Antarctica may not be as isolated as we thought, and that’s a worry

Ceridwen Fraser, Australian National University

For a long time, we have thought of Antarctica as isolated from the rest of the world. The continent is entirely surrounded by the Southern Ocean, which heaves with giant waves whipped up by intense winds, and is home to the world’s strongest ocean current, the eastward-flowing Antarctic circumpolar current (ACC).

The Southern Ocean is associated with several circumpolar oceanic fronts (see image below), where sharp transitions in ocean temperature and salinity occur.

Approximate positions of the Antarctic polar front and the subtropical convergence, which are the northern bounds of Antarctic and sub-Antarctic water, respectively.
Ceridwen Fraser, Author provided

One of the most significant of these is the Antarctic polar front, a convergence zone where cold Antarctic water sinks under warmer sub-Antarctic water.

Ocean barrier

The polar front was considered as a barrier blocking movement of marine plants and animals into and out of Antarctica.

Many groups of organisms show strong differences on either side of the front, suggesting northern and southern populations have been separated for a long time. We know from genetic work that some species, such as some molluscs and crustaceans, have managed to cross the front in the past, but there is little evidence that biological movement across the front can or does still occur.

Some live adults and larvae of crabs that hadn’t previously been found south of the polar front have recently been detected in Antarctic waters, but there is doubt about whether these are true invaders from the north, or have been around Antarctica for thousands of years.

Species on the move

Globally, many species are either moving up mountains or towards the poles as the Earth warms. This trend has been going on since the end of the last Ice Age, but is accelerating as global warming speeds up due to human influences.

In the Northern Hemisphere, shallow waters and continental land span almost all latitudes from the tropics to the poles (see image, below), making it straightforward for many tropical and temperate species to move north.

Pole-centred globes showing the oceanic isolation of Antarctica compared to the more continental Northern Hemisphere.
Ceridwen Fraser, Author provided

But in the Southern Hemisphere, the Southern Ocean gets in the way of plants and animals trying to head to higher latitudes.

Many species that are already on the southern tips of continents such as South America, Africa and Australia face extinction if they cannot move south as the climate warms.

Antarctica’s unique ecosystems

Antarctic ecosystems are unique; they feature large numbers of species not found anywhere else in the world.

Many Antarctic species are slow growing. Antarctic lichens, for example, take between 100 and 1,000 years to grow one centimetre.

Antarctic species have adapted to extreme conditions where evolving strategies to compete with other species has been less important than evolving ways of dealing with intense cold and desiccation. As a result, most Antarctic species are poor competitors.

New arrivals could cause major ecosystem shifts and sharp declines in native species. Some such impacts have already been seen with invasive species reaching sub-Antarctic islands.

To protect Antarctica’s fragile ecosystems from the impacts of invasive species, efforts are being made to limit the chance of humans (tourists and scientists) moving exotic species into the polar region.

The chance of non-native species finding their own way in has generally been considered too remote to pose a major threat.

Antarctic penguins watch the ocean.
Ceridwen Fraser, Author provided

Crossing the Antarctic Polar Front

Modelling and oceanographic research has started to indicate that the polar front is not the unbroken, continuous barrier was thought to be. Rather, it is a dynamic, shifting series of water jets that can be breached by features such as eddies, which transport pockets of water through the convergence zone.

New evidence published this month from observations of floating kelp at sea indicates that drifting marine species can cross the polar front and enter Antarctic waters from the north.

On each of three separate ship voyages – one in the Atlantic Ocean (2013-2014), and two in the Indian Ocean (2008 and 2014) – many detached pieces of kelp species that grow in the sub-Antarctic were observed floating on both sides of, and across, the polar front.

Southern bull-kelp grows abundantly in the sub-Antarctic but can drift long distances at sea.
Ceridwen Fraser, Author provided

Floating kelps act as the “taxi service” of the sea, forming rafts that can transport diverse species – even entire communities – across hundreds of kilometres of open ocean.

At the moment, the absence of most of these species from Antarctic shores suggests that cold and ice are stopping them from successfully colonising polar environments.

Some groups, at least, seem able to disperse across the polar front and enter Antarctic waters.

Antarctica has some of the fastest-warming regions of the world, and with less ice and warmer waters, many shallow-water marine species from the north could colonise and establish, irrevocably changing the structure of Antarctic marine ecosystems.

Ceridwen Fraser, Lecturer, Australian National University

This article was originally published on The Conversation. Read the original article.

