The world’s oceans are undergoing significant changes – seen in indicators such as temperature and salinity. Isabelle Ansorge and Mike Roberts explain how South Africa is involved in investigations of these changes.

The meridional overturning circulation (MOC) is a system of surface and deep ocean currents that extends across the globe. It is the main way that warm and salty surface waters from the tropics are transported to the poles. In the polar region, the water cools and sinks to great depths. The water then flows southwards as a deep (>2 000 m) ocean current in a process that is called ‘overturning’. In this way, water is returned to lower latitudes. The MOC provides a mechanism for large-scale ocean circulation of heat, freshwater and carbon between ocean basins. This circulation also connects the surface ocean and atmosphere with the huge reservoir of the deep sea.

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A diagram showing the overturning circulation of the global ocean. Throughout the Atlantic Ocean, the circulation carries warm waters (red arrows) northward near the surface and cold deep waters (blue arrows) southward.

The physical structure of this circulation belt and its efficiency in regulating climate is influenced significantly by the way that water masses are exchanged between ocean basins. A few climate models have predicted that increased levels of greenhouse gases may interfere with the MOC process by disrupting or slowing down the circulation. Warming will cause increased glacier melt, increasing the amount of cold, fresh water moving into the Atlantic Ocean. Some scientists predict that the increase in fresh water may be enough to change the composition and flow of ocean water on time scales from decades to centuries.

We know that the MOC provides a vehicle connecting surface and deep ocean currents around the world’s oceans but little is known of the response and degree in which heat is being taken up by the deep oceans. Because of this lack of knowledge the scientific community is slowly realising that we need deep ocean measurements and we need to develop full basin-wide arrays to take these measurements. This is crucial if we want to reduce the uncertainties in model projections of global warming.

Essentially this means that, in order to track the evolving ocean inventory of heat, freshwater and carbon, measurements need to be taken below 2 000 m. Argo floats, gliders and satellite remote sensing have revolutionised our ability to measure the upper layers of the ocean, but the deep ocean is currently beyond their reach. It is becoming more and more obvious that there is a close link between the deep ocean and the climate, so observations need to be taken to areas as deep as the ocean floor. The problem is that the ocean floors are deep and conditions this deep are hostile – particularly in the Southern Ocean.

At the moment there is only one system monitoring the MOC in the North Atlantic Ocean: the RAPID/MOCHA array located at 26.5˚N. Because the MOC covers the world’s oceans it is obvious that changes happening between the South and North Atlantic sectors must be considered.

The importance of the Southern Ocean

The Southern Ocean takes in the southern sectors of the Indian, Atlantic and Pacific basins and provides a link between the upper and lower layers of the global ocean circulation.

Because of this link, the overturning circulation within the Southern Ocean strongly influences climate patterns and the cycling of carbon and nutrients. As a consequence, any changes in the Southern Ocean will affect the rest of the world’s oceans. The observations that have been made so far suggest the Southern Ocean is warming more rapidly than the global ocean average – salinity changes driven by shifts in precipitation and ice melt have been observed and the uptake of carbon has decreased. In response to these changes, Southern Ocean ecosystems are being forced to adapt or are becoming less diverse. There may also be fewer different Southern Ocean ecosystems overall. Unfortunately, the lack of historical observations means that it will take time to understand this region. The scientific oceanographic community really needs an MOC monitoring array across the entire South Atlantic – extending south of Africa because, in spite of the South Atlantic’s climatic importance, there is no observational system in place to monitor the inter-ocean exchanges. Although individual efforts to measure the circulation across natural chokepoints such as the Drake Passage and south of Africa exist, none of these efforts have previously been coordinated, nor have these systems been designed for long-term monitoring. This is where the South Atlantic MOC (SAMOC) comes in. SAMOC-SA has been developed and funded by the National Research Foundation, the Department of Science and Technology and the South African National Antarctic Programme.

How does South Africa fit into SAMOC?

SAMOC is an integrated international observational oceanographic programme extending from south of Africa across the entire South Atlantic (Figure 3). The large meridional gap between the African and Antarctic continents provides a significant crossroad for water mass exchange between the subtropical Indian and Atlantic oceans. Most of the Indian to Atlantic Ocean transfer takes place near the Agulhas Current Retroflection through the generation of large warm rings – known as the Agulhas Leakage. Observations have reported that a highly energetic field of anticyclonic and cyclonic eddies in the Cape Basin interact extensively with each other, resulting in the vigorous stirring of water mass properties and the transport of substantial anomalies of heat from the Indian into the Atlantic Ocean. Recent studies suggest that the Agulhas leakage is critical – through the shedding of Agulhas rings this gateway is one of the major sources of salinity increase in the South Atlantic. Sediment records dating back 15 000 years prove that this leakage correlates to the strength of the North Atlantic MOC. In order to understand the nature of global climate change, the physical understanding and long-term monitoring of the inflow of Indian waters into the Atlantic Ocean is unavoidable. The aim of SAMOC is to improve and deepen this knowledge.

Career opportunities

The state of observations and modelling south of Africa is not as developed as it is in other regions of the world’s oceans. This is largely due to limited ship availability, the lack of available technical support and the lack of sufficient funds to establish a mooring array. As a result South Africa’s role in the international framework of SAMOC has been limited to studies that take place during annual relief voyages into the Southern Ocean. SAMOC-South Africa (SAMOC-SA) provides the necessary tool to pull these surveys into a single entity.

