Focus on northern aquaculture industry

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Parliament’s Joint Select Committee on Northern Australia met in Broome and Perth in June as part of its investigation into opportunities to expand the aquaculture industry in Northern Australia.

Aquaculture is the farming of captive-bred stock or naturally occurring juveniles of wild caught stocks and it is Australia’s fastest growing primary industry, accounting for 34 per cent of total gross value of seafood production.

The inquiry follows findings and recommendations in the committee’s Pivot North Report that the Government facilitate the development of the aquaculture industry in Northern Australia by improving the regulatory framework.

The Commonwealth Scientific and Research Organisation identified about 594,000 hectares in Queensland, 528,000 hectares in the Northern Territory, and 516,000 hectares in Western Australia as being suitable for aquaculture.

“This is an area greater than the combined land area of Brisbane, Darwin and Perth and demonstrates there is significant potential for farming sea and freshwater products along coastal regions of Northern Australia,” Committee Chair, the Hon Warren Entsch MP said

The Western Australian Government recently announced the creation of the Kimberley Aquaculture Development Zone.

“This initiative has the potential to boost aquaculture on the north west of Australia, and improve employment opportunities in the Kimberley region,” Mr Entsch said.

Pearl farmers, local shires and the Kimberley Training Institute’s Aquaculture Centre gave evidence at the hearings in Broome while companies and organisations with an interest in the Kimberley Aquaculture Development Zone presented to the committee in Perth.

OEPA Marine Ecosystems Manager and WAMSI Dredging Science Node Leader Ray Masini fronted the committee in Perth representing Environmental Protection Authority Chairman Paul Vogel.

“The Committee was very interested in the work of WAMSI generally, and in particular the Kimberley Node, which will provide important contextual information to support strategic planning in this important part of northern Australia. This was a perfect opportunity to table the Blueprint for Marine Science 2050 focussing on the research needs identified for the aquaculture sector developed through extensive stakeholder consultation,” Dr Masini said.

In response to the meetings, Northern Australia Committee deputy chair Alannah MacTiernan said, “Science needs a full seat at the table in planning for aquaculture in northern Australia.”

“There is enormous potential for further development of an aquaculture industry in the North West, but what is clear is that we need to embrace science and research to ensure we get the optimum result,” the deputy chair said.

Hearing programs are available at www.aph.gov.au/jscna

Sponges choose enigma over charisma

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While sea sponges may not be as charismatic as corals, an industry funded WAMSI project is finding their strength may lie in their resilience to change.

One of the most important roles of the sponge is providing habitat for vertebrate and invertebrate species, but one of the most impressive is its ability to filter huge volumes of water – a one kilogram sponge can filter more than 20,000 litres of sea water every day. It makes them a critical link between what’s happening in the benthic environment (the ecological region at the very bottom of the sea) and what happens in the pelagic zone (mid to surface region).

Because they have a big influence on what’s happening around them, a team of researchers at the Australian Institute for Marine Science (AIMS) led by Dr Nicole Webster is testing their sensitivity to reductions in water quality.

Mari Carmen Pineda monitoring sponges in the AIMS SeaSim lab

“Field surveys of the filter feeding communities in the Pilbara region led by Drs Jane Fromont and Christine Schoenberg really highlighted the amazing diversity and abundance of sponges,” Dr Webster said. “It has confirmed that sponges are the dominant filter feeders.”

“This project is looking at sponges of different species, different morphologies and different nutritional strategies to see how they respond to the various dredging related pressures,” she said.

Little is understood about the effects of dredging pressures on sponges. However, some of the known effects include bleaching or the loss of photosynthetic microbes from low light conditions, clogging of their aquiferous systems from high levels of suspended solids or complete burial or smothering of the sponges due to high rates of sedimentation.

Sponge filtration capability

The sponge’s aquiferous system is made up of channels and small chambers lined with specialised cells (choanocytes) that create currents of water and retain nutritive particles.

It’s quite well known that sponges can reduce their pumping activity in response to high levels of particulates in the sea water, but how long they can maintain that reduction in pumping activity before their energy reserves, which they need for growth and reproduction, become entirely depleted is not yet known.

