Are Melting Glaciers Putting Arctic Fish at Risk?

Shifts in Capelin Fish Feeding Ecology

An important Arctic fish might be in trouble. A recent study in Greenland examines changes in the feeding ecology of capelin, a small forage fish in the smelt family. Melting glaciers are affecting its diet, and this change in diet can heavily influence its growth and reproduction. This could spell trouble for the other animals that eat capelin.

Found in the Arctic, Capelin are an important food source for marine mammals such as whales and seals. Atlantic cod, a major commercial fish species, are one of its major predators. Atlantic puffin also like to feed on them, along with other sea birds.

A puffin enjoying a mouthful of what appears to be capelin (Source: Lawrence OP/Flickr).

Capelin enjoy feeding on plankton, microorganisms that float in the sea and on freshwater. Krill, small shrimp-like crustacean, are also crucial in the diet. Capelin seem to migrate less than other species, making them extremely dependent on the food that’s readily available to them. Any major changes in food availability can ripple through the Arctic food web.

The Godthåbsfjord in West Greenland was sampled at a number of sites, all the way from the mouth where it opens to the ocean to the furthest inland basin. Capelin were sampled by the researchers during the months of May and August, when increased meltwater from summer heating flows into the fjord. The fish were then divided into 2-cm interval size groups, assessing for differences in age. Researchers carefully dissected the stomachs and intestines, preserving them so that they could later examine their contents to determine diets over different locations and times.

Lorenz Meire talks about the framework of the study in an interview with GlacierHub. Meire is a marine scientist at the Royal Netherlands Institute for Science Research and one of the scientists behind this study. “By trawling in a sub-Arctic fjord impacted by glacial meltwater, we aimed to assess the change in capelin size distribution and its diet throughout the season,” he says. Meire adds that scientists tried to link diet with observed changes in zooplankton biomass and environmental conditions.

Three small capelin on tin foil (Source: Rodrigo Sala/Flickr).

What are some observed environmental changes?

Studies show a shift in abundance of krill from freshwater-influenced regions toward the oceans. We see similar shifts with large plankton. GlacierHub spoke with Kristine Engel Arendt, a marine biologist from the University of Copenhagen. Her research on plankton community structure is referenced in the study. She provides some insight on how runoff from the exit glacier and high up ice sheets affect the ecosystem ecology, looking particularly at smaller plankton species.

Arendt told GlacierHub that the fjord typically experiences a bloom of algae in the spring, which is a food source for plankton. The addition of freshwater from the late summer runoff initiates a second bloom of algae, driven by an upwelling of nutrients. “The marine food web is closely linked to the energy source from the algae bloom, and therefore zooplankton species that can utilize food over the entire summer period are favored,” she says. These smaller species of plankton benefit from the nutrients. They use this extra algae bloom during the summer to grow and reproduce. This observation indicates an abundance of smaller plankton at the inner basin region in August. Stomach examinations show a clear increase of small plankton in the diet of fish from this area of the fjord.

Drifting Ice, Godthåbsfjord, West Greenland (Source: Lorenz Meire).

Arendt points out that climate change effects such as melting glaciers are not always negative. We see that this inflow of freshwater is in fact beneficial to these smaller plankton. But how might this change affect capelin?

A Disadvantage to Younger Capelin

It’s important to look at the migration and reproductive pattern of capelin to understand the impacts. Maturing adult capelin spawn from April to June in the fjord, from the inner basin to near-coastal regions. Studies show that all male capelin and some females die off with connection to spawning. Researchers can then presume that the May sample will consist of both mature and immature capelin, and August will be dominated by young capelin. This is reflected in the findings of the study.

The beautiful fjords of Greenland (Source: GlacierHub author Arley Titzler)

The quality of the available food sources must also be examined. It differs with plankton size. Larger plankton species are relatively richer in fat per unit of weight. This makes them more ideal for energy intake and growth than the smaller plankton species. Energy intake and growth is particularly critical for young capelin. Meire told GlacierHub, “If smaller copepods (plankton) become more abundant, they will form a more important food source for capelin. Though this can impact the energy transfer as small copepods in the diet cannot compensate for the absence of larger copepods and krill.”

Lack of the more favored species in the inner regions can negatively affect nutrition of capelin. Younger capelin here are at risk. They will need to feed on the larger, fat-rich plankton to receive enough nutrients to effectively grow and reproduce. This can greatly affect the Arctic food web.

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Study shows glacial melting changes mountain lake ecology

In the Rocky Mountains, researchers have been studying a pair of lakes–Jasper and Albino. While they are similar in size, location, and depth, there is one important difference: Jasper Lake is fed by glacier meltwater while Albino Lake is fed by snow. A report published in May reveals that this small difference has had a dramatic impact on the biology and chemistry of the lake itself, indicating that water source plays a much larger role in the ecological health of mountain lakes than previously thought.

