A melting world? Indirect impacts of sea ice loss

With the last post concentrated on the direct effects of sea ice loss in the Arctic, this post will look again at tithe phenomena of sea ice, but with a particular focus on the indirect impacts of Arctic sea ice disappearance. Below is a short video which aims to portray ice minimum volume from 1979 to 2013.

Sea ice loss may influence ecological dynamics indirectly through effects on species movements and disease transmission causing species to become more vulnerable. Arctic populations isolated when an ice free season occurs in the Arctic, the declining presence of sea ice could reduce inter-island migration. With the lengthening of the ice free season, genetic isolation among populations is encouraged (Post et al. 2013). For some species, sea ice can act as a barrier to dispersal, due to the lengthening of the sea ice free season will increase population mixing, reducing genetic differentiation. This impending loss of sea ice will increase contact among closely related series for which it currently acts as a mixing barrier. Hybridisation is likely to become increasingly common. Polar bears and grizzly bears may be the result of increasing inland presence of polar bears as a result of prolonged ice free seasons (Hoflinger, 2013).  In Canada, the projected decrease in sea ice cover with Arctic warming, will increase contact between Eastern and Western Arctic species.

Image of a 'pizzly' the grizzly-polar bear hybrid. 

A second indirect impact is changes that occur in animal behaviour as a result of sea ice loss. In the Canadian Arctic, later ice seasons and increased shipping traffic due to the lengthened ice free seasons could prevent migration of the Dolphin and Caribou (Poole et al. 2010). It is widely understood by ecologists that migration can decrease the likelihood of parasitism. The changes in ice formation within the Arctic could change the amount of parasite loads among the Dolphin migration herds. However, sea ice loss is not always looked on negatively, with the reduction of sea ice promotion migration hence preventing disease epidemics where the sea ice provides a corridor for pathogen transmission (Post et al. 2013).

Image. Caribou migration route in the Arctic. 

Sea ice loss also effects terrestrial ecosystems including especially, land adjacent to the sea ice. Arctic warming, delayed freeze season and sea ice loss will promote permafrost warming increasing terrestrial primary productivity. There has been increases in the abundance and cover of shrubs occurring across the Arctic. 

A recent report by the Arctic council and the National Oceanic and Atmospheric administration (2013) shows evidence of a shift to a new warmer, greener state. The major findings of this report include:

1) Vegetation in the Arctic is greener with a longer growing season. 

2) Wildlife and large land mammal populations continued declining trends with Caribou having unusually low numbers. 

3) Sea ice extent in September 2013 was the sixth lowest since observations began in 1979. 

4) Northward migration into the Arctic of fish such as Atlantic Mackerel and Atlantic Cod. 

This report shows that recently there has been increased concerns over this region of sea ice loss. With the academic community trying to understand how extensive the impacts of sea ice loss are. With conditions changing for many species in the Arctic, it is important to note that sea ice decline is not itself solely responsible for many individual species decline, however it plays a role with a combination of other factors. Declining sea ice is not uniform and therefore individual species responses will remain varied (Mueter and Litzow, 2007).

As we can see from the last two posts, sea ice loss can have both negative and positive effects on the ecological diversity of the Arctic. Keep your eyes peeled for the next post which will offer some insight into a completely different area of global biodiversity, one that is extremely threatened- freshwater biodiversity.


Score Board Update.

Anthropocene 4 - 3 Biodiversity 

Biodiversity in the cryosphere

As one of Earth's major biomes, the Cryosphere (taken from the Greek 'krios' meaning cold, frost or ice) is extremely important to consider when trying to understand global biodiversity. The Cryosphere encompasses those parts of the world which are frozen including, ice sheets, glaciers, frozen rivers, lakes, sea ice, permafrost and ice shelves. Today, I am focusing on the importance of sea ice to Arctic biodiversity after being fascinated by the paper published from Post et al (2013) introduced to me by my global environmental change lecture on the 6th December. With it being published only a few months ago, I decided to read the full paper and became instantly intrigued by polar biodiversity.