Advertisement

We’re kidding ourselves if we think we can ‘reset’ Earth’s damaged ecosystems

Martin Breed; Andrew Lowe; Nick Gellie, and Peter Mortimer, Chinese Academy of Sciences

Earth is in a land degradation crisis. If we were to take the roughly one-third of the world’s land that has been degraded from its natural state and combine it into a single entity, these “Federated States of Degradia” would have a landmass bigger than Russia and a population of more than 3 billion, largely consisting of the world’s poorest and most marginalised people.

The extent and impact of land degradation have prompted many nations to propose ambitious targets for fixing the situation – restoring the wildlife and ecosystems harmed by processes such as desertification, salinisation and erosion, but also the unavoidable loss of habitat due to urbanisation and agricultural expansion.

In 2011, the Global Partnership on Forest and Landscape Restoration, a worldwide network of governments and action groups, proposed the Bonn Challenge, which aimed to restore 150 million hectares of degraded land by 2020.

This target was extended to 350 million ha by 2030 at the September 2014 UN climate summit in New York. And at last year’s landmark Paris climate talks, African nations committed to a further 100 million ha of restoration by 2030.

These ambitious goals are essential to focus global effort on such significant challenges. But are they focused on the right outcomes?

For restoration projects, measuring success is crucial. Many projects use measures that are too simplistic, such as the number of trees planted or the number of plant stems per hectare. This may not reflect the actual successful functioning of the ecosystem.

Meanwhile, at the other end of the scale are projects that shoot for outcomes such as “improve ecosystem integrity” – meaningless motherhood statements for which success is too complex to quantify.

One response to this problem has been a widespread recommendation that restoration projects should aim to restore ecosystems back to the state they were in before degradation began. But we suggest that this baseline is a nostalgic aspiration, akin to restoring the “Garden of Eden”.

Beautiful, but not particularly realistic.
Wenzel Peter/Wikimedia Commons

An unrealistic approach

Emulating pre-degradation habitats is unrealistic and prohibitively expensive, and does not acknowledge current and future environmental change. While a baseline that prescribes a list of pre-degradation species is a good place to start, it does not take into account the constantly changing nature of ecosystems.

Instead of a “Garden of Eden” baseline, we suggest that restoration projects should concentrate on establishing functional ecosystems that provide useful ecosystem services. This might be done by improving soil stability to counter erosion and desertification, or by planting deep-rooted species to maintain the water table and reduce dry land salinity, or by establishing wild pollinator habitats around pollinator-dependant crops such as apples, almonds and lucerne seed.

Natural ecosystems have always been in flux – albeit more so since humans came to dominate the planet. Species are constantly migrating, evolving and going extinct. Invasive species may be so prevalent and naturalised that they are impossibly costly to remove.

As a result, land allocated for restoration projects is often so altered from its pre-degradation state that it will no longer serve as habitat for the species that once lived there. Many local, native species can be prohibitively difficult to breed and release.

And present-day climate change may necessitate the use of non-local genotypes and even non-local native species to improve restoration outcomes. Newer, forward-thinking approaches may result in the generation of novel gene pools or even novel ecosystems.

Projects should focus on targets that are relevant to their overarching goals. For example, if a restoration project is established to improve pollination services, then the abundance and diversity of insect pollinators could be its metric of success. As we argue in correspondence to the science journal Nature, restoration should focus on helping to create functional, self-sustaining ecosystems that are resilient to climate change and provide measurable benefits to people as well as nature.

An excellent example of a successful, large-scale restoration project with targeted outcomes is Brazil’s ongoing Atlantic Forest Restoration Pact. This has committed to restoring 1 million hectares of Atlantic forest by 2020 and 15 million hectares by 2050.

This project has clear objectives. These include restoring local biodiversity (for conservation and human use, including timber and non-timber forest products); improving water quality for local communities; increasing carbon storage; and even creating seed orchards that can be either sustainably harvested or used to provide more seeds for sowing as part of the restoration.

This project has clear social objectives as well as ecological ones. It has created new jobs and income opportunities. Local communities are contributing to seed collection and propagation, while the project gives landowners incentives to abide by laws against deforestation. For forests, this is the kind of pragmatic approach that will bear the most fruit.

Martin Breed, ARC DECRA Fellow; Andrew Lowe, Professor of Plant Conservation Biology; Nick Gellie, PhD Candidate, and Peter Mortimer, Associate professor, Chinese Academy of Sciences

This article was originally published on The Conversation. Read the original article.