Dr Mari-Carmen Pineda and PhD student Brian Strethlow are testing the sponges under controlled conditions in the AIMS National Sea Simulator (SeaSim) to define cause/effect relationships to the dredging related pressures of light attenuation, sedimentation (smothering) and elevated suspended sediments (clogging).

Carteriospongia foliascens with  mucus and sediment layer sloughing
Cliona orientalis with brittle star inside its osculum cleaning the sediments

“To determine the sponge stress response we measure a whole suite of health parameters in our experimental animals including: changes to respiration rates, bleaching or loss of symbiotic microbes, changes to sponge pumping activity and cellular necrosis,” Dr Pineda said.

“Overall we are finding that sponges seem largely tolerant of short term dredging-related pressures and that light and suspended sediments on their own do not cause severe stress in the short time (days),” she said. “Sponges also demonstrate an array of different mechanisms for coping with sedimentation, such as the development of new oscula (exhalent pores), sediment sloughing and removal of sediment from the aquiferous canals by infauna

Coscinoderma matthewsi with open osculla through the sediment layer

such as brittle stars. “

“On the other hand, long-term exposure (>2 weeks) to dark conditions and high levels of suspended sediments (>30 mg/L), seems to have an impact on growth rates and symbiotic microbes, although most sponges can recover once conditions return to normal.

“Overall, cup shaped sponge morphologies and phototrophic species (ie those that rely on photosynthetic microbial symbionts for nutrition) are the most sensitive to dredging related impacts, and some of them do not possess the ability to recover,” Dr Pineda said.

The SeaSim experiments will add to data gathered from pre-dredging surveys by divers and towed video. The field surveys are also due to be repeated in July post-dredging off Onslow to determine what changes have occurred and how this can be applied to management of dredging operations in the future.

This research was funded by Woodside, Chevron, BHP and WAMSI partners

 

The WAMSI Dredging Science Node is made possible through $9.5 million invested by Woodside, Chevron and BHP as environmental offsets. A further $9.5 million has been co-invested by the WAMSI Joint Venture partners, adding significantly more value to this initial industry investment. The node is also supported through critical data provided by Chevron, Woodside and Rio Tinto Iron Ore.

Category:

Dredging Science

Exploring innovation to monitor the humpback whale

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As the annual humpback whale migration begins from the Antarctic to the Kimberley coast, one WAMSI project, working to model their spatial distribution, is looking to combine satellite imagery and bathymetric LiDAR (Laser or Light Detection and Ranging) for the first time as an efficient and safe means to monitor these giants of the sea.

The number of humpback whales travelling the coast of Australia from their feeding grounds in the Antarctic to their breeding grounds in the Kimberley has increased from around 300 in 1963 to some 30,000 today since hunting was outlawed.

The challenge now for lead researcher on the WAMSI project Michele Thums, from the Australian Institute of Marine Science, is to map habitats that are important to them when they are on their breeding grounds in the Kimberley which, in turn, could help to manage marine park boundaries and the potential to overlap with human activities such as boating and industry.

“We already understand quite a lot – timing of the migration, spatial extent of the calving area, and general distribution of migrating whales but there has been very little attempt to bring this data together and synthesise it to get a quantitative understanding of their habitat requirements and the specific habitats that breeding humpbacks rely on,” Dr Thums said.

The project is analysing data from some of the extensive aerial and vessel line transect surveys gathered over the last 25 years mostly on behalf of industry. This study is predominantly relying on data released by WAMSI research collaborator Curt Jenner, Inpex and Woodside.

“It’s very expensive to do these surveys,” Dr Thums said. “Collecting data from aerial and boat surveys is especially prohibitive in the Kimberley because it is so remote. So we’re fortunate to get access to this rich source of data collected by industry as part of their legislative requirements to operate.”

In September the project team is going to take an opportunity to head out into the field and test the reliability of monitoring whales using a scanning laser fixed to an aircraft that is capable of generating precise 3-dimensional information about the characteristics on the earth’s surface (bathymetric LiDAR system), in this case whales.