This programme provides future opportunities for all young, early career and established researchers working in the South Atlantic and Southern Ocean to interact and strengthen international and national networks through a set of joint cruise plans. It will provide young students with a variety of bursaries as well as many cruise opportunities on the new SA Agulhas II and will form a crucial role in developing skills, knowledge and expertise of the area – a critical component if South Africa is to retain top-class marine scientists.

The new SA Agulhas II: The ship was commissioned by the Department of Environmental Affairs (DEA) and built in Rauma, Finland by STX. Launched in April 2012, she is currently the most state-of-the-art polar research vessel in the world.  The Agulhas II will form the backbone of the SAMOC-SA programme providing the SAMOC-SA science team of UCT Oceanography and DEA Oceans and Coast scientists and students with a platform to deploy and service the many moorings and measurements along the transect shown in Figure 3.

The planning of a long term observational platform across the entire South Atlantic (Figure 3) takes time but is currently being coordinated between Brazilian, American, French and South African institutes. The new SA Agulhas II (Figure 4) provides the ideal platform to deploy and service the many moorings and undertake ship-based measurements (temperature, salinity, pH, CO₂ etc) along the dedicated transects shown in Figure 3. The SAMOC-SA science team, made up of UCT-Oceanography and DEA-Oceans and Coasts researchers and students, is presently planning Phase 1 of the mooring deployments across the eastern sector of the South Atlantic in mid-October 2013. The recent establishment and endorsement of SAMOC-SA as well as the availability of the SA Agulhas II should mean that these objectives can finally be achieved, so finally placing South Africa in a more pivotal role within the international arena.

The Agulhas current

The Agulhas current flows down the east coast of Africa from 27°S to 40°S. It is a narrow current, fast flowing and strong. The current forms the western boundary of the southwest Indian Ocean.

Mean sea surface temperature map of the Agulhas Current for 2009. Note the separation of the current from the African coast as a warm tongue of water south of Cape Agulhas, as it turns back on itself into the Indian Ocean forming the Agulhas Return Current.

Agulhas current retroflection

The Agulhas current retroflects – turns back on itself – in what is called the Agulhas retroflection. The water from the retroflection becomes the Agulhas return current, which then rejoins the Indian Ocean gyre. A gyre is any large system of rotating ocean currents – particularly those that are involved in large wind movements. The remaining water is transported into the South Atlantic gyre in the Agulhas leakage – through surface water filaments and Agulhas eddies.

Agulhas leakage

A large amount of Indian Ocean water is leaked directly into the South Atlantic. Most of this is warm, salty water – the rest is cold, low salinity South Atlantic water. The Indian Ocean water is significantly warmer and saltier than South Atlantic water, which means that the Agulhas leakage is a significant source of heat and salt for the South Atlantic gyre. The heat exchange probably contributes to the high rate of evaporation in the South Atlantic, which is a key mechanism in the MOC.

Eddies

Eddies are released into the South Atlantic gyre when the Agulhas turns back on itself. Eddies are formed when swirling fluid reverses either in an anticyclonic or cyclonicdirection when the fluid flows past an object. Eddies are common in the ocean and can range in diameter from centimetres to hundreds of kilometres.

The Agulhas rings

In the Agulhas current the eddies form the Agulhas rings, which are warm cores of water that are less biologically productive than the cold water that these rings move into. This means that they carry water with a low concentration of chlorophyll into the South Atlantic –chlorophyll is the pigment that allows photosynthesis. So, the water carried by these rings carries fewer phytoplankton, often smaller in size.

Further reading

Lumpkin R. and Speer K.  Global ocean meridional overturning. J. Phys. Oceanogr. 2007; 37:2550–2562.

Dr Isabelle Ansorge is a senior lecturer in the Oceanography Department at the University of Cape Town. She is an observational oceanographer and spends many weeks at sea in the Southern Ocean. Her research interests are in the Subantarctic Belt and in particular the impact changes in ocean circulation have on the ecosystem of the Prince Edward Islands.

Dr Mike Roberts is an observational oceanographer and is employed at the Department of Environmental Affairs – Oceans and Coasts Division. Mike is one of South Africa’s leading experts in deep-sea oceanographic mooring deployments and has been involved in technical training with the Cape Peninsula Techikon (CPUT) since the early 1990s.

Why do we need a global ocean observing system? by Thomas Mtsonti and Isabelle Ansorge

In the past three decades, discussions of global warming have been restricted mainly to academic debates. Now, however, the same topics provide fuel for public debate and mounting pressure for increasing government action as substantial indicators suggest that climate is undergoing significant variability and change. The flurry of new studies into the climate system have worrying conclusions. However, although the changes seen may be a response of the oceans to global warming, they could just as easily be a natural mode of oceanic variability.

Recent reports have confirmed that sea level is rising at an accelerating rate of 3 mm/year, while August 2012 has seen the Arctic sea ice cover shrink to its lowest level ever. Extreme weather events such as droughts in Africa, intense hurricanes off Florida, unprecedented warm spells in the European winter, dust storms in the Sahara or raging bush fires in Australia are now seen regularly. In the past 10 years we have seen eight of the warmest years recorded since 1860. An understanding of the changes in both the atmosphere and ocean are crucial in order to guide international action and policy. However, a lack of sustained earth observations has hindered the development and validation of the climate models that we need to accurately forecast these changes. In 1998 a plan was put forward to develop a global array of profiling floats throughout the ice-free areas of the deep ocean. This array would, for the first time, provide a systematic robotic monitoring system of the global oceans. That initiative was ARGO.

