Roundup: Seals, Flood Mitigation, and Freezing Levels

Seal Whiskers Detect Ecosystem Change

From Polar Biology: “Warm Atlantic water in west Spitsbergen have led to an influx of more fish species. The most abundant marine mammal species in these fjords is the ringed seal. In this study, we used isotopic data from whiskers of two cohorts of adult ringed seals to determine whether signals of ecosystem changes were detectable in this top marine predator.”

Find out more about ringed seals here.

A ringed seal in Kongsfjorden, North West Spitsbergen (Source: The Might Fine Company/Google Images).

 

Flood Mitigation Strategies in Pakistan

From Natural Hazards: “The frequency and severity of flood events have been increased and have affected the livelihood and well-being of millions of people in Pakistan. Effective mitigation policies require an understanding of the impacts and local responses to extreme events, which is limited in Pakistan. This study revealed the adaptation measures adopted in Pakistan, and that the local policies on disaster management need to be improved to address the barriers to the adoption of advanced level adaptation measures.”

Find out more about flood risk mitigation in Pakistan here.

Pakistani villagers leaving their homes after a flood in Muridke (Source: DAWN/Google Images).

 

Rising Freezing Levels in Tropical Andes

From AGU Publications: “The mass balance of tropical glaciers in Peru is highly sensitive to a rise in the freezing level height (FLH). Knowledge of future changes in the FLH is crucial to estimating changes in glacier extents. Glaciers may continue shrinking considerably, and the consequences of vanishing glaciers are especially severe where people have only limited capacity to adapt to changes in the water availability due to, for instance, lack of financial resources.”

Find out more about freezing levels in Peru here.

Evidence of melting at Pastoruri glacier in Northern Peru (Source: Inyucho/Creative Commons).

 

Polar Bears and Ringed Seals: A Relationship in Transition

Disconnected sea-ice during the Svalbard summer (Source: Allan Hopkins/Creative Commons).

Along the tidal glacier fronts of Svalbard, an archipelago halfway between Norway and the North Pole, polar bears have changed their hunting practices. A recent study published in the Journal of Animal Ecology indicates the new behavior is a response to rapidly disappearing sea ice. Charmain Hamilton and other researchers from the Norwegian Polar Institute mapped changes in the spatial overlap between coastal polar bears and their primary prey, ringed seals, to better understand how the bears are responding to climate change. The results don’t bode well for the long-term survival of polar bear populations: as sea ice continues to shrink in area, ringed seals—calorie-rich prey that are high in fat— have become increasingly difficult to catch during the summer and autumn. The bears are now finding sources of sustenance elsewhere: in the archipelago’s thriving bird colonies.

The Arctic is warming at a rate three times the global average, and the sea ice in the Svalbard region is experiencing a faster rate of decline than in other Arctic areas. As Charmain Hamilton reported in an interview with GlacierHub, the findings could demonstrate what the future holds for the top predator elsewhere. “The changes that we are currently seeing in Svalbard are likely to spread to other Arctic areas over the coming decades,” she said.

A polar bear steps across a gap in the sea ice near Spitsbergen, Svalbard (Source: Thomas Nilsen/The Barents Observer).

Svalbard’s polar bears exhibit one of two annual movement patterns: some follow the sea ice as it retreats northward during the summer, while others stay local, inhabiting coastal areas throughout the year. Both groups of bears depend on sea ice as a platform to hunt ringed seals. Given a rapid decline of sea-ice levels that began in 2006, Hamilton and other researchers wanted to know if the coastal bears were still hunting ringed seals under the deteriorating conditions.

The researchers compared satellite tracking data for both polar bears and ringed seals from the periods 2002-2004 and 2010-2013 to assess whether the predator-prey dynamic had shifted. The data was analyzed according to season, with researchers paying careful attention to the dynamics of spring, summer and autumn.

In spring, access to fat-rich ringed seals is critical, particularly for mothers weakened from nourishing their young in winter dens. The study shows that coastal polar bears continued to spend the same amount of time near tidal glacier fronts in spring as they did when sea ice was more abundant. The authors conclude that the declines in sea ice in Svalbard have not yet reached the stage at which bears must find alternative hunting methods during the spring. This could help to explain why cub production is not currently declining.

A calving glacier in Svalbard (Source: Geir Wing Gabrielsen/Norwegian Polar Institute).

However, during summer and autumn, bears are spending less time in the areas around tidal glacier fronts. The study shows a significant decrease in the amount of time bears spent within 5 km of glacier fronts and a sharp increase in the distances they traveled in search of food per day. The ringed seals, on the other hand, have remained near the glacier fronts. As Hamilton reported to GlacierHub, “The reduced spatial overlap between polar bears and ringed seals during the summer indicates that the reductions in sea ice have made it much more difficult for polar bears to hunt their primary prey during this season.”

As sea ice recedes, ringed seals are increasingly relying on calved pieces of glacier ice as shelters and resting places. Since these pieces of calved ice are no longer connected to land-fast ice, polar bears can no longer walk up to the seals or wait by their breathing holes, but have to attack from the water. This involves swimming surreptitiously up to seals resting on calved glacier ice and bursting onto the platform to make a kill. But this specialty hunting technique has only been observed in a minority of bears.

A Svalbard polar bear eats a ringed seal on a calved piece of glacier ice (Source: Kit Kovacs and Christian Lydersen/Norwegian Polar Institute).

So where are the coastal bears getting their calories during summer and autumn? The study shows that along with the marked decline in sea ice, the coastal bears were spending more of their time around ground-nesting bird colonies. At present, these tactics seem to be working. The bears are benefiting from a large increase in the populations of several avian species in the region, which Hamilton attributes to ongoing international conservation efforts along migration routes. While an increase in the amount of time polar bears spend on land is considered a cause of deteriorating health in other bear populations, the adult bears and cubs of Svalbard have not shown marked signs of decline.

Have the bears found a lasting alternative? Jon Aars, a research scientist and one of the co-authors on the paper, doesn’t think so. In an interview with GlacierHub, Aars emphasized that while birds and eggs provide the bears with an alternative to burning fat reserves as they wait for the sea ice to return, the dynamic is not permanent. “It is not likely that switching to eating more birds and eggs is something that can save polar bears in the long run if sea ice is gone for the whole of, or most of, the year,” he said. “We do think the bears are still dependent on seals to build up sufficient fat reserves. And it is limited how many bears can utilize a restricted source of eggs and birds on the islands.”

A mother and her cubs look out across an ice-free stretch of bay as they hunt for birds and eggs (Source: Thomas Nilsen/The Barents Observer).

The bears have adapted to the current change in their environment but may not be able to adapt as well in the future. The authors of the paper point out that the increased rates of movement required to hunt avian prey increases the bears’ energy needs. Additionally, as more bears rely on avian prey, their high rate of predation means that bird populations on the archipelago will likely decline, causing bears to alter their hunting strategies again. Ringed seals have not changed their own spatial practices, and the authors propose that more bears could learn, or be forced to learn, the aquatic hunting method.

However, ringed seal populations are in decline due to the loss of sea ice, according to Hamilton. Thus, the future of both species in the region is uncertain. In sensitive environments like the Arctic, predator-prey dynamics are fragile, particularly for species of such high trophic positions. In the future, Hamilton would like to include other Arctic marine top predators in similar studies to better understand how Arctic marine mammal communities are being impacted.

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.