“We’re still developing this project but, if successful, it doesn’t require observers on the flight, so it’s safer and it could still allow us to analyse the data later to count the whales,” Dr Thums said. “We’re also hoping to get satellites tasked to capture high resolution images so we can compare the satellite data with LiDAR and, if it’s a good match, we might be able to rely on monitoring the Kimberley humpback whales with satellite in the future.”

The findings for the WAMSI Humpback project are expected to be released by early next year.

Related articles:

Whales from Space: Counting Southern Right Whales by Satellite PLOSONE

 

 

 

 

The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley. 

Category:

Kimberley Marine Research Program

Marine ecosystems considered in Kimberley survey

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Written by 

A multi-disciplinary team is closely monitoring the Kimberley’s coastal and estuarine environment to better understand how present levels of organic nitrogen and carbon play a role in sustaining marine productivity.

A team of Western Australian Marine Science Institution (WAMSI) collaborators from CSIRO, the University of Western Australia and The Australian Institute of Marine Science made two boat trips from King Sound to Walcott Inlet to identify information needed for monitoring water flow in the region.

The aim was to understand the role of organic materials in coastal ecosystems in order to safeguard the ecosystems against climate change and commercial development.

The project, led by CSIRO researcher Andy Revill, combined expertise in climate science and catchment rainfall-runoff modeling to better understand how inshore environments are sustained by terrestrial carbon and nutrient sources.

“It is pretty obvious the rivers are higher in nitrogen than the coastal environments,” Dr Revill says.

“One of the things we need to work out is where this organic nitrogen is actually coming from and what sort of transformations occur to this material.”

Future developments may upset delicate balance

While the Kimberley is among the most pristine environments in Australia, abundant water and energy resources will likely be developed in the near future which may have important implications for linked river, estuarine and inshore environments.

“We want to know what happens to material that is brought in with those fresh water streams and what role it will play in coastal production,” Dr Revill says.

He says the team worked on collecting critical information on linkages between terrestrial and marine ecosystems to find ways of minimising the impacts of climate change, catchment development and commercial or recreational fishing.

They collected data to estimate the annual freshwater run-off from rivers to coasts and the amount of organic matter supplied from the land to the coast.

They did this via a series of transects and measurements in the 40km-long Walcott Inlet.

Dr Revill says they monitored materials and water move through the inlet’s mouth.

“There was a big lag of tides between inside and outside which led to very large water movements in short spaces of time,” he says.

He says current data suggests an increased amount of land materials will start to move upstream.

The project team also had a sediment grab on board to monitor river and ocean bed material.

“We wanted to get a handle on how much material is coming off the catchment versus in-situ production,” Dr Revill says.

 

Category: 

Kimberley Marine Research Program

Researcher Q and A – Mari Carmen Pineda

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Published in AIMS Waypoint

Mari Carmen Pineda talks sponges, dredging and the link between science and industry.

Q1: What brought you to AIMS from Spain?

I first came to AIMS to work in ecology and microbiology and I fell in love with AIMS amazing facilities, like the National Sea Simulator (SeaSim) as well as the scientific excellence of the staff here.

Q2: You are currently studying sponges and how dredging effects them. Can you explain more?

I am working with the ‘sponge team’ I am sponsored by the Western Australian Marine Science Institute (WAMSI) Dredging Science Node to test how sponges respond to sedimentation and dredging-related pressures.

Q3: Sponges are sometimes said to be ‘a window’ into the effects of sedimentation? How is this so?

Sponges are an important component in marine coastal ecosystems where dredging activity usually occurs. In the WAMSI Dredging Science Node, we are working to determine the effects of dredging-related pressures (e.g. sedimentation, total suspended solids and light attenuation) on sponges.

We are performing a series of experiments within SeaSim to do this, in order to develop a better idea about how to devise sound environmental assessments related to dredging programs.

Q4: How do you think industry and science can help each other?

I think that following the global economic crisis it is essential that scientists engage with society and industry to make our research applicable to sustainable development.

Science and industry working together is so important. There are still huge gaps in our basic knowledge of marine systems, so we can’t forget that fundamental science is still essential in order to progress with our more applied research.