Getting an Argo float into the water – quick and easy!. SAEON

Where does the name ARGO come from?

The ARGO float programme was designed to operate on the same 10 day cycle as altimetry satellites Poseidon and Jason-1. These satellites are designed to monitor global ocean circulation, but they only measure what happens at the surface of the oceans. ARGO collects data in the upper 2 000 m of the ocean. ARGO is named after the ship in which Jason and the Argonauts set sail in search of the golden fleece, in ancient Greek mythology.

The ARGO Programme”]

There are 3 623 floats currently in operation in the world’s oceans

How does ARGO work?

ARGo is a multi-national network of 3 000 profiling floats. ARGO floats are approximately 1.1 m tall and weigh around 40 kg. The casing is made of aluminum tubing and is strong enough to withstand pressures exceeding 2 000 m. The sensors are able to measure temperature, salinity and pressure. An antennae transmits data from the surface via satellite to over 60 ground stations and from there, the data goes through a series of quality checks before becoming freely available to the public.

The nuts and bolts of the ARGO system

When deployed at the surface, each float sinks to a parking depth of 1 000 m where it drifts for approximately nine day. Before surfacing the float sinks to 2 000 m. On day 10 the float rises to the surface collecting temperature and salinity measurements on the way up. At the surface, the float transmits its data and position via the ARGOS satellite system before repeating another 10 day cycle.

ARGO floats operate on a technique based on differential buoyancy in which an air bladder inflates or deflates, allowing the instrument to sink and rise again to the surface every 10 days. ARGO floats are designed to have a lifetime of three to four years or between 150-200 cycles. The observations will be used to make ‘weather maps’ of the ocean, to initialise climate forecast models for the ocean-atmosphere system and to improve our understanding of the ocean itself. With the array now complete over 100 000 profiles are received each year.

Here is an example of all the data points for one year south of Africa

The advantages of the ARGO system

Problems with ice – what happens?

One of the major problems with research south of Africa is the lack of access and so observations in the Southern Ocean, especially in winter. The Southern Ocean is remote, the environment is hostile and a vast extent of seasonally varying sea ice means that implementing a year-round observing system is challenging. As a consequence the Southern Ocean remains to under sampled when compared to other ocean regions. The current ARGO float array is not equipped to work in the ice. Sensors and the antennae are fragile and easily crushed by sea ice. A new design of ‘ice float’ is currently being tested. The ice floats are standard ARGO floats that have undergone substantial modifications to their temperature sensors. These floats are programmed to check for the presence of sea ice above them using a sea ice detection algorithm. If ice is detected, the data that the float has collected is stored for up to six months. An ice float can work out if there is ice above by calculating the mean water temperature between 20 and 50 m. If the mean temperature is below -1.78 ˚C the float assumes that there is ice in the surface layers and sinks back down to its parking depth. The inclusion of this ice detecting algorithm has resulted in the increase in the survival probability of all floats deployed in the polar regions by over 200%.

Who pays for ARGO?

ARGO is sponsored by two international programmes: the World Climate Research Programme’s CLIVAR which seeks to understand CLImate VARiability and predictability from years to decades. The second sponsor, GODAE (Global Ocean Data Assimilation Experiment) demonstrates the value of real-time operational ocean prediction. The core aim of GODAE is to provide improved ocean observations and forecasts for the scientific and technical community. Each ARGO float costs about $15 000. The array has on average 3 000 floats, but to maintain this number at least 800 floats need to be deployed each year. The total annual cost of ARGO is about $20 million or roughly $25 000 per float-lifetime, which means that each profile costs around $200 or R1 800. The best news is that the data is absolutely free.

Who is involved in ARGO?

Many new countries have joined the original 10 countries who launched floats in 2000. At the latest count 27 countries have deployed or assisted with float deployments.

Teaching ARGO in South Africa

The launch of the first ever African ARGO programme took place in December 2009 when the first South African floats were procured and launched by SAEON (South African Environmental Observation Network) through SANAP. In the past, the SA Agulhas has provided a platform to seed over 200 ARGO floats on behalf of the UK Met and Argo offices in the Southern Ocean – but the acquisition of two Argo floats by SAEON was a first. Scientists from SAEON and the University of Cape Town deployed the two floats while sailing to SANAE (South African National Antarctic base) at 41˚S (within a large ocean eddy) and at 60˚S. Young researchers on board the SA Agulhas were trained in the techniques of deployment. Dr Sebastiaan Swart is one of the South African scientists who uses ARGO data in his research. Dr Swart’s focus is on the Southern Ocean heat and salt fluxes in a remote area about which little is currently known. Hopefully ARGO will fill some of the gaps.

Students learn about ARGO in real time

Teachers and school children from six previously disadvantaged community coastal schools are starting to follow these two ARGO floats as they monitor the track of both floats through the Southern Ocean in a bid to engage and stimulate a new generation of marine scientists. The students are able to download the data from a website and monitor the behaviour of the ocean from their school. Working with the online records as well as interpreting the ocean profile plots and drawing up conclusions from the dataset will undoubtedly boost their skills in science-related activities. Allowing student to access data not only helps them to become comfortable using computers but also provides skill in data analysis and interpretation. The fact that the ARGO Programme is in real time makes this exercise so much more interesting and hands on.