Hallett Peak, Rocky Mountain National Park (source: NPS)
Hallett Peak, Rocky Mountain National Park (source: NPS)

Mountain lakes are an important source of regional water in the western United States, and are known for their historically high levels of biodiversity. Recently, these lakes have seen rapid changes which sparked concern from the scientific community. Last month the California-based Consortium for Integrated Climate Research in Western Mountains (CIRMOUNT) addressed the need for research on mountain lakes by publishing a special feature of Mountain Views, their biannual report compiling recent research on western United States mountains, that focuses exclusively on mountain lakes. The ten featured research articles all point to the importance of alpine lake conservation and investigate the impacts of climate change and other anthropogenic influences on regional ecology and environmental health.

One article— “Effects of Glacier Meltwater on the Algal Sedimentary Record of an Alpine Lake in the Central U.S. Rocky Mountains”— studied glacier-fed and snow-fed lakes and found drastic differences in the chemical compositions and species ecology between the two. The researchers, Krista Slemmons of the University of Wisconsin, Stevens Point, and Jasmine Saros of the University of Maine chose two alpine lakes in the Beartooth Mountains, Jasper and Albino, which are physically and geographically similar. However, Jasper Lake is fed by a glacier meltwater, while Albino Lake is only fed by snowmelt.

core samples (wiki)
core samples (wiki)

To determine differences in the lakes’ histories, sediment cores were taken from the bottom of the Jasper and Albino. Over time, organisms and nutrients accumulate on the lakebed and gradually build up as sediment in bodies of water. The layers of the core therefore tell a story about the history of the life within the lakes. By analyzing the sediment cores, the researchers were able to look back through time and see how the type of water feeding the lakes has led to differences in life history and biogeochemical cycling.

Within the Jasper core, researchers found high levels of plankton species that thrive in high nitrogen conditions, indicating that the lake has had higher nitrogen levels than Albino Lake over the past 3,000 years, with particularly high levels corresponding to periods of high glacial melting, most notably the 20th century.

fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)
fresh-water phytoplankton, used to determine historic water ecology and nutrient levels (wiki)

Today, glacier-fed Jasper Lake has approximately 63 times more nitrogen than snow-fed Albino Lake. It is the high concentrations of nitrogen in the glacial meltwater that has led to the differences between the lakes. This trend will continue as glacier melting accelerates with climbing temperatures.

While nitrogen is an important nutrient, and often limited in alpine lakes, it is possible to have too much of a good thing. In Jasper Lake, the sediment cores also indicated that species richness, or the number of different types of species present in an ecosystem, was lower than in the nitrogen-limited Albino Lake. These findings suggest that a high influx of glacial meltwater into lakes may lead to eutrophication.

algal bloom from eutrophication (flickr)
algal bloom from eutrophication (flickr)

Eutrophication is a type of water pollution that occurs when high levels of nitrogen cause plant and algae to grow excessively. This phenomenon, known as an algal bloom, blocks sunlight from penetrating the water column, decreases the oxygen levels in the water, and can harm other species in the ecosystem. Eutrophication is most commonly seen as a result of nitrogen fertilizer runoff into bodies of water, but the nitrogen stored in glacier ice appears to have high enough concentrations to cause the same negative impacts.

While global water scarcity is enough cause for concern over glacier retreat, these findings suggest that glacier melt has wider reaching negative impacts on ecosystem function than previously recognized. Understanding the cascade of environmental impacts resulting from glacial melting will become increasingly important as temperature rise continues to break global records, and will play an important role in preserving the biodiversity of marine ecosystems.

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Roundup: Kelp, Firn, and Plankton Studied in Svalbard

Each week, we highlight three stories from the forefront of glacier news.

Warming of Artic  Changes Kelp Forests’ Density and Depth

From Polar Biology:

Kelp Seaweed. Courtesy of Flickr User snickclunk.
Kelp Seaweed. Courtesy of Flickr User snickclunk.

“Arctic West Spitsbergen in Svalbard is currently experiencing gradual warming due to climate change showing decreased landfast sea-ice and increased sedimentation. In order to document possible changes in 2012–2014, we partially repeated a quantitative diving study from 1996 to 1998 in the kelp forest at Hansneset, Kongsfjorden, along a depth gradient between 0 and 15 m. The seaweed biomass increased between 1996/1998 and 2012/2013 with peak in kelp biomass shifted to shallower depth, from 5 to 2.5 m.”

Read more about this study here.

 

Firn, Newly-Settled Snow on Glaciers, Stores Water

Firn, courtesy of Flickr User Alpen Picasso.
Firn, courtesy of Flickr User Alpen Picasso.