And this is what I love about my current job at AIMS! Studying the effect of a potential stressor such as dredging on an important group of marine invertebrates is basic research that can also be applied to improve sustainable dredging programs, ultimately benefiting our oceans, industry and our society.

Q5: Why do you think science is important generally?

Because I can’t conceive of a world without science! Can you? Science contains both the questions and the answers to the environment around us. Science enables us to better understand the world we are living in. Science has improved our health and our quality of life. I truly believe that science is the answer to our current and future problems. Science is our future!

Q6: Can you tell us one fascinating fact about the way in which people need sponges apart from in the bath?

Actually, sponges of the family Spongiidae (order Dictyoceratida, class Demospongiae) have traditionally been harvested as bath sponges, although now days most of the sponges we use in our tubs are actually synthetic!

Sponges have a lot to offer! Some sponge chemicals have considerable potential as anticancer drugs, for example.

Additionally, sponges provide important bioservices within their habitats, including nutrient cycling and the purification of vast water masses. These services provided by sponges ultimately affect the water quality of our oceans and the quality of our fisheries, which are directly linked to our health and wellbeing!

 

Category:

Dredging Science

El Niño to bring cool relief to WA waters

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Written by  (SNWA)

The widely publicised El Niño weather pattern set to cause dire warming conditions in eastern Australia this year is expected to have the opposite effect on WA waters.

The weather anomaly is tipped to cool WA coastal waters in the coming summer, bringing welcome relief to marine species battling to survive the current ocean heat.

WA coastal water temperatures are expected to drop by up to two degrees from ocean temperatures in the previous summers, which have been warmer than usual for the past few years.

The warmer ocean temperatures, which spiked up to five degrees higher than normal during an intense heat wave in 2010-11, have caused mass die offs in species ranging from corals and seagrass to crabs, abalone and scallops.

The effects were particularly severe in Shark Bay where warmer waters caused vast meadows of seagrass, which support whole ecosystems, to die off by 90 per cent in some areas.

Coral Bleaching at Rottnest Island (40m) in 2011. Credit: Damian Thomson, CSIRO

 

CSIRO Oceans and Atmosphere Flagship principal research scientist Ming Feng attributes the forecasted cooler waters to a weaker Leeuwin Current—the body of water that flows southwards from Indonesia down the WA coast bringing warm waters with it.

He says the El Niño weather pattern will weaken this current, therefore reducing the flow of warm water and cooling the ocean.

“This El Niño event will lower the strength of the Leeuwin Current and result in cooler ocean temperatures which will provide relief for a whole host of species,” Dr Feng says.

“But there will be winners and losers. Rock lobster (Panulirus cygnus) recruitment tends to be higher when ocean temperatures are warmer.”

Dr Feng says species such as finfish, seagrasses and corals will benefit from the cooler waters and associated stronger upwelling.

With persisted warm ocean temperatures in the central-eastern Pacific associated with the El Niño, ocean temperatures of the Western Australia coast start to cool. Credit: NOAA Climate Prediction Center.

 

He also expects to see a short-term change in species’ migration range, with warm-water species such as whale sharks (Rhincodon typus) remaining further north.

Dr Feng says the El Niño weather pattern causes a ‘see saw’ effect on ocean temperatures between the western Pacific and central-eastern Pacific, with oceans in the western Pacific cooling while oceans in the central-eastern Pacific warm.

He says El Niños occur irregularly, from every two years to one in seven, with the last El Nino occurring in 2009-10.

El Niños and their opposite, La Niñas, are thought to be becoming more extreme along with the effects of climate change.

The effects of the current El Niño are expected to remain until next summer.

 

Tropical fish usually found at Ningaloo Reef move south to feed on kelp forests

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By Bonnie Christian ABC News

A major climatic event has caused tropical fish that are usually found off Western Australia’s Ningaloo Reef to swim south to tackle seaweed forests off the Mid West coast, marine scientists say.

The fish are in such numbers and eating the kelp with a voracity not seen before anywhere else in the world.

A team of researchers from the University of Western Australia’s Oceans Institute has been studying the effects of a marine heatwave in 2011 on the temperate water ecosystem off Port Gregory.