What does the future hold for ARGO?

ARGO is still a young project but its main drive is to reach a permanent global array of 3 000 floats – this will provide over one million ocean profiles over the next 10 years. Although ARGO’s first priority was to complete a basic temperature/salinity array, new sensors such as dissolved oxygen, bio-optic, nutrients, and chlorophyll sensors are necessary to broaden the scientific community base of this programme. ARGO is also limited by the present ARGOS communication system, which restricts the size of data (only 100 depths per profile) per transmission. To ensure reliable data transmission each float must spend several hours at the surface. New communication technologies using iridium coupled with improved GPS navigation promises to remove these restrictions.

Sustainable funding and deplyment opportunities are another challenge.

Where can I find ARGO data?

Argo portal: http://www.argo.net

General information: http://www.argo.ucsd.edu

Coriolis Global Data Centre: http://www.coriolis.eu.org/cdc/argo_rfc.htm

US Global Data Centre: http://www.usgodae.org/argo/argo.html

Dr Isabelle Ansorge is a senior lecturer in the Oceanography Department at the University of Cape Town. She is an observational oceanographer and spends many weeks at sea in the Southern Ocean. Her research interests are in the Subantarctic Belt and in particular the impact changes in ocean circulation have on the ecosystem of the Prince Edward Islands.

Thomas Mtsonti networks with key oceanographic and climatescientists in order to facilitate the integration of marine sciences into school sciences. He has a BSc (Education) from the University of the Western Cape and has worked with people from all sectors of our community. His experience includes teaching high school science and later establishing and managing schools’ outreach programmes.

The Marion Island seal populations have been studied for the last 30 years. Cheryl Tosh and Marthán Bester describe their field research.

Deep in the Southern Ocean, Marion Island is a platform for breeding seals and seabirds such as penguins and albatrosses, with  killer whales patrolling the inshore waters. Because many species to have their young on land there is always life in some form at Marion Island throughout the year. The seal species at Marion Island have their young on land and forage at sea. There are three seal species, the southern elephant seal (Mirounga leonina), the Antarctic fur seal (Arctocephalus gazella) and the Subantarctic fur seal (Arctocephalus tropicalis).

The Prince Edward Islands

The Prince Edward Islands are two small sub-Antarctic islands that are part of South Africa – Prince Edward Island and Marion Island. The island group is about 955 nautical miles (1 769 km) south-east of Port Elizabeth on mainland South Africa. Marion Island (46°54′45″S 37°44′37″E), the larger of the two, is 25.03 km long and 16.65 km wide, with an area of 290 km² and a coastline of some 72 km, most of which is high cliffs. The highest point on Marion Island is Mascarin Peak, reaching 1 242 m above sea level. Boot Rock is about 150 m off the northern coast.

Occurring at the juncture between the African Continental Plate and the Antarctic Plate, Marion Island has been volcanically active for 18 000 years. The first historical eruption was recorded in November 1980 when researchers recorded two new volcanic hills and three lava flows. Researchers observed another small eruption in 2004.

Besides volcanic cones, Marion Island is home to Marion Base, part of the South African National Antarctic Programme. Focusing on biological, environmental, and meteorological research, the base is situated on the island’s northeastern coast.

Studying Marion Island seals

Southern elephant seals have been intensively studied at Marion Island for the last 30 years, under the leadership of Prof. Marthán Bester. Intensive mark-recapture studies followed the comings and goings of elephant seals on the island. As a result of these studies scientists are starting to understand the survival rates of different age and sex classes of the population and the importance of migration and immigration in controlling the population size. All these factors are affected by changes in food resources, which can either be shown by changes in body condition or changes in behaviour.

The behavioural responses of southern elephant seals are studied using state-of-the-art satellite relay data loggers that are attached to the animals. The devices are linked with satellites, and send data about the position of the animal, the water temperature and salinity, and the diving behaviour of the animal, which provides scientists with valuable information about the habitats that these seals are using and how their behaviour changes over time.

Southern elephant seals

Southern elephant seal behaviour shows an enormous amount of individual variation. Some individuals concentrate on feeding in highly productive and stable areas where different marine currents meet – called marine frontal structures. Others feed in short-lasting mesoscale eddies – the unstable areas of the ocean currents that surround the island. Some individuals concentrate on foraging in areas of the ocean that have a particular temperature or current or are at a specific depth. The way that this population spreads its feeding efforts in different parts of the same environment may well be the key to its long term success. Because different individuals can use a variety of habitats they may not compete directly with each other for the same resources. This variation in foraging behaviour will also help the population to withstand changes in their environment.

Recently, researchers at Marion Island have also started to measure changes in body condition of these seals using novel photogrammetrical methods. Dr Nico de Bruyn has developed a protocol using photographs taken with calibrated cameras to build a three dimensional model that shows the volume of elephant seals. Elephant seals are loyal to their birth and breeding sites, so the same animals can be photographed repeatedly in order to build up a time series of three-dimensional models, which may eventually be used to describe body mass changes in response to environmental conditions and behaviour. Researchers have already established that the larger southern elephant seal cows are less likely to breed every year at Marion Island, but in spite of this these cows probably produce more pups than smaller cows over a breeding lifetime.