Sea ice compromises unique ecosystems in, on and under the ice. This habitat is critical for many species including vertebrates, diatoms, also terrestrial productivity and aquatic diversity. With 80% of the tundra in the Arctic lying within 100km of an sea ice covered ocean, Arctic ice loss driven from amplification Arctic warming is vital for ecological dynamics in this area (Post et al. 2013). Arctic amplification is the melting of ice due to a positive feedback albedo system. Ice has a high albedo therefore reflecting sunlight keeping the poles cool. However through ice melt, more of the Arctic ocean becomes exposed and due to oceans being darker they have a much lower albedo. This means they absorb heat warming the oceans and the atmosphere. As the oceans absorb heat, they also have to release this increased heat to enable the sea ice to form for the next year. Due to this feedback, the more ice loss the longer it takes for oceans to release the heat it has absorbed and therefore sea ice formation gets delayed. This can have affects for semi-aquatic species such as polar bears which use the sea ice for reproduction ground and for resting during long migration routes.

With anthropogenic warming Arctic sea ice extent has slowly been declining.

Source. A) Graph showing the declining annual minimum Arctic sea ice extent from 1979 to 2012. Although,  there is seasonal variability the overarching trend is a decline. B/C) Two maps showing the percentage concentration loss of sea ice with the scale bar showing -5% to 5% change. B is from 1979-1999 and C from 2000 -2011. 


The trend seen in the maps is showing percentage loss, especially around the edges of the sea ice, due to warming oceans.

The direct effects of Arctic sea ice loss

1. Primary producers depend on the sea ice habitat, underpinning the whole Arctic marine food web.

- With the loss of sea ice, this is a loss of habitat for algae and phytoplankton.  The timing of the algae bloom which is ultimately driven by light penetrating the ice when it is thin enough, is vital for the reproduction of zooplankton grazers. Disruption of this timing due to accelerated ice melt has created mismatches for zooplankton production timing and the consumers up the food chain.
- Earlier phytoplankton blooms can shorten the length for primary productivity consequently affecting the zooplankton production and the Arctic cod species that feed on them (Post et al. 2013).

2. With ice melt comes increasing freshness of the Arctic ocean.
- This reduces the nutrient availability for phytoplankton which limits their productivity despite increased solar penetration through ice thinning.

3. As previously touched upon, vertebrate species such as polar bears require sea ice for reproduction and resting and therefore they are directly implicated by sea ice thinning. One species also effected is the ringed seal (Gohring, 2012). More than two thirds of the Arctic has been estimated to have insufficient snow cover for ringed seals to reproduce challenging their whole survival. A ringed seal is currently under consideration for the threatened species list due to the way it builds caves to rear its offspring in snow drifts on sea ice (NOAA, 2013).  (Hezel et al. 2012) estimated that snow drifts must be at least 20cm deep to support the caves. As sea ice disappears, there is no where for the snow to pile up, ultimately declining the area where the seals can reproduce. What is also worrying is that with earlier snow melt year on year, the caves will melt also much earlier, leaving the young vulnerable to the outside conditions and predators.

Next week, I will be continuing the polar theme by exploring the indirect impacts of sea ice loss in the Arctic so keep those eyes peeled. Only two weeks till christmas!!

Score Board Update: Anthropocene 4 - 2 Biodiversity. 

Invader Intolerance: A presumptuous viewpoint?

As my introductory post touched upon, there are many anthropogenic impacts effecting biodiversity (see below for a comprehensive list!). 

- Habitat destruction and fragmentation

- Agricultural intensification and changes in land use

- Changes in forest management practices

- Overfishing

- Atmospheric pollution

- Water pollution

- Climate change

- Human disturbance

- Invasive species

- Harvesting and collection of species (hunting)

- Ocean acidification

(Natural England, 2011) 

The focus for today is invasive species. Before I start chattering on about zebra mussels and the red squirrel, I believe it is crucial to understand just how scientists define and quantify biodiversity. The term 'biodiversity' originates from conservation biology and was coined by Walter Rosen in 1985. A formal definition was published by the Convention of Biological Diversity (1992) which stated:

'Biodiversity is the variability among living organisms including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems'. 

