Just like birds and mammals carrying seeds through a rainforest, green sea turtles and dugong spread the seeds of seagrass plants as they feed. Our team at James Cook University’s TropWATER Centre has uncovered a unique relationship in the seagrass meadows of the Great Barrier Reef.
We followed feeding sea turtle and dugong, collecting samples of their floating faecal matter. Samantha then had the unenviable job of sifting through hundreds of smelly samples to find any seagrass seeds. These seeds range in size from a few centimetres to a few millimetres, and therefore can require the assistance of a microscope to be found. Once any seeds were found, they were stained with a chemical dye (Tetrazolium) to see if they were still viable (capable of growing).
Why is this important for turtles and dugong?
Green sea turtles and dugong are iconic animals on the reef, and seagrass is their food. Dugong can eat as much as 35 kilograms of wet seagrass a day, while sea turtles can eat up to 2.5% of their body weight per day. Without productive seagrass meadows, they would not survive.
This relationship was highlighted in 2010-11 when heavy flooding and the impact of tropical cyclone Yasi led to drastic seagrass declines in north Queensland. In the year following this seagrass decline there was a spike in the number of starving and stranded sea turtles and dugong along the entire Queensland coast.
The seagrass team at James Cook University has been mapping, monitoring and researching the health of the Great Barrier Reef seagrasses for more than 30 years. While coral reefs are more attractive for tourists, the Great Barrier Reef World Heritage Area actually contains a greater area of seagrass than coral, encompassing around 20% of the world’s seagrass species. Seagrass ecosystems also maintain vibrant marine life, with many fish, crustaceans, sea stars, sea cucumbers, urchins and many more marine animals calling these meadows their home.
These underwater flowering plants are a vital component of the reef ecosystem. Seagrasses stabilise the sediment, sequester large amounts of carbon from the atmosphere and filter the water before it reaches the coral reefs. Further, the seagrass meadows in the Great Barrier Reef support one of the largest populations of sea turtles and dugong in the world.
Seagrass meadows are more connected than we thought
Samantha’s research was worth the effort. There were seeds of at least three seagrass species in the poo of both sea turtles and dugong. And lots of them – as many as two seeds per gram of poo. About one in ten were viable, meaning they could grow into new plants.
Based on estimates of the number of animals in the coastal waters, the time it takes for food to pass through their gut, and movement data collected from animals fitted with satellite tags, there are potentially as many as 500,000 viable seeds on the move each day in the Great Barrier Reef. These seeds can be transported distances of up to 650km in total.
This means turtles and dugong are connecting distant seagrass meadows by transporting seeds. Those seeds improve the genetic diversity of the meadows and may help meadows recover when they are damaged or lost after cyclones. These animals help to protect and nurture their own food supply, and in doing so make the reef ecosystem around them more resilient.
Understanding recovery after climate events
This research shows that these ecosystems have pathways for recovery. Provided we take care with the environment, seagrasses may yet recover without direct human intervention.
This work emphasises how much we still have to learn about how the reef systems interconnect and work together – and how much we need to protect every part of our marvellous and amazing reef environment.
Samantha J Tol, PhD Candidate, James Cook University; Alana Grech, Assistant Director, ARC Centre of Excellence for Coral Reef Studies, James Cook University; Paul York, Senior Research Scientist in Marine Biology, James Cook University, and Rob Coles, Team leader, Seagrass Habitats, TropWATER, James Cook University
On May 10, the 43.5-metre schooner Avontuur arrived in the port of Hamburg. This traditional sailing vessel, built in 1920, transported some 70 tonnes of coffee, cacao and rum across the Atlantic. The shipping company Timbercoast, which owns and operates Avontuur, says it aims to prove that sailing ships can offer an environmentally sustainable alternative to the heavily polluting shipping industry, despite being widely seen as a technology of yesteryear.
Similar initiatives exist across the world. In the Netherlands, Fairtransport operates two vessels on European and transatlantic routes. In France, Transoceanic Wind Transport sails multiple vessels across the English Channel and Atlantic Ocean, and along European coasts. The US-based vessel Kwai serves islands in the Pacific. And Sail Cargo, based in Costa Rica, is building Ceiba, a zero-emission cargo sailing ship.