Fur seals

While the southern elephant seals represent the heavyweights of Marion Island, the fur seal species, the Antarctic and Subantarctic fur seals, represent strength in numbers. Fur seal populations at Marion Island have exploded in the last couple of years, contrary to predictions about climate change affecting food resources negatively. These agile swimmers are often seen torpedoing along the Marion Island coastline until they haul out

at their beach of choice.

Large colonies of seals form during the breeding season, when males aggressively protect small harems of four or five females. Some beaches are densely packed with harems and males are not able to cross another male’s territory once it is established. Any male crossing a territory is seen as a challenger and will be viciously attacked. Such attacks can be fatal. The high drama of the breeding season abates as soon as most of the females have pupped or been mated. After the harems break up the females that have suckled their pups for a few days will leave to forage. The little pups then have a a long wait until their mothers return, during which time they have to fend for themselves. The length of these foraging trips can be an indication of the mother’s foraging success – those that return earlier have found the food they need faster than those who are away for longer. Researchers at Marion Island regularly weigh fur seal pups throughout their suckling period. This growth monitoring, combined with oceanographic indicators, may shed some light into why these animals are so successful at Marion Island.

Researchers are able to monitor where these animals are foraging using satellite relay data technology. We can find out what they have beeing eating by analysing fish ear bones (called otoliths), squid (cephalopod) beaks and other remains sampled from droppings (scats) collected on the beaches. The otoliths and cephalopod beaks are specific to different species.

Orcas – mammalian predators in the sea

While the seals of Marion Island rely on food from the sea, they form an important link in the food chain for yet another large mammalian predator being studied at Marion Island.

Killer whales often come close to the Marion Island coastline and are readily seen by researchers in the field. They circle the island hunting seals and penguins. Nico de Bruyn

Marion Island’s killer whale (Orcinus orca) population feeds on a wide range of prey species that haul out on the island to have their young. The killer whales have been seen hunting penguins, fur seals and even elephant seals. These versatile predators are capable of adapting their hunting strategies to the available prey. They may ambush penguins by hiding out of sight while a lone killer whale chases the penguins in the direction of the waiting pod. They also lay siege to seal colony beaches, waiting for elephant and fur seals to leave their beaches. These abundant food resources mean that killer whales are always around Marion Island in the summer. Individuals and family groups have been identified over years of research and intensive observations. It appears that the same individuals are present at Marion Island for large parts of the year. During winter the whales leave the island, and satellite telemetry is used to find out where these animals are going during the winter months.

Field research

Every year, as part of the annual overwintering team, a team of biologists braves gale force winds, ice pellet storms and torrential rains to monitor, weigh and observe southern elephant seals, fur seals and killer whales.

A typical day for a seal researcher includes waking up as the sun rises, looking out of the window to check the weather, having breakfast, looking out of the window to check the weather, packing your backpack and pulling on your gumboots and looking out of the window to check the weather. Eventually it is time to step out of the door – whatever the weather. On most days, researchers will walk along the Marion Island coastline checking every beach for southern elephant seals. Every elephant seal is then checked for a flipper tag and the colour and number is noted in order to identify individuals. This often involves traversing rocky beaches in bad weather, using rope ladders to climb down cliffs and wading through penguin colonies splattered with dropping in order to get to elephant seals.

Once a month, seal researchers brave needle sharp fur seal teeth while weighing 100 fur seal pups. The first weighing just after the pups are born is easy, with most pups weighing in at around 3 kg. Towards the end of the suckling period, the healthy, agile survivors weigh in at between 10 – 15kg. As if sprinting over treacherous terrain in gumboots to catch pups is not enough, researchers will have weighed over a ton of fur seal pups by the end of the day. Some researchers have also received nips from concerned fur seal mothers in recognition of their efforts on the beaches.

A southern elephant seal cow and newborn pup. Researchers maintain a respectful distance while watching the cow bond with her pup. An Antarctic skua (Stercorarius antarcticus) looks on – ready to pounce if the opportunity arises.

Southern elephant seals and fur seals have satellite transmitters fitted. But researchers have to wait for good weather before they can do this – not something that happens very often.

Satellite transmitters can only be deployed when the seals’ skins are dry. Southern elephant seals are immobilised using specialised drugs, which means that all researchers have to do a wildlife immobilisation course before going to the island. The drugs are given using a spinal needle, a length of drip tubing and a syringe. Only when the seal is immobilised does the deployment team approach the animal with the device and the epoxy resin. They then stick the device onto the seal while monitoring its breathing. They wait until the seal has recovered fully and is able to move independently.

Catching a fur seal in a hoop net requires stealth and finesse. The scientist spots a fur seal mother from a distance while she is basking in the sun, goes into stealth mode, holding the hoop net at the ready for last 10 m of the ambush. The fur seal mother looks up, sees the scientist and runs away… attempt aborted! All the fur seals on the beach are now alerted to the intruder and some flee to the sea. The scientist now has to try at another beach. Eventually, after perhaps three or four attempts, the scientist manages to catch a fur seal mother unawares, deploys a transmitter, weighs her and releases her – and there are still five more transmitters that have to be deployed…

The Marine Mammal Research Programme at Marion Island would not be in existence without the dedication and determination of researchers prepared to leave their families and homes in order to conduct research for 13 months on a remote island in the middle of the Southern Ocean.  These dedicated scientists are responsible for collecting data that provide valuable insights in the biology of seals and killer whales in the Southern Ocean. Seal research on Marion Island is not for the faint hearted, but every scientist that has had the privilege to be involved with the programme will tell you that the rewards are endless – a real life-changing experience. A beautiful sunset, an elephant seal giving birth, a fur seal porpoising  through the water or watching killer whales resting for two hours almost within touching distance make it all worthwhile.