Video

Tropical fish devouring kelp forests as they swim south in WA (ABC News)

“This is really quite novel globally,” Scott Bennett said.

“Never have we seen to this scale fishes just overgraze the seaweed forests like this so this is quite unique.”

The researchers translocated some kelp to a reef off Port Gregory during the study and then filmed how the fish responded.

Mr Bennett said the kelp was consumed within hours and at a rate that was on average three times higher than had previously been observed around the world.

 

 

He said there were a couple of factors contributing to the high numbers of typically tropical fish species being found further down the WA coast and the devastation to the kelp.

“Ever since 2011, when we had a really warm summer and marine heatwave off the Western Australian coast, we found that the kelps have disappeared from quite a few reefs around Port Gregory,” he said.

“At the same time as that we’ve had a lot of tropical fishes that eat seaweed come down the coast by the strong Leeuwin current.

“They’re now just grazing flat out on the reefs around Port Gregory and they’re stopping any kelp recovery so we’re seeing complete loss of kelp forests.”

Mr Bennett said the research is showing how extreme climatic events can effect marine ecosystems.

“The warming on its own, the kelp could possibly have recovered but the combination of the warming and the interaction between the kelp and the tropical fish from completely different ecosystems means we’ve got a fundamental shift in the nature of these ecosystems and it’s really difficult for them to recover now,” he said.

The UWA research has been tracking the interactions between the fish and the kelp for a number of years to monitor recovery and changes in the fish.

“Over the past three years we’ve had a really warm phase, each summer since 2011 has been some of the warmest on record,” he said.

“Now that’s sort of swinging back and we’re going into a bit of a cooler phase and the El Nino cycle begins again and we’ll see if this gives an opportunity for the kelp to recover.

“At the moment as long as those fish stick around, it looks like it’ll be quite difficult for the kelp forests.”

 

WAMSI Bulletin

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More news about WAMSI and its partners in the latest WAMSI Bulletin.

How can supercomputing help with marine science?

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There’s no doubt that Big Data is one of those concepts that is completely transforming the way we do research but what other capability does a facility like the Pawsey Supercomputing Centre have that can help marine science?

In June, the Pawsey Supercomputing Centre is offering a range of free short courses on supercomputing topics. WAMSI researchers, partners and friends are encouraged to consider taking advantage of the courses on offer or contact WAMSI Data Manager Luke Edwards to find out more about exploring the potential of the Pawsey supercomputing capacity. 

On 8-9 June, the sessions are aimed at those new to supercomputing (8th), and those wanting to understand more about using the systems (9th).  

The largest of these systems is Magnus.  It has over 35,000 cores, delivering in excess of 1PetaFLOP of computing power.  It is the most powerful public research supercomputer in the Southern Hemisphere and debuted at #41 in the Top500 list.  Marine researchers can apply for time on Magnus (details here).  Magnus and other supercomputers are designed for highly parallel distributed programs.   

Marine researchers who don’t have problems or software programs that can make use of Magnus should also be aware of the NeCTAR research cloud.  It enables researchers to create VMs (virtual machines), similar to Amazon Web Services, and deploy research tools and software without having to run their own physical servers. This dramatically reduces the overhead for researchers to run research applications while allowing them to scale up or down the amount of processing power required.

One of the important parts of the WAMSI program is to ensure the data collected through research is protected in the longer term and held in a place where it can be accessed both for management and planning purposes.

WAMSI Data Manager Luke Edwards, is based at the Pawsey Supercomputing Centre.  Its huge data storage capacity is available not just for radio astronomers linked to the Square Kilometre Array, but all researchers, including marine researchers.

With greater than 40 Petabytes of data storage available, researchers are encouraged to apply for storage if they have more than 5Tbs of data.  The aim of the storage is to facilitate sharing and collaboration with research partners.  To discover more about how to apply for storage visit here.

The Pawsey Supercomputing Centre Visualisation team can also provide a package of hardware, software and expertise that can assist marine researchers.

Applying visualisation techniques to difficult datasets can require specialist hardware, which can include high end graphics cards for handling large datasets in real-time, novel display technologies to fully exploit the human visual system, and user interface devices to facilitate the interaction.  To find out more visit here.