From  Geophysical Research Letters:

“Ice-penetrating radar and GPS observations reveal a perennial firn aquifer (PFA) on a Svalbard ice field, similar to those recently discovered in southeastern Greenland. A bright, widespread radar reflector separates relatively dry and water-saturated firn…Our observations indicate that PFAs respond rapidly (subannually) to surface forcing, and are capable of providing significant input to the englacial hydrology system.”

Read more about this study on firn hydrology here.

 

Krill and Crustaceans Play Bigger Role in Warming Ecosystem

From Polar Biology:

Polar Cod, which relies on plankton, being dried in Norway. Courtesy of Flickr User Victor Velez.
Polar Cod, which relies on plankton, being dried in Norway. Courtesy of Flickr User Victor Velez.

“Euphausiid (krill) and amphipod dynamics were studied during 2006–2011 by use of plankton nets in Kongsfjorden (79°N) and adjacent waters, also including limited sampling in Isfjorden (78°N) and Rijpfjorden (80°N). The objectives of the study were to assess how variations in physical characteristics across fjord systems affect the distribution and abundance of euphausiids and amphipods and the potential for these macrozooplankton species to reproduce in these waters…Euphausiids and amphipods are major food of capelin (Mallotus villosus) and polar cod (Boreogadus saida), respectively, in this region, and changes in prey abundance will likely have an impact on the feeding dynamics of these important fish species”

Learn more about these ecosystems here.

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Glacial Runoff: Bane or Boon for Aquatic Life?

As glaciers melt around the world, their waters carry high concentrations of sediments into glacial lakes and rivers. That glacial sediment brings some nutrients into the lakes, but also blocks sunlight– the energy source which organisms need to survive.

In a recently published paper in The Journal of Plankton Research, titled When glaciers and ice sheets melt: consequences for planktonic organisms, Dr. Ruben Sommaruga of  the University of Innsbruck, Austria, analyzed the relationship between sunlight, nutrients and organisms.

Glacial rivers and lakes often appear blue because of the particular mix of minerals and sediments, known as glacial flour, or glacial milk, that gets scraped up when glaciers expand and grind the bedrock surface over which they move. Glacial retreat releases that glacial flour into rivers and lakes at unprecedented rates. At the same time, new glacial lakes and rivers are forming, providing scientists with an opportunity to observe if and how life will thrive in these bodies of water.

Figure of turbid glacial lakes transitioning to clear oligotrophic lakes.
Figure of turbid glacial lakes transitioning to clear oligotrophic lakes. Figure by RUBEN SOMMARUGA 2015

High concentrations of glacial flour in young glacial lakes makes them  turbid, or cloudy, blocking sunlight. These lakes become clearer as they age, as glacial flour settles to the lakebed. This process increases sunlight penetration in the water. Combined with an increase in other forms of nutrients entering the lake over time, such as bird droppings, this process results in a clear blue glacial lake with a healthy ecosystem. These clear lakes, called oligotrophic lakes, can support plankton and small fish, but do not have many aquatic plants. Eventually, if nutrients keep increasing in oligotrophic lakes, they can develop into highly biologically active lakes, called eutrophic lakes, with abundant aquatic flora and fauna.

An image of Kurtkowiec Lake, an oligotrophic lake in the Tatra Mountains of southern Poland.
Kurtkowiec Lake, an oligotrophic lake in the Tatra Mountains of southern Poland, via Wikipedia.
An image of Lake Waahi, a eutrophic lake in Huntly, New Zealand.
Lake Waahi, a eutrophic lake in Huntly, New Zealand, via Flicker.

In order for this eutrophication to occur, organisms at the base of the food chain, particularly  plankton, need to survive in the water during its early phase with low sunlight penetration.

Once a lake loses its connection with its original glacier, either because the glacier completely melted or because its runoff ceased, it changes more rapidly from a cloudy glacial lake to a clear oligotrophic lake. The location and size of the lake and glacier influence the pace of this process and the potential for eutrophication.

Research on these processes–which integrate climatic, hydrological, chemical and biological components–contributes to a more general understanding of the ecological consequences of climate change.

In the article, Dr. Sommaruga states “ . . . estimates based on a scenario where all glacier ice disappears in the Swiss Alps, predict 500 new lakes, which represent 30% more lentic [stillwater] systems for Switzerland. In other regions, such as in northern Patagonia, total glacial lake area has increased by 65% from 1945 to 2011.”

This research shows that plankton and other small organisms survive, though not always thrive, in young cloudy glacial lakes and rivers. Future research will extend current understanding of these ecosystems, and trace the implications for our planet’s freshwater ecosystems.

Other posts at GlacierHub have described glacial lakes in Switzerland and Greenland.

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