Cheryl Tosh currently studies the foraging behaviour of Marion Island’s southern elephant seals. She spent 13 months on Marion Island as a seal researcher and is a post-doctoral fellow at the University of Pretoria. Prof. Marthán Bester heads up the Marion Island Marine Mammal Programme. His research is focused on the biology of marine mammals at Marion and Gough Islands.

Even the remote Antarctic continent and its sub-Antarctic islands and seas are troubled by invasive alien species. By Anne M Treasure

The introduction of invasive alien species has been recognised as a major threat to biodiversity and ecosystems and the resulting effects have been recorded around the world. In fact the Global Invasive Species Programme (http://www.gisp.org) has identified that the spread of invasive alien species is one of the most significant ecological and economic threats to the planet. Humans have served as both accidental and deliberate dispersal agents of invasive alien species and the frequency and extent of introductions worldwide is alarming.

What are invasive alien species and why are they a problem?

Alien species (also called introduced, exotic, non-native, or non-indigenous species) are those plants, animals or any other types of organism, that are found in areas where they did not occur naturally in the past. These species were introduced through the accidental or deliberate actions of humans. An alien species that manages to maintain a large reproducing population with the potential to spread over large areas is known as an invasive species. Invasive species can cause a number of problems costing millions of rands of damage every year by, for example, being agricultural pests or vectors of disease. Invasive species that spread can outcompete and exclude indigenous species that occur in the area naturally. In this way, natural species interactions are disrupted, changing ecosystems and the services they deliver. Invasive species can also lead to the extinction of indigenous species.

Invasive species are found in every taxonomic group, from viruses, fungi and plants to invertebrates, birds and mammals. These species have had substantial impacts in virtually every region and habitat on earth. Despite its remoteness, Antarctica is no exception.

Definitions

Endemic species: A species that is only found in a particular geographic location and nowhere else in the world.

Indigenous/native species: A species that occurs naturally in an area, without human intervention. Not all indigenous species are endemic species, as an indigenous species can naturally occur in more than one area.

Alien species: A species of plant, animal or any other type of organism found in an area where it did not naturally occur in the past. Its presence in this area is due to deliberate or unintentional human involvement.

Naturalised or established species: An alien species that has maintained a reproductive population for at least 10 years without direct intervention by people.

Invasive species: An alien species that manages to maintain a large reproducing population with the potential to spread over large areas.

Invasions in the Antarctic

The Antarctic region includes the Antarctic Continent and Peninsula, sub-Antarctic islands and the Southern Ocean.

Alien microbes, fungi, plants and animals occur on most sub-Antarctic islands and some parts of the Antarctic continent and ocean. The consequences of invasive species in Antarctica are widely reported and impacts on indigenous species and communities have been recorded. There has therefore been much interest in the region, particularly as it is of considerable conservation importance due to the large number of indigenous and endemic species found there. In the past, rats and mice were inadvertently introduced from visiting ships to many sub-Antarctic islands.

A tagged invasive house mouse (Mus musculus) on Marion Island. Tags are used for mark and recapture studies, which allow scientists to collect data on the population sizes of these small invasive mammals. Mice are having significant impacts on the ecosystems of many sub-Antarctic islands. Anne Treasure

Islands have also seen the intentional introduction of species such as rabbits (on Kerguelen and Macquarie) and reindeer (on South Georgia and Kerguelen) for food, or cats on Marion and Macquarie islands. Once feral, these animals started causing widespread environmental damage. For example, introduced cats on Marion and Macquarie islands substantially reduced seabird populations before they were finally eradicated by the early 1990s on Marion and by 2000 on Macquarie. Rabbits and reindeer cause severe damage to native vegetation. Invasive mice have been introduced to numerous islands such as Marion, Macquarie, South Georgia, Crozet and Kerguelen where they are having severe impacts on indigenous invertebrates and plants. Mice and rats also pose a serious threat to seabirds on which they are known to prey. The Kerguelen archipelago is the island group with the highest number of invasive mammals and is suffering large consequences due to seven invasive species now present on the islands: mice, rats, rabbits, sheep, reindeer, mouflon and cats.

Invasive plants and invertebrates (mostly introduced unintentionally through, for example, animal fodder, cargo (including food supplies) or attached to clothing, are widespread on most islands and have also been found on the Antarctic Peninsula. These introductions have had considerable impacts, which include direct reductions in population sizes of indigenous species, as well as changes in food webs and the functioning of ecosystems. The introduction of fungi, microorganisms and diseases have also been linked to human activities.

The invasive springtail Pogonognathellus flavescens coated with fluorescent powder, on Marion Island. Using a black-light-blue bulb that picks up the fluorescence at night, it is possible for scientists to track the movements of such invertebrates. Such studies provide vital information about the patterns and speed at which invasive species spread. Anne Treasure

These threats are set to continue as the Antarctic is facing an increase in the rate of introduction of invasive species. This is mostly because the routes for colonisation have increased substantially due to increased human traffic to Antarctica. Tourist numbers have increased three-fold from 1998/1999 (10 013) to 2010/2011 (33 824) (available on http://iaato.org). Furthermore, government operators now employ around 5 000 scientists and support staff, who visit the region for short or long time periods, and there are over 65 year-round and summer-only research stations in Antarctica. Each of these stations has to be resupplied at least once a year with personnel, food, cargo and building materials. The number of ships as well as aircraft entering the region has increased, meaning that there are many more opportunities for alien species to be introduced. In addition, many tourist and research vessels go from place to place covering a number of different Antarctic and sub-Antarctic locations. Therefore, species that are already pre-adapted to cold conditions in their native region may be transported to other regions within Antarctica where they do not occur naturally.

