10/10/2021 at 12:32 CEST
Just a few days ago, on September 16, the Arctic sea ice reached its minimum annual extent of 4.72 million square kilometers. It was the twelfth smallest extension in 43 years. AND the 15 weakest extensions were recorded in the last 15 years. Among the many consequences of this situation, it emerges that endangers the future of seabird populations around the North Pole, most of which feed preferentially on fish and crustaceans on the edges of the frozen surface.
A study by the Institut de Ciències del Mar (ICM-CSIC) in Barcelona and the Norwegian Polar Institute (NPI) found that the menace loom the Arctic seabirds.
The research, published in the trade journal ‘Diversity and Distributions’, assesses the relationship between the retreat of the sea ice in recent decades and the declining arctic seabird populations. And bring some of the few empirical evidence that link changes in the cryosphere – the part of the Earth’s system where water is in solid form – with population dynamics of large predators in the North Pole.
One of the consequences of climate change is that the Arctic is warming faster than any other region on Earth (twice the global average), which caused dramatic environmental changes. Among others, a very rapid and pronounced reduction in ice extent, thickness and seasonal duration. Scientists fear that this situation has “profound effects on Arctic fauna and ecosystems”, in particular birds, explains NPI researcher Sébastien Descamps.
Declining bird colonies
Declining bird colonies“Since the responses of populations of arctic organisms to the lack of sea ice are not always straightforward, as different species and populations tend to respond differently, studies like this one are essential to understanding the impact its loss in arctic ecosystems & rdquor;, adds the scientist.
The research was carried out in the Norwegian archipelago of Svalbard, in the Arctic Ocean. The scientists used long-term time series data (1988-2018) from two fjords in western Spitsbergen and two of the most common seabirds in the Arctic, the Thick-billed Murre (Uria lomvia) and the white-legged gull (Rissa tridactyla).
Scientists have discovered that murre and gull colonies have declined in size in Svalbard since the mid-1990s. But the shapes of these trajectories are not linear and the size of gull colonies has stabilized or even increased in recent years.
Also in the survival of Common Murre chicks (Cepphus grylle mandtii) and in the feeding behavior of the ringed seal (Phoca hispida)
On the contrary, they were observed the positive effects the disappearance of sea ice in species considered to be dependent on ice. For example, improving the body condition of the Greenland whale (Balaena mysticetus).
The researchers point out in the study the “clear need & rdquor; additional studies to provide more information on how other species and communities respond to the retreat of sea ice. For example, if you influence the population size of polar bears (Ursus maritimus).
Low availability of food
Low availability of foodThe concentration of sea ice west of Spitsbergen decreased during the study period. AND sea ice concentration was significantly associated with seabird colony size with a two-year delay.
The link between sea ice and seabird population size is linked to changes in the food chain. Two years after a marked reduction in sea ice area, food availability is low.
And it is that sea ice can affect vertebrate populations by different mechanisms. Most of them are related to the availability of prey, at least for predatory species like seabirds.
Melting ice affects the probability of reproduction and, therefore, the size of the bird colony. This was the case in the two fjords studied in the case of murres. In the case of the seagulls, on the other hand, it was not evident in one of the fjords.
The authors note that the presence of glaciers releasing large volumes of meltwater can create “profitable feeding grounds”. Also “power hot spots & rdquor; that cushion the effects of the change on surface feeding birds, such as seagulls.
“Our study provides evidence that the continuing decline of the Arctic sea ice plays a (important) role in the trajectories of seabird populations”, conclude the researchers, including the Spaniard Francisco Ramírez. “However, the disappearance of sea ice in the breeding areas was probably not the main driver of changes in seabird populations,” they add.
Less ice, fewer birds
Less ice, fewer birdsThey predict that the predictable decrease in the extent or concentration of sea ice due to climate change will negatively affect predatory species that primarily depend on this habitat for food. The effects could be delayed in time.
« Less sea ice can result in lower productivity of plankton or fish. Which may mean less abundance (of seabirds) a few years later. And less survival and / or reproduction of their predators & rdquor ;, specifies the study.
But there will also be “direct and immediate & rdquor; on specific traits of predators (eg, foraging efficiency). Scientists fear this may happen, for example, with the Antarctic Adélie penguin (Pygoscelis adeliae).
But the occasional loss of ice this year is only part of the problem. Because the amount of ice over several years (that which has survived at least one summer thaw season) is currently one of the lowest levels since records began in 1984.
In addition, global warming has caused notable climate changes in Svalbard. Between 1970 and 2020, the average temperature increased by 4 ° C and in winter by 7 ° C. Temperatures above 20ºC are starting to be recorded. Scientists predict a temperature rise of 7-10 ° C in Svalbard by the end of this century.
Meanwhile, on the other side of the planet, In Antarctica, the extent of sea ice is also shrinking rapidly this year. However, it is still too early to determine if it has peaked.
Benchmark study: https://onlinelibrary.wiley.com/doi/full/10.1111/ddi.13389
You may be interested in: Towards an ice-free North Pole?
Main photo: Franco Banfi