“The big question raised by researchers is how do I best document my data so in ten years’ time (WAMSI 4), I can use all this great data from the Kimberley and the Dredging Node,” Mr Edwards said.

Source: http://imgs.xkcd.com/comics/documents.png

“It’s the simple stuff that is the key to good data management, like making sure you have good conventions for file names and complete metadata,” he said. 

WAMSI has a requirement that all data is made publicly available and therefore it’s important that its researchers make it discoverable through creating metadata.

“The big mistake researchers can make is to start off with a little bit of data not thinking they’ll need formal data management,” Mr Edwards said. “They might think they can handle it and back it up on a portable hard drive. But as the project continues and you incrementally collect more data, problems get bigger and bigger and then at the end of the project there’s a massive problem and it’s really inefficient to go back through that data. Managing it correctly from the start is much more efficient.”

There are four main reasons to implement good data management:

Risk Management

Data security is important.  Backing up data, which is a major asset for any project, is an important risk management strategy.  Managing risk in relation to sensitive data, privacy issues, Intellectual Property and private industry data is also important.

Transparency 

Transparency is about protecting yourself. Some climate scientists, for example, have had to deal with people suggesting that they’re making up their work, that it’s a big conspiracy. Having all your data readily accessible and discoverable ensures transparency and defends you again unfounded accusations.

Exposure

Studies now show that researchers who make their data open get more exposure and get more citations.

Mandate

It’s becoming more of a mandate by funders like WAMSI and peer reviewed journals are requiring data to be made publicly accessible.

Data management at WAMSI

In terms of the workflow, when the WAMSI project is finished or almost complete, that data must be deposited either in the Pawsey Data Portal or the CSIRO or AIMS data centre. Once that’s done and the metadata is finalised there’s an 18 month embargo period. So once data has been deposited it gives the researcher time to write up papers for publishing before that data is then made public.  

WAMSI data management workflow

“So it’s all about how do I discover this data and how do I access this data,” Mr Edwards said. “The idea is to create metadata, which feed into the national infrastructure so you should eventually be able to do a Google search for the ‘Kimberly WAMSI data’ and then Google should come up with the website where the data can be accessed.

Pawsey data portal page for WA Node Ocean Data Network

How is it being used?

From the raw data there is good functionality through the Pawsey data portal that researchers can use. Some researchers are already using it for collaboration with restricted access.

Big data analytics enable us to find new cures and better understand and predict the spread of diseases. Police forces use big data to catch criminals and even predict criminal activity and credit card companies use big data analytics it to detect fraudulent transactions. A number of cities are even using big data analytics with the aim of turning themselves into Smart Cities, where a bus would know to wait for a delayed train and where traffic signals predict traffic volumes and operate to minimize jams.

Why is it so important?

The biggest reason big data is important to everyone is that it’s a trend that’s only going to grow.

As the tools to collect and analyze the data become less and less expensive and more and more accessible, we will develop more and more uses for it.

And, if you live in the modern world, it’s not something you can escape.

For researchers, being FAIR (Findable, Accessible, Interoperable and Reusable) will ensure it doesn’t go to waste.

 

This article is based on a presentation given by Luke Edwards at the 2015 WAMSI Research Conference

The good-news El Niño story for Western Australia’s oceans

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By Jaci Brown, Madeleine Cahill, Ming Feng and Xuebin Zhang, CSIRO The Conversation.

While eastern Australia trembles at the impending El Niño this year, potentially increasing heat waves and bushfires, the coastal waters of Western Australia (WA) would find El Niño a welcome relief from the heat.

In the summer of 2010-11 WA’s oceans were struck by devastating marine heatwaves, with temperatures rising up to 5C above average, causing mass deaths of marine life and coral bleaching.

Temperatures have remained warm since, due to the lingering effects of the large 2010-11 La Niña. But El Niño could be the relief these waters need for marine life to recover.

Why is the water so warm?

The water temperature off the WA coast is determined largely by the Leeuwin Current, which flows south along the WA coast from Indonesia. The Leeuwin Current is unique in the world as it is the only subtropical poleward-flowing boundary current on the eastern side of an ocean basin.