These initiatives have an environmental objective: transporting cargo without generating greenhouse gas emissions. But are they really a viable alternative to today’s huge fossil-fuelled maritime cargo transport industry?
Shipping emission targets?
On April 13, 2018, the International Maritime Organization, the United Nations body that regulates shipping, agreed for the first time to limit the sector’s greenhouse emissions. It’s targeting a 50% reduction by 2050 (relative to 2008 levels), with the aim to phase out emissions entirely.
This was a breakthrough, given that both the 1997 Kyoto Protocol and the 2015 Paris Agreement exclude international shipping (and international aviation) from emissions targets, because these are so hard to attribute to individual countries.
Conventional seaborne cargo transport is relatively energy-efficient. It emits less greenhouse gas per tonne-kilometre (one tonne of goods transported over one kilometre) than transport by train, truck or plane. But because 80-90% of all goods we consume are transported by sea, the total emissions of the shipping industry are immense.
According to figures from the International Maritime Organization (IMO), shipping accounts for 2-3% of global emissions – outstripping the 2% share generated by civil aviation.
As the global demand for goods increases, so does the need for shipping. As a result, the IMO has projected that the sector’s greenhouse emissions will grow by anything between 50% and 250% between 2012 and 2050, despite improvements in fuel composition and efficiency. More worryingly, a commentary on that report in Nature Climate Change warns that “none of the anticipated shipping scenarios even approach what is necessary for the sector to make its ‘fair and proportionate’ contribution to avoiding 2℃ of warming”.
A recent report commissioned by the European Parliament raises further alarm bells, underscoring the fact that the sector’s huge growth is likely to swamp any carbon savings that come from improved operations. On top of this, the significant progress made in other industries means that the relative share of greenhouse gas emissions from cargo shipping is likely to increase from the current 2-3% to 17% by 2050.
The OECD International Transport Forum is less pessimistic. It projects a 23% increase in the sector’s emissions between 2015 and 2035 on current trends, but also argues that it will be possible to decarbonise maritime transport altogether by 2035, through the “maximum deployment of currently known technologies”.
These emissions-reducing propulsion technologies include kites, solar electricity, and advanced sail technology. Some of them, such as Flettner rotors, are already in use. But these will not be scaled up and become viable unless there is strict regulation, even if some shipping companies have taken steps to reduce their emissions ahead of a binding IMO target. Electricity-propelled container barges operate in Belgium and the Netherlands.
Meanwhile, the IMO faced a tricky balancing act in juggling the priorities of different countries. Climate-vulnerable nations such as the Marshall Islands want shipping emissions to be cut entirely by 2035. The European Union has proposed a reduction of 70-100% by 2050, while emerging economies such as Brazil, Saudi Arabia and India have argued against any emissions target at all. Despite these differences, the IMO did agree on a 50% reduction target by 2050 in April 2018.
It took Avontuur 126 days to sail from France to Honduras, Mexico, Cuba and home to Germany. But conventional container ships can cross the Atlantic in about a week. Avontuur was carrying more than 70 tonnes of cargo on arrival in Germany. But many cargo vessels now carry more than 20,000 standard shipping containers (TEU), each weighing more than 2 tonnes and able to hold more than 20 tonnes of cargo.
Given the relatively small capacity of sailing ships, it is expensive and labour-intensive to ship cargo this way. But despite these limitations, support for sail cargo initiatives is growing. A consortium of small North Sea ports, for example, will “create sail cargo hubs in small ports and harbours, giving local businesses direct access to ethically transported goods”.
These initiatives signal the revival of sail cargo with an explicit environmental agenda, although this effort is dwarfed by the scale of the global shipping industry. But while they don’t stack up in logistical terms, these voyages can help us see the possibilities for a world without fossil fuels. Sail cargo aims to rethink not only the means of propulsion for cargo vessels, but the entire scale, economy and ethics of cargo transport.
Traditional sailing vessels like Avontuur will not be able to compete with conventional cargo vessels on speed, scale or cost. But they help us focus on the underlying issue. We ship too much, too often and too far. The scale of shipping is unsustainable. That is why we need a change of mindset as much as a change of technology.
Sail cargo initiatives raise awareness about the devastating environmental effects of conventional cargo shipping. And they do so by showing that an alternative is possible. Indeed, it has been around for thousands of years.