Vanishing glaciers

The sky was cloudless, a spotless expanse of endless blue, and not a single breath of wind rippled the water of Bowman Lake, a long and slender finger of water nestled between two ridges in the northwestern corner of Glacier National Park.

After growing up on the east coast, nine years ago this summer I visited the American West for the first time, and I understood why Montana is nicknamed “Big Sky Country.” I spent eight weeks at the University of Montana’s Flathead Lake Biological Station, where my fellow students and I dove into our field ecology classes, exploring the mountains and lakes of northwestern Montana along the way.

We visited Glacier National Park on several of our field trips, and one day in particular sticks in my mind – the lake was a perfect mirror for the mountains and the sky, and it was too beautiful for us to leave without taking out our cameras.

The sky and surrounding ridges reflected in Bowman Lake, along with several other photographers, in mid-summer 2006.

(Image by Emily Benson)

The majestic scenery of Glacier National Park, however, is changing – scientists estimate that by 2030, all of the park’s glaciers will be gone, melted under the force of global climate change. As the National Park Service notes, “the park’s glacially fed streams provide a constant flow of cold water throughout the summer season, maintaining necessary water levels and regulating stream temperature for fish and other aquatic species. Plant and animal species throughout the park rely on this flow.”

One of those animal species is the western glacier stonefly, an aquatic insect that, in the past, has only been found in alpine streams in Glacier National Park.

Recently, a group of scientists (including one of the professors that I studied with during my summer in Montana) surveyed all of the locations where the western glacier stonefly has been found in the past, as well as some similar habitats, in order to determine whether their distribution is shrinking along with the glaciers in the park.

The researchers detected western glacier stoneflies in only one of the six streams where they’ve been found before; they also found the stoneflies in two new alpine sites within the park, as well as one site about 335 miles away in Grand Teton National Park.

The scientists note that further study on the “status, distribution, and vulnerability” of the western glacier stonefly is warranted, but the results they’ve already gathered “suggest that an extremely restricted historical distribution of [the western glacier stonefly] in [Glacier National Park] has been further reduced over the past several decades by an upstream retreat to higher, cooler sites as water temperatures increased and glacial masses decreased.”

At some point, the western glacier stonefly will run out of mountain as the population searches for higher and higher sanctuaries, and, left with no place to go, it may face extinction. Glacier National Park is still beautiful today, but it isn’t the same park that I visited nine years ago. In nine more years, will there still be a place within the park’s borders where the western glacier stonefly can feel at home?

An adult western glacier stonefly.

(Image by Joe Giersch/USGS)

Introducing mosquitofish

Western mosquitofish, small freshwater fish typically about two and a half inches long, have been distributed far and wide from their native habitat in the southern U.S. and northern Mexico. Because they feed on insect larvae, including, depending on the circumstances, substantial numbers of immature mosquitoes (hence their name), humans have introduced them to waterways throughout the world.

In fact, these introductions are still occurring today – if you live in California’s Alameda County, you can request a delivery of mosquitofish right to your own pond.

Of course, biological controls rarely function exactly as intended. Mosquitofish are aggressive toward other fish, and have even been known to replace native fish species – which, in some cases, are more “efficient mosquito control agents” than the introduced mosquitofish that displaced them.

Mosquitofish also eat lots of other types of insects, as well as zooplankton and aquatic vegetation – meaning the effects of their eating habits can ripple outward from multiple parts of their food webs. Far from solely reducing mosquito populations, mosquitofish can cause big changes in their new homes (which is why some states regulate the expansion of their range).

Water bodies are not isolated from the environments that surround them – scientists call the flow of nutrients and resources between aquatic and terrestrial areas a ‘boomerang flux’ or ‘reciprocal subsidy.’ For example, many aquatic insects (including mosquitoes) spend their larval stages underwater, and later emerge as winged adults – the energy they incorporate into their bodies from the aquatic environment is transferred to terrestrial environments when those adults are eaten by predators like spiders or birds. New research recently published in the journal Freshwater Science suggests that introduced mosquitofish can alter that transfer of energy.

A team of scientists working at Utah’s Fish Springs National Wildlife Refuge, a series of spring-fed wetlands in the middle of the desert 125 miles southwest of Salt Lake City, measured how well aquatic insects survive to adulthood in the presence of western mosquitofish, as well as two native fish species.

The researchers set up experimental tubs of spring-water, complete with sediment and aquatic vegetation, to which they added either one species of fish or a combination (they also kept fish out of some of the tubs, so they could compare the results from the fish-filled tubs to the fish-less ones). Then they captured the adult aquatic insects that emerged from the tubs’ water surface – presumably the insects that did not survive their underwater larval stages became fish food. (None of the adult insects they collected were mosquitoes.)

The scientists found that the biomass of aquatic insects that emerged unscathed from the tubs that didn’t contain any mosquitofish was much larger than the biomass captured above the tubs where they were present: about 70 percent of the insect biomass made it out of the tubs containing native fish species, while only about 40 percent survived the mosquitofish tubs.

As the researchers note in their paper, “[w]estern mosquitofish have the potential to negatively affect the flow of energy from springs to the terrestrial environment,” in the form of reduced adult insect biomass. Though we humans may cheer when those adult insects are mosquitoes, we should remember that mosquitoes are not the only insects western mosquitofish consume, and the effects of introducing the fish to new locations are rarely as straightforward as we might like.

Western mosquitofish are often intentionally introduced to ponds and lakes in an effort to reduce mosquito populations; such introductions can have unanticipated negative consequences. 

