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.

Krill Contribute to Ocean Carbon Storage in Patagonia

Waters in the sub-Antarctic region of Chilean Patagonia are fed by glaciers in one of the largest freshwater systems on Earth, the North and South Patagonian Icefields. A recent study published in Marine Ecology Progress Series found that Euphasia vallentini, the most abundant species of krill in Chilean Patagonian waters, play a key role in food webs. The study also discovered that this species of krill helps to sequester carbon in the oceansthey consume plankton, which take in carbon during photosynthesis, and discharge some of the carbon into deeper ocean waters through the production of fast-sinking fecal pellets. This is increasingly important as atmospheric carbon concentrations rise, as it contributes to the role of the oceans as a carbon sink.

The North Patagonian Icefield (Source: McKay Savage / Creative Commons).
The North Patagonian Icefield (Source: McKay Savage/Creative Commons).

Krill are small, shrimp-like crustaceans that are found in all of the world’s oceans. In an interview with GlacierHub, Humberto E. González, the lead author of the study from the Austral University of Chile, explained that krill form “a trophic [related to food and nutrition] bridge between the microbial community [bacteria, nanoplankton, microzooplankton] and the upper trophic layers [seals, whales, penguins, etc.]. Thus, they play a pivotal role in trophic flows.”

The study by González et al. focused on the region between the Magellan Strait and Cape Horn because of the unique biological, chemical and physical conditions created by the hydrological input from three different sources: nutrient-rich Pacific and Atlantic Sub-Antarctic Waters (waters that lie between 46°– 60° south of the Equator), and cold and nutrient depleted freshwater from Patagonian rivers and glaciers.

Waters that are more saline or that are colder have higher densities. However, as explained in the study, the effect of salinity exceeds the effect of temperature on density within this region, giving rise to strong saline stratification in the mixture of oceanic and freshwater terrestrial environments. This reduces the movement of important species between the benthic (the lowest level) and pelagic (open water) ecosystems in southern Patagonia.

The stratification also reduces upward and downward mixing of ocean water. This reduces carbon fluxes in the region, as the transport of carbon dioxide to deeper parts of the ocean through diffusion across layers occurs more slowly than the circulation of ocean waters with different carbon dioxide concentrations.

A map of the Strait of Magellan and the region where the study took place (Source: / Creative Commons).
A map of the region where the study took place. The icefields are located further north (Source: Creative Commons).

The team of scientists embarked on a research cruise in the region in October and November 2010, collecting chemical and biological samples at about forty different stations. Using a variety of techniques, they studied features such as the types and distribution of organic carbon in the waters, and the abundance and diet of E. vallentini. All this was done to better understand the role of E. vallentini in the region’s food web structures and in the transport of carbon to deeper layers of the ocean despite strong stratification.

In conversation with GlacierHub, González stated that “the species of the genus Euphausia (a functional group of zooplankton) play a paramount role in many disparate environments from high to low latitude ecosystems. Euphausia superba in the Southern Ocean and Euphausia mucronata in the Humboldt Current System are some examples.In this study, González et al. found that E. vallentini play a similarly important role in Southern Chilean Patagonia, consuming a range of plankton from nano- to phytoplankton and forming the dominant prey of several fish, penguin and whale species.

Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils / Creative Commons)
Krill, such as E. vallentini, form an important link in food chains between phytoplankton and larger animals (Source: Uwe Kils/Creative Commons)

The study also found that E. vallentini play an important role in passive fluxes of carbon through the sequestration of carbon in fast-sinking fecal pellets, or poop. The plankton ingested by E. vallentini takes in carbon dioxide during photosynthesis, and about a quarter of the plankton ingested by E. vallentini is then passed out in fecal matter. These fecal pellets form the dominant component of particulate organic carbon (organic carbon particles that are larger than a certain size) fluxes in the region’s waters, helping to sequester carbon as they sink to the ocean floor.

This process is accelerated by E. vallentini’s vertical diurnal migrations, which occur despite the strong saline stratification of waters in southern Patagonia. Their vertical movements, from deeper parts of the ocean during the day to the surface of the ocean in search of food at night, occurs more quickly than the rate at which their fecal pellets sink, speeding up the transport of carbon to deeper ocean layers. As González explained, “the Patagonian krill [and] the squat lobster (Munida gregaria) are the main species responsible for the carbon export towards deeper layer of the fjords and channels (in southern Patagonia).”

Although scientists from the Commission for the Conservation of Antarctic Marine Living Resources estimate that the total weight of Antarctic krill exceeds that of humans on Earth, they may not be immune from the effects of anthropogenic climate change. Indeed, González stated that a greater input of freshwater to the ocean could reduce nutrient levels in upper layers of the ocean. This will reduce the productivity of fjords and channels, reducing the availability of food for krill, and creating serious implications for the marine ecosystems that they are part of. This research serves as a reminder that biological organisms play an important role in the effects of marine ecosystems on the world’s climate, as they do in terrestrial ecosystems. 

Polar Ecology in Flux Due to Climate Change

Glacial melting and rising ocean temperatures are affecting the feeding, breeding and dispersion patterns of species, such as krill, cod, seals and  polar bears, in the polar regions, according to two recently published research articles. This climatic shift could create an imbalance in the regional ecology and negatively impact numerous species as the effects of climate change worsen.