Most coastal currents, such as the East Australian Current and the Gulf Stream, are found on the western side of ocean basins.

The Leeuwin Current occurs because of the “gap” between Australia and Indonesia that connects the Pacific and Indian Oceans. The easterly winds over the Pacific Ocean pile warm water up on the western side of the ocean basin. This increases the sea level through the Indonesian archipelago. The high sea level signal is then transferred down the coast of WA, creating pressure gradients that draw in warm water and push it southward, forming the Leeuwin Current.

Satellite map of south west Australian coast with red colouring off the western coast, green and yellow colours elsewhere
A composite satellite image of sea surface temperature anomalies in July.
The Leeuwin Current can be identified as a narrow band of warmer water adjacent to the coast. Image: CSIRO

The easterly winds over the Pacific Ocean vary over time, being stronger in La Niña years and weaker in El Niño. The changing wind strength alters the amount of water piled up in the west of the Pacific and hence the sea level near Indonesia: higher in La Niña years and lower in El Niño. The changing sea level then influences the strength of the Leeuwin Current.

La Niña drives marine heatwaves

In a La Niña year, a stronger-than-normal Leeuwin Current forms off the northwest coast and flows southward, finally wrapping into the Great Australian Bight, extending to the west coast of Tasmania. The current also means warmer-than-normal water is transported further south along the WA coast, so temperatures are higher. In an El Niño year, the current weakens, and ocean temperatures fall.

La Niña drove the 2010-2011 marine heatwave (as well as the exceptional flooding in eastern Australia). Warm water has been flowing in the Leeuwin Current since 2010 without the usual reprieve brought from El Niño events.

 

Sea level anomaly 2010-2015

The warm water has led to extensive coral bleaching along with flooding and damage to sea grasses. Species along the coast of southwestern Australia are used to living in cooler temperate waters, and the heat wave resulted in mass deaths for a wide range of species.

Coral reef with white coral sections and fish above
Coral Bleaching at Rottnest Island (40m) in 2011. Photo taken by Damian Thomson, CSIRO.

How will El Niño alter the Leeuwin Current this year?

An El Niño has been forecast for this year and the easterly winds over the Pacific ocean have weakened. As a result satellites are already detecting a lower than normal sea level signal in the western equatorial Pacific.

Sea level map for March 2015 from satellite data. Blue areas near Indonesia show sea levels are lower then normal. AVISO
Sea level map for March 2015 from satellite data. Blue areas near Indonesia show sea levels are lower then normal. AVISO

 

A typical measure of El Niño is the Nino3.4 index which measures sea surface temperatures in the Pacific Ocean. The Nino3.4 index is very strongly correlated with sea level in the western equatorial Pacific.

Sea level at Fremantle is a good indicator of the strength of the Leeuwin Current. It tends to follow the Nino3.4 index and western equatorial sea level observations but with a delay of a few months. This few month delay is the time taken for the sea level change in the western Pacific to influence the strength of the Leeuwin Current near Fremantle.

Given that an El Niño has been forecast for 2015 and the sea level is dropping in the western Pacific, it seems very likely that we will see a weakening in the Leeuwin Current and cooler water temperatures along the coast of WA.

Graph with lines tracking up and down representing sea level
Timeseries of Nino3.4 (a measure of the El Niño and La Niña variability) compared to sea level in
the western tropical Pacific and sea level at Freemantle (a measure of the strength of the Leeuwin current)
 
So while eastern Australia watches for heat and drought, El Niño could be the cool relief WA’s oceans have been waiting for.

The Conversation

 

Jaci Brown is Senior Research Scientist at CSIRO.
Madeleine Cahill is Oceanographer at CSIRO.
Ming Feng is Principal research scientist, Oceans and Atmosphere Flagship at CSIRO and WAMSI.
Xuebin Zhang is Senior Research scientist, Sea level rise at CSIRO.

This article was originally published on The Conversation.

Video: Understanding ENSO

This Bureau of Meteorology video explains what El Niño–Southern Oscillation (ENSO) is, how the cycle works including the science behind the phases, and the potential impacts on Australia’s climate and weather.