) come into the story. As young fish, they serve as an important trophic link to both game fish, such as northern pike and walleye, and breeding common loons that nest and raise their young in northern lakes. It is not surprising that the yellow perch became an important biosentinel for monitoring mercury in many lentic waters (e.g., lakes, ponds, or swamps) (Wiener et al. 2007). Yellow perch are ubiquitous and often very abundant in the northern temperate and boreal lakes of North America. They are found in a wide array of water quality conditions, from soft, poorly buffered, low-pH lakes to hard-water marl lakes. Numerous studies have shown that the concentration of mercury in one-year-old yellow perch is strongly correlated with the mercury concentration of coexisting game fish. Their distribution in lakes surrounding the industrial Rust Belt of North America and their intermediate position in the food webs of those lakes have made small yellow perch an effective biosentinel for monitoring methylmercury in much of the eastern United States and Canada.

There are limitations to the use of yellow perch and other small prey fishes as biosentinel organisms. Although yellow perch are often abundant in lentic systems, they do not typically inhabit lotic habitats (i.e., those characterized by fast-moving water) and certain wetlands, such as bogs and ephemeral ponds. Moreover, recent research has shown that emergent aquatic insects from fishless water bodies can be important points of methylmercury transfer to terrestrial consumers, such as spiders, invertivorous birds, and bats (Blackwell and Drenner 2009).

Larval dragonflies as biosentinels for mercury

A diverse assemblage of dragonflies inhabits the aquatic environs surrounding the Great Lakes (fig. 1). Upon emergence as adults, they are conduits for the transfer of methyl mercury from the aquatic to the terrestrial ecosystem. These insects are promising biosentinels of methylmercury in aquatic food webs, given that they inhabit a diverse array of aquatic and wetland habitats and their use as biosentinels can extend the assessment of food web contamination to fishless aquatic habitats. All dragonfly larvae are obligate predators, bioaccumulate methylmercury (fig. 2), and are restricted to the water body where they were hatched. Most are identifiable to species, and sufficient numbers and sample mass can be readily obtained with simple, inexpensive gear (e.g., a D-shaped net). Their ecology is well documented at the genus level, which greatly facilitates and enhances the interpretation of data from chemical analysis of larvae.

[Graph showing the number of dragonfly species by family recorded across counties containing six national park study units of the National Park System in the Great Lakes region, as follows: Skimmers: 38; Clubtails: 30; Emeralds: 21; Darners: 20; Spiketails: 4; and Cruisers: 3]

Figure 1. Number of dragonfly species by family recorded across counties containing six national park study units in the Great Lakes region. In total, 116 species of dragonflies (Anisoptera) were record ed. Common names for each dragonfly family appear above each bar. Species distribution data were derived from Abbott (2007). Graph showing the relation between mean (±SE) concentrations of MeHg in burrowing gomphid larvae and unfilter ed water from 17 lakes in the northwest Laurentian Great Lakes region. The trend line reveals rising mean MeHg concentration in Gomphid larvae as the mean MeHg concentration in unfiltered lake water rises.

[Graph showing the relation between mean (±SE) concentrations of MeHg in burrowing gomphid larvae and unfiltered water from 17 lakes in the northwest Laurentian Great Lakes region. The trend line reveals rising mean MeHg concentration in Gomphid larvae as the mean MeHg concentration in unfiltered lake water rises.]

Figure 2. Relation between mean (±SE) concentrations of MeHg in burrowing gomphid larvae and unfiltered water from 17 lakes in the northwest Laurentian Great Lakes region. Data for coexisting species of burrowing gomphids were combined to estimate mean MeHg in larvae for each lake. Means for MeHg in water were cal culated from samples collected in 2010, 2011, and 2012. Means for gomphids were calculated from samples collected in 2008, 2009, and 2010. The linear regression model is shown as a solid line.

The utility of burrowing dragonfly larvae as biosentinels of methylmercury in aquatic food webs has been examined by Haro et al. (2013), who collected late-instar (i.e., individuals near maturity and adult emergence from the aquatic environment) dragonfly larvae in the genus Gomphus spp. (clubtails) from 17 inland lakes in four national parks in the western Great Lakes region (Isle Royale National Park, Pictured Rocks National Lakeshore, Sleeping Bear Dunes National Lakeshore, and Voyageurs National Park). They conducted a statisti cal analysis to determine the number of dragonflies to collect in order to detect a 20% difference in mean total mercury concentration in their tissue from a lake. The same was calculated for young yellow perch sampled from the same group of lakes. The results indicated that only 10 dragonfly larvae needed to be sampled, whereas 40 yellow perch were required (fig. 3). In the Great Lakes region, the logistical advantages are clear for adding dragonfly larvae as biosentinels for mercury monitoring. The sampling gear required for collecting age-one yellow perch is more difficult to carry into hard-to-reach lakes like those in the rugged interior of Isle Royale. Nevertheless, if lakes of interest are close to one another, it is not unreasonable to expect that multiple lakes could be sampled in a single day using dragonfly larvae as biosentinels. Their ease of collection is also a strong impetus for their use in a nationwide citizen science–based monitoring program (see the article by Flanagan Pritz et al.).

[Graph showing the estimated sample sizes (i.e., the numbers of individuals required) needed to detect differences in concentration of total mercury (THg) in small, whole yellow perch (total length = 76 mm or 2.9 in) and larval Gomphus in lakes of the northwestern Great Lakes region.]

