A mix of science and culture to snag seagrass rescue in a world heritage site

Dr Elizabeth Sinclair, School of Biological Science and Oceans Institute, University of Western Australia and Patricia Oakley, Malgana Elder, Ranger, and Indigenous Knowledge holder

Please be advised that the following article contains images of an Indigenous person who has died, which are used with family permission.

Yandani Gathaagudu, Shark Bay, Western Australia

Gathaagudu sits at the western most point in Australia. It is the Traditional lands of the Malgana Peoples who have inhabited the region for the last 30,000 years. Much of Malgana Country is now Sea Country. The sandy dunes were flooded when the sea level rose at the end of the last ice age. During the following millennia, the seagrass expanded over the drowned sand dunes, creating new meadows. The meadows formed banks and sills in the shallow waters. They slowed the tidal water flow and it became saltier because the evaporation rate is higher than rainfall. The seagrass banks in the eastern gulf eventually created Hamelin Pool (Figure 1), home to some of the worlds earliest life forms – the Stromatolites, living rocks, or Ganthurri maya – home of the Malgana ancestors.

Gathaagudu is a meeting point for warm and cool water species, so there are lots of different plants and animals in the Bay. Some are permanent residents and others visit seasonally. Did you know that there are 28 species of shark (thaaka) in the Bay? The uniqueness of Shark Bay was globally recognised in 1991 with the declaration of a UNESCO World Heritage Site based on its environmental values.

Figure 1: Living stromatolites, very similar to 3.5 billion year old fossils, live in Hamelin Pool as seagrass banks maintain high salinity levels necessary for survival. Photo Elizabeth Sinclair

What are seagrasses and why are they so important?

Seagrasses (or wirriya jalyanu in Malgana language) naturally inhabit shallow coastal waters around the globe, except Antarctica. So, next time you go diving or snorkelling, have a closer look at the wondrously long, bright green ribbons, waving with the ebb and flow of water. They are seagrasses– marine plants which have flowers, fruit, and seedlings, just like their land-based relatives we know as grasses. Lots of critters live in, on, and around them. About 12 species of seagrass live in the crystal clear, salty waters of Shark Bay, from the tiniest paddle weeds (Halophila spp.) less than 1cm tall, to the largest ribbon weed (Posidonia australis) with leaves up to 1m long and 2m tall stands of wire weed (Amphibolis antarctica) (Figure 2).

Seagrasses protect our coastlines from storm damage, store large amounts of carbon in their leaves, rhizomes, and sandy sediment beneath them. They also provide habitat and food for wildlife. Conserving and restoring seagrass meadows has a vital role in climate change mitigation and adaptation. It’s much easier to protect and conserve this natural ecosystem than to try and restore it.

Figure 2: Two large temperate seagrasses in Gathaagudu: (left) Ribbon weed meadow (Posidonia australis); (right) Wire weed meadow (Amphibolis antarctica). Photos Rachel Austin and Matt Fraser, UWA.

How many different plants make up a seagrass meadow?

Can you imagine trying to count the number of grass plants in a backyard lawn? It’s too hard to trace all the rhizomes and roots to answer that question, plus it would kill the grass. Luckily, all living organisms have unique DNA code (unless you are identical twins). Therefore, it is possible to look at the DNA to find out whether a seagrass meadow has grown from a single plant (or clone) or there are many different individual plants growing together. It’s possible to collect shoot samples and look at the DNA. We did this from across Shark Bay, in waters from normal ocean salinity to almost twice as salty – that’s very salty. We studied 18,000 genetic markers to show most of our ribbon weed shoots were identical. That is, they were from a single plant that had expanded over 180 km, making it the largest known plant on Earth. It is challenging to determine the exact age of a seagrass meadow, but we estimate the Shark Bay plant may be 4,500 years old, based on its size and growth rate. Seagrass meadows in other places contain lots of different plants growing together.

Climate change and seagrasses

‘We are all connected – people and the environment.’ What we do on the land has an impact on what happens in our rivers and oceans. Seagrasses are not immune from climate change impacts: warming ocean temperatures, ocean acidification and extreme weather events are a significant challenge for them. In 2010-11, an extreme marine heatwave occurred along the Western Australian coastline. The seagrass was badly damaged in the Bay (Figure 3). The death of seagrass then affected the health of many culturally significant species, from the sea mullet (Mugil cephalus, mulgarda), nesting cormorants (Phalacrocorax varius, wanamalu), dugongs (Dugong dugon, wuthuga) and green turtles (Chelonia mydas, buyungurra). Some species lost their homes, while others went hungry. Climate change is the single largest threat to the health of Shark Bay.

Figure 3: (left) A dead wire weed meadow following the 2010/2011 heatwave event, (right) becomes overgrown by algae. Photos Matt Fraser, UWA

Knowledge sharing workshops for seagrass restoration - Healthy Country, Healthy People

A Shark Bay ecosystem without large temperate seagrasses would look very different. Many species would no longer survive, and other tropical species would move in through a process known as ‘range shifting’. Cool water species would effectively shift their distribution to cooler, higher latitude waters. We (University researchers and Traditional Owners) learned we had a common goal: to look after Sea Country. Restoring (seagrass) ecosystems and conserving biodiversity are ‘western science speak’ and are part of a global solution to manage the impacts of climate change. These concepts are also at the core of Malgana culture and lore. ‘If we look after country, then Country will look after you’

Researchers and Malgana Aboriginal Corporation Rangers partnered to share knowledge of Country and develop methods to restore seagrass. We demonstrated through field-based workshops that seagrass meadows can be restored using simple, effective methods - planting cuttings and using seagrass snaggers. We also learned it will take at least 10 years to establish mature meadows which have similar biodiversity and carbon sequestration rates to natural undisturbed seagrass meadows.
Working with Rangers on Country provided opportunities for employment, obtain academic qualifications and connection of reconnection with Country as many Malgana Peoples do not live on Country. ‘Being on Country is medicine for us’

So what is a seagrass snagger and how does it work?

A seagrass snagger is a sand-filled hessian sock or tube (Figure 4). The idea is simple. When seagrass meadows have died and no leaf canopy is visible, wire weed seedlings dispersing in the waters during winter months have nothing to attach to. The rough hessian material acts as a natural fibre for seedlings to attach to using their ‘grappling hooks’. The hessian decomposes over 1-2 years, long after the seedling has grown a new root and become anchored in the sandy sea floor. The snaggers come in different sizes – small brick and long snaggers. This is a great activity to generate participation by citizen scientists.

Figure 4: (top left) A pile of sand filled snaggers; (bottom left) Malgana ranger Nicholas Pedrocchi (deceased) and UWA researcher Dr John Statton lower a seagrass snagger into the water; (right) Wire weed seedling anchored onto a snagger using its grappling hook. Photos Elizabeth Sinclair, UWA

Communication is key

Knowledge sharing with local communities is an important part of communication. Generating a sense of participation and community spirit to come on a restoration journey. An ‘Art meets Science’ themed Wirriya Jalyanu (seagrass) Festival (https://www.seagrassresearch.net/festival) marked the end of our project funding. The festival shared knowledge of Sea Country through a mix of science, culture, language, and artistic activities for all ages (Figure 5). Sharing this knowledge with the wider community improved their understanding of this globally recognised IUCN World Heritage Area.

Figure 5: Community glass artwork by Shark Bay Arts Council members of restored seagrass meadow on display at the Wirriya Jalyanu (seagrass) Festival. Photo Elizabeth Sinclair, UWA