The first article reflects on how a threat to a key species in Antarctica may shake up the food chain, while the other considers how a changing habitat in the Arctic could skew the population trends of several interconnected species and create a systemic imbalance in the ecosystem.

Glacier-originated melt-water creek carrying large amounts of particles. (Source: V. Fuentes/Nature)

After a nine-year study of krill in Potters Cove, a small section of King George Island off the coast of Antarctica, a team of South American and European marine biologists published their research this past June in the scientific journal Nature.

Krill are shrimp-like sea creatures that feed mostly on plankton.  Since they extract their food from the water by filtering it through fine combs, they are known as filter feeders.  Krill are found in all oceans and are an abundant food source for many marine organisms.  In the polar regions, predators such as whales often rely on krill as their only consistent food source.

The authors of this first piece found that a destruction of the krill population could extend undermine the Antarctic food web that relies on the presence of the small creatures.

 The study launched after stacks of dead krill washed ashore at Potters Cove in 2002, lining the coast. The article’s nine authors, Verónica Fuentes, Gastón Alurralde, Bettina Meyer, Gastón E. Aguirre, Antonio Canepa, Anne-Cathrin Wölfl, H. Christian Hass, Gabriela N. Williams and Irene R. Schloss, suggest the first observed  and subsequent stranding incidents are connected to large volumes of particulate matter dumped into the ocean by melting glaciers. The high level of tiny rock particles carried by the glacial melt water may have clogged the digestive system of filter feeders like krill.

The researchers conducted a series of experiments in which they exposed captive krill to water with varying amounts of particulates. The krill’s feeding, nutrient absorption and general performance were all significantly inhibited after 24 hours of exposure to concentrations of particles similar to those found in the plums of glacial runoff.

Stranded krill along the southern shore of Potters Cove, King George Island (Source: V. Fuentes/Nature).

Although krill are mobile creatures and can usually avoid harmful environments, exposure to the highly concentrated particles interfered with their ability to absorb nutrients from their food.  The krill became weak, which resulted in their inability to fight local ocean currents and their subsequent demise.

About 90 percent of King George Island is covered in glaciers that are melting and discharging particles into the surrounding marine ecosystem, according to the article.  Similarly, an overwhelming majority of the 244 glacier fronts, a location where a glacier meets the sea, studied on the West Antarctic Peninsula have retreated over the last several decades, which suggests that high particulate count from glacial meltwater may be occurring in other parts of Antarctica.

Since much of the Antarctic coast is not monitored and most dead krill sink to the bottom of the ocean, the authors caution that these stranding events likely represent a small fraction of the episodes.  

In another recent study on climate change’s impacts on wildlife, scientific researchers with the Norwegian Polar Institute focus their attention on the high Arctic archipelago of Svalbard, Norway.  They found that glacial melting and changes in sea ice have impacted numerous land and sea animals in the Arctic. These shifts have the potential to influence more creatures. The study, by Sebastien Descamps and his coauthors, was published this May in the scientific journal Global Change Biology.

Tidewater glacier in Greenland, taken from helicopter (Source: Brocken Inaglory/CC)

Some species, such as the pink-footed goose, are benefiting from the warming Arctic climate, however. Lower levels of spring snow cover and earlier melting has expanded the time for its breeding and the area of available breeding grounds, which will likely lead to an increase in the geese population.  

However, the success or the overpopulation of one species can cause an imbalance in the ecosystem and negatively affect numerous other organisms.  As the authors explain, “An extreme increase in a herbivore population [like the geese] has the potential to affect the state of Svalbard’s vegetation substantially, with possible cascading consequences for other herbivorous species and their associated predators.”

The authors conclude, “even though a few species are benefiting from a warming climate, most Arctic endemic species in Svalbard are experiencing negative consequences induced by the warming environment.”

Polar bears and the Arctic ringed seal are among the species which are suffering the impacts of a warming Arctic.  Seals breed on sea ice and depend on snow accumulation on the ice in order to form lairs for their pups.  The snow lairs provide protection from the harsh winter and predators.  As ocean temperature warms and the season of sea ice formation shortens, there is less time for accumulation of snow.  Thus, many seals are giving birth on bare ice, which leads to a much higher pup mortality rate.

Weddell seals (Source: changehali/CC).

This  article also points out that tidewater glaciers have become increasingly important foraging areas for several species, including seals, seabirds and whales.  Additionally, these creatures’ presence makes the glacier fronts fruitful hunting grounds for polar bears. Icebergs drifting near the glacier fronts create valuable resting areas in the hunting grounds for many of these animals.

The authors hypothesize that the increase in icebergs calved from the glacier fronts could counterbalance the ecological loss resulting from the disappearance of sea ice. Yet this may only offer a brief reprieve for the Arctic species that depend on the ice.  

“Continued warming is expected to reduce the number of tidewater glaciers and also the overall length of calving fronts around the Svalbard Archipelago.  Thus, these important foraging hotspots for Svalbard’s marine mammals and seabirds will gradually become fewer and will likely eventually disappear,” wrote the authors.

Taken together, these two recent articles show that glacier retreat, as well as other forms of loss of ice, have negative impacts on high-latitude ecosystems, both in the Arctic or in Antarctica. There are strong similarities between these two cases, distant from each other in spatial terms but close to each other in their shared vulnerabilities.