Although many countries now have stricter controls to prevent introductions than were in place in the past, terrestrial alien species are still brought into Antarctica in cargo and attached to clothing, and marine species are introduced by hull fouling, the intake and subsequent discharge of ballast water, scientific equipment or they can be transported on floating man-made debris. Marine introductions are of a particular concern as most visitors and cargo are transported to the Antarctic in ships. However, much less is known about marine invasions than about terrestrial invasions. This is in part due to poor knowledge of the diversity of many near-shore environments in Antarctica, which makes it difficult to identify whether invasive species have been introduced.

The first alien marine species to be recorded in Antarctic seas was the North Atlantic spider crab (Hyas araneus). Both a male and a female of this shelf species, native to the North Atlantic and Arctic Oceans, was found on the Antarctic Peninsula in 2004. It is suspected that this species entered Antarctic waters either on ships’ sea-chests or through ballast water. The invasive green alga Enteromorpha intestinalis is also thought to have been introduced via the hulls of visiting ships and now grows in dense mats on intertidal rocks on the South Shetland Islands. These pathways for marine invasions are a significant threat. A study on the highly invasive Mediterranean mussel (Mytilus galloprovincialis) showed this species to predominate in the sea chests of the South African polar vessel the S.A. Agulhas and that at least some of these individuals survived multiple voyages to the Antarctic region.

The survival of this species in Antarctic conditions demonstrated that the mussels are capable of surviving polar conditions, at least in the short-term. This study also highlighted the limited effectiveness of antifouling technology employed by such vessels. Another potential source of marine introductions is transport used on re-supply expeditions for ship to shore transfers. The presence of large numbers of organisms found on the bottom of a barge taken from Hobart, Australia, to Macquarie Island for this purpose (including algae, barnacles, numerous crustaceans, starfish, mussels, and crabs) highlighted this risk.

Attempts to introduce salmonid fish have been made at a number of islands, including the Falklands, Kerguelen, Possession, Crozet, South Georgia and Marion. These fish only flourished on Kerguelen, which has relatively large rivers. Once introduced to a few rivers, the fish were able to expand their territory to neighbouring rivers by short sea migrations.

Invasive eradication: Dr Jennifer Lee

What is your current job and what does it entail?

I work as the Environment Officer for the Government of South Georgia and the South Sandwich Islands. I am responsible for all matters related to managing the terrestrial environment, including biosecurity and habitat restoration. Lots of my work is about policy and ensuring that the government meets its obligations to international agreements such as the Agreement on the Conservation of Albatross and Petrels. About half of my time is spent in the office planning and writing policy documents and the other half is spent in the field overseeing various environmental management projects.

Dr Jeniffer Lee

What invasive problems do you face on the islands and what impacts are these invasions having?

Although there are now strict measures in place to prevent the introduction of alien species, early whaling and sealing expeditions introduced a number of non-indigenous species to South Georgia. Some species such as rats and dandelions were introduced accidentally, whereas others such as reindeer were deliberately introduced as a source of food. At the time, nobody knew what impact these species would have, but in the absence of natural predators or disease populations have grown rapidly and there are severe impacts on the island’s native flora and fauna. In particular rats and reindeer both have severe impacts on the islands burrowing bird species. Rats eat chicks and eggs and reindeer graze vegetation above the burrows causing the ground to dry out and the burrows collapse. Reindeer also facilitate the spread of non-native plant species like the annual blue grass, which thrives in the disturbed ground.

How are you controlling these?

Currently there are programmes in place to eradicate both rats and reindeer from the island. Rats will be eradicated by dropping poison bait from helicopters. This is the largest rat eradication programme that has ever been attempted. Reindeer will be controlled by herding them from outlying areas to a central point where they will be killed under veterinary supervision. Controlling invasive species is very costly. The rat and reindeer eradication projects will cost millions of pounds. There are also environmental impacts of eradication attempts. When poison bait is dropped to kill the rats, they will probably also be eaten by some of the native birds such as pintails and sheathbills. When these birds and the rats die, larger birds will eat the carcasses causing the poison to build up in the food chain. However, even though it is expected that some birds will die, it is likely that populations will recover rapidly once the rats have been removed.

What is your background and what previous work have you done on invasions?

I did my PhD and post-doctoral research at the Centre for Invasion Biology at Stellenbosch University. I worked closely with the South African National Antarctic Programme to look at how invasive species moved into and around the Antarctic region. I was lucky enough to be able to work on both marine and terrestrial systems and looking at what sort of alien species were being transported inside ships going to the Antarctic and what was being carried underneath them on their hulls.

What skills and aptitudes do you need to do a job like this?

To work as an environment officer you need to be able to think on your feet and face up to a challenge. The daily workload is incredibly varied and can involve anything from issuing permits so scientists can collect samples for their research to planning how to herd reindeer across a rugged mountain pass. One of the big attractions of the job is being able to spend time on South Georgia. However, when in the field the hours are long and the accommodation is basic (usually a tent!). It is important to be able to work independently, be physically fit and able to look after yourself and those around you in a remote environment.