Biodiversity measures have, however, also taken a battering over the years.  Wilson (1992) discussed the ambiguity surrounding measures of diversity and explored the possibility that biodiversity was in fact restricted by measuring species numbers alone. This has also been reiterated more recently by (McCann, 2007).  Nowadays there is still uncertainty when quantifying biodiversity (scientists can never make up their minds) and therefore this will be considered in much greater detail in a few weeks. 

So now back to the purpose of this post- 'INVASIVE SPECIES'. Although known worldwide as threatening and disruptive, non-native species and their impacts to biodiversity continue to be greatly debated throughout scientific literature. So why do invasive species have such a bad reputation? Invasive, known also as 'alien' and 'non- native' species can have significant effects on the existence of some species and their habitats. An example is the native red squirrel (Sciurus vulgaris) which has become threatened and outcompeted in the UK by the non-native 'grey' squirrel (Sciurus carolinensis). The first evidence of the red squirrel dates back to the end of the last ice age, 10,000 years ago. 

Save our native: The Red Squirrel

However, since the grey squirrel became introduced to the UK in the 19th Century it has replaced the red squirrel throughout most of England, Wales and parts of Scotland and Ireland (Bryce, 1997). The traditional explanation for this reduction in the red squirrel, is the overwhelming competition with the grey squirrel for food resources (Kenward and Holm, 1993). This was not the only reason for their gradual decline, another proposal is the introduction of devastation parapoxvirus (a fatal strand of squirrel "pox") that was brought from North America to the UK by the grey squirrel. The disease spread into the red squirrel population hence the rate of infection was extremely high. This induced a population crash, reducing the crowding pressures on non-native grey squirrels which subsequently increased in numbers (Gurnell et al. 2004). 

Squirrel distribution maps from 1945- 2010 showing the interaction between the red and grey squirrels (RSST, n/d). 

From the above maps, the red squirrel population can be seen to be rapidly declining especially in Northern England and Wales, with the grey squirrel taking over the South of England and the Eastern Coast of Wales. Wales and the the midlands, surprisingly, have habitats which are occupied by both species. From the maps above it is highlighted that urgent steps are needed to address the issue of invasive species in order to save native species. 

It is not just terrestrial ecosystems that can become jeopardised by non-native species, freshwater habitats are also extremely vulnerable. The ICAIS (International conference on aquatic invasive species) 2013 report stated that 'the introduction and spread of invasive species in freshwater and marine environments is a worldwide problem that is increasing in frequency'. A recent example is the invasion of the Asian Carp throughout the river systems of Illinois, USA. They were introduced, from China, into water treatment ponds to remove algae in 1970s. The carp escaped and migrated northwards through the Mississippi and Illinois rivers. Although the carp did not cause any extinctions of native species, there was a decline of certain commercial fish such as the big mouth buffalo (Ictiobus cyprinellus). 

Bigmouth buffalo threatened...

Invasive species (in some cases) are considered such a colossal threat because they have the upper hand when resources become scarce.  CSIRO, Australia's national science agency calls invasive species 'one of the greatest threats to biodiversity and to the ecological and economic well being of society and the planet'.

However... not every scientist shares the same assertive view on invasive species. In fact, only a week ago Professor Phil Roberts from the University of York published a paper which throws all opinions up in the air. This is why I love science, its contestable nature. Roberts (2013) discusses how the Anthropocene could raise biological diversity through the introduction of non-native species causing evolutionary hybridisation. He acknowledges that some invasive species damage ecosystems and can eradicate resident species (as I have already explored). However, his discussion remains focused on how people fail to acknowledge that invasive species can also be positive for biodiversity. On average, less than one native species dies out for each introduced species that becomes established. Roberts (2013) neglects cases of invasive species disruption and instead highlights that, despite the fact that we are losing irreplaceable populations, in some (some being the key word here) regions biodiversity is actually increasing.

I will leave you with Roberts (2013) departing words: 

'we have to rethink our "irrational" dislike of invading species'.

I, on the other hand, do not believe that the negative reputation of invasive species is 'irrational', due to the destruction they can and have previously caused. However, it is vital to understand both arguments in order to judge whether there is still hope for biodiversity, in particular at a regional level, despite the doom and gloom of inevitable global species decline.

Anthropocene 0-0 Biodiversity 

What do you think is in the lead? Suggestions welcome!