Why is Seagrass so Important to the Great Barrier Reef?

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When most people think of the Great Barrier Reef they probably imagine an amazing array of colourful fish and coral with the odd shark or turtle thrown in. And yet there is so much more to learn about this enormous ecosystem.  

Mangroves and seagrass beds may not be the most glamorous part of the Great Barrier Reef but they are both vital to its health and livelihood.

Rob Coles and Samantha TolMarine biologists come here from all over the world to research different aspects of this enormous marine ecosystem.

Recently, Travel NQ was invited to join two researchers from James Cook University, Dr Rob Coles and Samantha Tol, on a trip to Green Island, near Cairns.

I wanted to find out more about the important role that seagrass plays in the overall health and wellbeing of the reef and the research work they are conducting.

Seagrass and the environment

Let’s start with the big picture.

Globally, seagrass meadows are in decline, largely due to the impact of humans. Chemical run-off from the land and over-fishing are two factors contributing to the decline.

Locally in North Queensland, recent research shows that seagrass meadows between Cairns and Cardwell have been deteriorating as a result of recurring cyclones and bad weather.

Seagrass plays an important role in the ecosystem of the reef since it is an important food source for various species including sea turtles and dugongs (manatees).

It also acts as a fish nursery, helps stabilise sediment and plays a role in water clarity.

Jennie Gilbert tickling one of her turtle patientsThe most obvious concern from declining seagrass is the affect on marine life such as turtles. Many turtles brought into the rehabilitation centre in this area are starving.

Role of climate change

While sceptics question whether climate change is even happening, we know one thing – warmer temperatures in the tropics means more cyclones.

Far North Queensland has experienced several severe cyclones over the past few years and it has impacted our seagrass.

James Cook University’s TropWATER researcher Dr Rob Coles, says that seagrass meadows close to well-populated coastal areas seem to be the most affected and climate change is playing a big part.

“The more intense the storms and cyclones are, the harder it is for seagrass to grow back as it needs light and sunshine to grow,” he says.

He explains that seagrass has two seasons and normally grows between September through to March, with a dormant sleeping period called the ‘senesent period’ from April through to August.

However, if there isn’t enough sunshine during the growing period, seagrass meadows don’t regenerate as quickly as they should.

The concern is that if these meadows don’t grow back in abundance, we could see a decline in turtle and dugong numbers, as well as the wider ecology of the Great Barrier Reef.

Seagrass in the food chain

seagrass research on green islandSeagrass leaves only have a lifespan of about two weeks before they die and new growth begins.

During this short lifespan they are either eaten by turtles, dugongs and fish, or they break away and float off or the become buried in sediment.

Feeding patterns are also different among seagrass eaters.

Sea turtles tending to sit lazily in the seagrass and nibble and trim the tops off the grass while dugongs leave a trail as they put their noses to the bottom and dig out the roots with their nose. They are messy eaters and grass fragments float away around them.

Sea Grass Great Barrier ReefResearch is currently underway by James Cook University PHD student Samantha Tol, as to whether or not seagrass fruits eaten by dugongs can germinate from the seeds excremented by the dugongs.

These findings could be vital in better understanding seagrass renewal and dispersal.

Seagrass research

Rob has been mapping seagrass in this area since 1987 and his maps are still used today by the Marine Park Authority, so he is considered somewhat of an expert when it comes to this topic.

green island seagrass bedsRob and his TropWATER team monitor up to 45 coastal sites every year to observe the density of seagrass beds and any changes that may be occurring.

I recently went with Rob and Samantha to Green Island, off Cairns, to observe as they did their research. I wanted to find out more about their research and to see the seagrass meadows firsthand.

While there are actually 72 species of seagrass worldwide, only 15 species are in Queensland and 11 of them in the Cairns region.

Luckily, while seagrass meadows are in decline in the region, Green Island has not been affected by the bad weather in Far North Queensland and the island is home to nine different species of seagrass growing in abundance.

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