(Image by NOZO via Wikimedia Commons/Creative Commons license)


“Silent Spring,” writer and ecologist Rachel Carson’s most famous work, focuses on a discussion of the detrimental effects of chemical pesticides on the environment, and on humanity. The book was published in 1962, but the issue of contaminants reverberating throughout the ecosystem is still pertinent today; though Carson’s writing inspired reforms, the problems she exposed are far from solved.

The authors of a study recently published in the journal Ecological Applications consider Carson’s seminal work relevant enough to cite it in the opening of their paper, an investigation of the pathways that mercury can take as it moves through a food web spanning an ecosystem that includes both aquatic and terrestrial organisms. (‘Boundaries’ between aquatic and terrestrial areas are often permeable to a reciprocal flow of food and energy resources.)

Mercury, a toxic heavy metal, is produced by both natural and anthropogenic sources; in aquatic environments, it’s easily converted to a bioavailable form that humans and other organisms can absorb, methyl mercury. Methyl mercury can reach high levels in predators like large fish as it biomagnifies, or bioaccumulates, instead of dissolving or metabolizing – as organisms consume contaminated prey, methyl mercury builds up in their flesh.

The scientists measured the methyl mercury concentrations of several species of terrestrial spiders, insects, and mites (all types of arthropods) around two Icelandic lakes; because of bioaccumulation, they expected the organisms that fed predominantly on aquatic food sources, which contain elevated methyl mercury levels, to display higher contamination levels than organisms that consumed terrestrial foods.

What they found instead was the opposite – arthropods that had an aquatic-based diet had much lower concentrations of methyl mercury in their bodies than those that ate terrestrial foods. The arthropods collected within a few feet of the lake with a large population of midges – an aquatic insect that was a likely food source for the spiders, insects, and mites – contained, on average, less than half the amount of methyl mercury found in arthropods collected far from the lake (and therefore, presumably, far from an aquatic-based food source like the midges).

The researchers also found that arthropods with an aquatic diet were at the top of a shorter food web than those with a terrestrial diet; with fewer steps in the food web, the scientists hypothesize, there was less bioaccumulation of methyl mercury, creating what they termed a ‘trophic bypass.’ As they write in their paper, “direct consumption of aquatic inputs result[ed] in a trophic bypass that create[d] a shorter terrestrial food web and reduced biomagnification of [methyl mercury] across the food web.”

The findings of this study were unexpected, and contrary to other research that revealed higher levels of terrestrial contamination in areas adjacent to polluted streams; as the authors of the study write, “our research highlights the fact that we still know little about the potential implications of [aquatic-terrestrial] linkages for terrestrial food webs and ecosystems, particularly with regard to societally important applied issues such as contaminant bioaccumulation.”

Contaminants and pollutants in the environment are a perennial problem; a problem that, in some ways, is just as obscure as it was more than half a century ago, when Rachel Carson first brought it to the attention of the public with “Silent Spring.”

Rachel Carson and colleague Bob Hines collecting marine samples in Florida in 1952.

(Image by U.S. Fish & Wildlife Service via USFWS National Digital Library)

Seeds, pits, and eggs

When I think of biological dispersal, the first few examples that come to mind all involve plants and seeds – the white puff of a dandelion head scattered by a gust of wind (based on the main photograph illustrating the Wikipedia page on dispersal, I’m not the only one who thinks of dandelions first); cherry pits spread far and wide by the lucky birds who found a tree laden with ripe fruit; even the squash plants sprouting from seeds tossed in a backyard compost pile.

But many organisms, animals as well as plants, disperse themselves, or are dispersed by the environment in which they find themselves: wind, or water, or humans move them around.

A team of Japanese researchers recently published a study in the journal Ecological Research detailing the dispersal of a particular type of coastal stick insect found in Japan and Taiwan, Megacrania tsudai, also known as Tsuda’s giant stick insect. Members of the genus Megacrania are large insects, usually between four and five-and-a-half inches long as adults. Only female Megacrania tsudai are found in the wild – they reproduce via parthenogenesis, an asexual process during which the young develop from unfertilized eggs. Megacrania tsudai eggs look like tiny, brown potatoes (pdf), the right size and shape for a dollhouse dinner plate, and adult females lay them often – the insects the scientists studied typically produced one egg per day.

The researchers were interested in whether or not Megacrania tsudai eggs, which are buoyant in seawater, can survive extended periods of time in the ocean – as a coastal species, they suspected that the insect might use ocean currents as a means of dispersal. They found that even after over a year spent floating in seawater, eggs hatched at the same rate as unexposed eggs (about 60% of the eggs eventually hatched, regardless of how long they had been in the water).

They also found that prolonged exposure to seawater delayed development – eggs not exposed to seawater began hatching after 120 days, while those floating in seawater for over a year didn’t begin hatching in substantial numbers until after 150 days, and some eggs were still in a pre-hatch development phase after 200 days.

In their paper, the scientists discuss the dangers Megacrania tsudai larvae and adults face as a terrestrial species living in coastal areas that regularly experience typhoons, strong winds, and floods. “However,” they write, “one or a few M. tsudai eggs are laid every day, and these eggs possess seawater tolerance and have a high variation in egg period duration. All of these characteristics are advantageous for an insect species living in a coastal forest habitat. Therefore, even if adults and larvae are completely lost due to natural disturbances, the eggs are an effective means of recovering and maintaining their population since they hatch normally after seawater exposure[.]”

Dispersal is an important way for populations to endure in the face of challenging local conditions. Megacrania tsudai eggs, just like dandelion seeds and cherry pits, can survive voyages beyond the realm of possibility for their progenitors.

Adult Megacrania tsudai on screw pine leaves in Taiwan; screw pine leaves are a primary food source for the insect. 

(Image by Bettaman via Flickr)