Implications of climate change

The low temperatures in Antarctica represent a significant challenge to survival for alien species. However, the Antarctic is facing rapid climate change, which is predicted to facilitate the introduction of invasive species. Interactions between climate change and invasive species are poorly understood, but evidence for such interaction is accumulating. For example, warming conditions can facilitate colonisation success and give invasive species a physiological advantage over indigenous species. Warming conditions can also facilitate easier dispersal of invasive species. This is already well documented on sub-Antarctic islands for invasive plants and invertebrates. Warming waters would also favour increased transport, establishment and spread of marine alien species. Increasing temperatures can also enable species to expand their ranges into new areas faster than would occur naturally, which can have serious consequences for native species that have not evolved defences against such intrusions. For example, warming of the Western Antarctic Peninsula shelf waters appears to be facilitating the movement of the cold-intolerant king crab (Neolithodes yaldwyni) into this area. This crushing predator is having devastating ecological effects on the shelf, where they voraciously prey on echinoderms (the group of animals that includes the starfish and sea urchins). Antarctic marine invertebrates are inherently weakly calcified, making them particularly susceptible to the crabs. The crabs are also modifying the physical environment and altering other animals’ habitat by disturbing sediment on the seafloor when they dig for worms and other creatures. Intrusion of sub-Antarctic waters into Antarctica has also resulted in alien species, most probably of South American origin being found off King George Island.

Control and the future

Eradicating an alien marine or terrestrial species once it has become invasive is difficult and costly, and most times impossible. In fact, there are no reports of successful removal of a marine invasive species from the sea once they have invaded. Therefore, the best way to combat the problem is to prevent alien species from reaching Antarctica in the first place. Awareness of the risks that visitors may pose to ecosystems in Antarctica and the sub-Antarctic through the introduction of alien species has increased in recent years. Because of this, some national and tourism operators have implemented quarantine procedures such as boot washing and educational programmes. Various types of inspection, washing and extraction procedures can be done to minimise terrestrial introductions. Cargo should be cleaned properly and fumigated if necessary. Prevention should focus on pre-departure measures first, but biosecurity officers with biological backgrounds should also accompany all voyages to the region to undertake supervision of clothing and equipment cleaning en route. Good examples of further policies are ones that South Africa has in place for Marion and Prince Edward Islands such as banning the importation of fresh produce (which could contain invasive insect pests or fungi) and chicken on the bone (which could introduce bird diseases), and irradiating fresh chicken eggs (also to prevent bird diseases).

Modern shipping can quickly move species thousands of kilometres against natural barriers to migration such as currents. Measures can be taken to prevent marine invasions such as painting the hulls of ships with anti-fouling paints to prevent marine organisms from attaching to the boats. Guidelines are also in place for the management of ballast water in Antarctica (see http://www.ats.aq/documents/recatt/Att345_e.pdf). Awareness of the potential risks are crucial and simple changes to operating procedures may reduce the chance of introductions in the future. For example, changing the length of time that ships stay in port before visiting Antarctica thereby reducing the opportunity for invasive species to establish on hulls.

If limiting or reducing the number of visitors to the region is not possible, then education to increase awareness for all involved in activities in the region is key, including managers of national programmes, visitors (tourists and scientists), crew of boats (tourist, scientific and fishing), tour operators and cargo facility staff. Various resources are available for this, including documentation (see for example pamphlets on: http://iaato.org/dont-pack-a-pest, http://iaato.org/decontamination-guidelines, http://www.asoc.org/storage/documents/tourism/ASOC_Know_Before_You_Go_tourist_pamphlet_2009_editionv2.pdf) and videos (for example Instructional video on cleaning (Aliens in Antarctica Project, 2010: http://academic.sun.ac.za/cib/video/Aliens_cleaning_video%202010.wmv).

If prevention has not been possible, then early detection and quick response is vital. Having good baseline data on indigenous species is important and regular monitoring of sites (particularly high risk sites such as around research stations or tourist visitation sites) is essential. If an invasive species is detected, an eradication programme should be implemented as soon as possible to prevent the species from spreading and to make the eradication more cost effective. The quicker the response, the more effective the eradication will be. Follow up surveys should be conducted to ensure that the eradication was successful. If eradication is not possible, regulation and control of the invasive populations should be explored.

Marion Island’s pristine and breathtaking landscape Anne Treasure

Much research is being conducted on invasive species in Antarctica and the impacts they have on indigenous species and ecosystems (see for example www.sun.ac.za/cib). Findings from this research inform policy and international collaborative programmes to combat the problems. An inter-disciplinary committee called the Scientific Committee for Antarctic Research (SCAR: www.scar.org) is charged with initiating, developing and coordinating high quality international scientific research in the region. SCAR also provides scientific advice to Antarctic Treaty Consultative Meetings and makes recommendations that influence policy and international agreements, which provide protection for the ecology and environment of the Antarctic. Working in this field is very rewarding as one can make a real difference to the conservation of this unique and beautiful part of the world.

Dr Anne Treasure is a postdoctoral research fellow in the Oceanography Department at the University of Cape Town. Her research focuses on ecosystem responses to climate

change-driven shifts of the sub-Antarctic front in the vicinity of the Prince Edward Islands. She completed her PhD on the impacts of invasive species and climate

change on Marion and Prince Edward Islands.