Figure 3. Estimated sample sizes (i.e., the numbers of individuals required) needed to detect differences in concentration of total mercury (THg) in small, whole yellow perch (total length = 76 mm or 2.9 in) and larval Gomphus in lakes of the northwestern Great Lakes region with a Type I error (α) of 0.05 and a statistical power (1-ß) of 0.80.

More research is needed on the mecha nisms behind the uptake of methylmer cury as well as on its trophic transfer from larval dragonflies. The larvae obtain their oxygen by actively drawing water into their rectum, where their gills reside. This rectal ventilation may be an additional pathway for the uptake of methylmercury. Furthermore, behavioral and physiological differences among the taxonomic families of dragonflies may also affect the uptake of methylmercury. These issues will provide important lines for additional research. These unanswered questions do not detract from the fact that larval dragon flies are a new and potentially powerful biosentinel for expanding our ability to assess mercury in the waters of our national parks and beyond.

Literature cited

Abbott, J. C. 2007. Odonata central: An online resource for the Odonata of North America. Austin, Texas, USA. Available at

Blackwell, B. D., and R. W. Drenner. 2009. Mercury contamination of macroinvertebrates in fishless ponds. Southwest Naturalist 54:468–474.

Haro, R. J., S. W. Bailey, R. M. Northwick, K. R. Rolfhus, M. B. Sandheinrich, and J. G. Wiener. 2013. Burrowing dragonfly larvae as biosentinels of methylmercury in freshwater food webs. Environmental Science and Technology 47:8148-8156.

Wiener, J. G., R. A. Bodaly, S. S. Brown, M. Lucotte, C. Newman, D. B. Porcella, R. J. Reash, and E. B. Swain. 2007. Monitoring and evaluating trends in methylmercury accumulation in aquatic biota. Pages 87–122 in R. Harris, D. P. Krabbenhoft, R. Mason, M. W. Murray, R. Reash, and T. Saltman, editors. Ecosystem responses to mercury contamination—Indicators of change. CRC Press, Boca Raton, Florida, USA.

Wiener, J. G., B. C. Knights, M. B. Sandheinrich, J. D. Jeremiason, M. E. Brigham, D. R. Engstrom, L. G. Woodruff, W. F. Cannon, and S. J. Balogh. 2006. Mercury in soils, lakes, and fish in Voyageurs National Park: Importance of atmospheric deposition and ecosystem factors. Environmental Science and Technology 40:6261–6268.

About the author

Roger J. Haro ( is an aquatic entomologist and professor of biology at the University of Wisconsin–La Crosse. He is the assistant director for the UW–La Crosse River Studies Center, a research center with more than 30 years of history studying the delivery and movement of methylmercury through aquatic food webs.

The Call to Action Collect Dragonflies

Citizen scientists study mercury contamination in national parks

By Colleen Flanagan Pritz, Sarah Nelson, and Collin Eagles-Smith

It’s a crisp august morning at Lily Lake, Rocky Mountain National Park. Twelve Arizona high school students arrive at the parking lot, beaming with excitement about their journey to Colorado and the adventures that await them, all dressed in the same green-colored T-shirts: “BioBlitz.” The year is 2012. They grab nets and waders, magnifying glasses, and field guides; some wear GoPros to video-record the experience. They head for the lakeshore in search of little bugs that live in the water. But not just any little bugs … dragonfly larvae.

The students—citizen scientists—seek out little faces with two big, beady eyes and a sinister “smile” made of extending (prehensile) mouthparts, an apparatus with jagged, grasping edges used to snatch prey and devour it whole. This underwater creature is the dragonfly in its larval stage, before it morphs into the colorfully aerial, adult dragonfly we all know.

Dragonfly larvae are widespread across the United States and are an important food source for fish, amphibians, and birds. They live underwater for up to five years before undergoing incomplete metamorphosis. At this time they crawl out of the water onto emergent vegetation, the shore, a dock, a rock, or any dry place, then shed their exoskeleton, dry their wings, and fly off. Robert DuBois, naturalist and author of the field guide Dragonflies and Damselflies of the Rocky Mountains, describes the transformation: “After months or years of clambering about underwater, the nymph is freed from the shackles of this ignoble existence in one grand moment of emancipation. Almost instantly it becomes one of the most graceful, elegant, and masterful flying creatures under the sun.”

A student steps out from the cattails and asks, “Is this one?” She hands over a shallow plastic spoon holding a bug, about 10 millimeters (0.4 in) in length, eyes very large in proportion to its head, wriggling in a thin veil of water.

How many legs does it have?”

“Six,” she replies.

Would you call the abdomen slender or bulky?”

“It’s skinny and long,” she says with certainty.

What are those three feathery things extending from the tip of the abdomen?”

“Hmm.” She pages through the field guide. “Gills?”


She pauses. “Is it a dragonfly nymph?” She looks back at the book.

“Aw, man! It’s a damsel-fly…”

Keep looking. You were close!”

Thanks to the foundation laid by the Acadia Learning Project, an opportunity arose to engage citizen scientists in a project that both educates participants about park science and provides parks with valuable environmental information.

[A student searches for dragonfly larvae on the banks of Lily Lake, Rocky Mountain National Park, Colorado. Credit: Copyright National Geographic Society/Karine Aigner]

[A schoolgirl inspects a small net alongside a park ranger in search of dragonfly larvae. Credit: Copyright National Geographic Society/Karine Aigner]

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