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The Lowdown on Seagrass

The Lowdown on Seagrass

They have grassy leaves, but they are not true grass, and they are found in marine environments. What are they?

Seagrass are so named because most have ribbon- like grassy leaves. These plants often grow in large “meadows” which look like grassland in brackish or marine environments. But other kinds of seagrass do not look like grass at all; some may have oval or paddle-shaped leaves.

Seagrass are different from algae as they have roots and horizontal stems that are often buried in sand or mud. These roots anchor the seagrass, and absorb nutrients. Their leaves are usually green, and contain veins and air channels that carry fluid and absorb gases. These plants also form flowers, fruit and seeds, and they reproduce by pollination, where the pollens are transported to other plants by water.

What is an amazing fact about seagrass is that, while they live in water, they do rely on light to convert carbon dioxide into oxygen. This process, called photosynthesis, allows the production of oxygen that is available for use by other organisms.

There are currently 58 known species of seagrass in the world, and around 30 of which can be found in Australia. They are mainly found in bays, estuaries and coastal waters from the mid-intertidal (shallow) region down to depths of 50 or 60 metres. Most species are found in shallow inshore areas.

On the Gold Coast, there have been seven species of seagrass recorded in recent survey efforts that include: Zostera muelleri, Halophila ovalis, Halophila decipens, Halophila spinulosa, Cymodocea serrulata, Syringodium isoetifolium and Halodule uninervis.

Seagrass on the Gold Coast are thriving fish habitats, as well as a source of food. In the Broadwater, seagrass “meadows” are home to juvenile fish and tiger prawns. Green turtles and dugongs (sea cows) in Gold Coast waters depend on seagrass for food. A turtle can eat 2kg per day, while a dugong can eat a whopping 28kg per day!

Surveys on seagrass in Gold Coast waterways are conducted by Gold Coast Seagrass. This group is part of a worldwide organisation called Seagrass Watch Global, but the 10-year old Gold Coast survey group is independently managed, with funding from Queensland Wildlife Parks Association. The group is also part of the Gold Coast Catchment Association’s Citizen Science program, and works closely with the Catchment Unit of the Gold City Council.

Photos by Gold Coast Catchment Association

More than 20 surveys have been conducted since the Seagrass Watch re-launch in September 2018. The group has identified 14 50m-by-50m sites, of which seven are currently active – Tallebudgera Creek, Wave Break Island sites 2 and 3, South Stradbroke Island sites 1 and 2, Crab Island, and Loders Creek.

Lauren Morgan, coordinator of Gold Coast Seagrass explains, “Surveys are done by volunteers, most of whom have no scientific background. We provide onsite training for the volunteers, based on the worldwide standardised program.”

The surveys are conducted during three seasons within the year: March-April, July-August, and October-November. The volunteers conduct at least one survey per site per season.

“We conduct surveys in the right conditions,” says Lauren. “Low tide is the perfect time as the seagrass are clearly visible for observation. We conduct species identification and quantify the seagrass per quadrant. We also share the data we gather with government agencies. The information gathered from surveys also serve as warning systems for these government agencies relevant to water health and conditions.”

Aside from seagrass, the group also monitors sea turtle and seahorse presence in the survey areas. The Seagrass Gold Coast program raises community and government awareness in the region, aiming to distribute information on seagrass and its ecological value.

“Through the seagrass monitoring programs, we are able to take people out and educate them about the value of seagrass. For instance, they learn that the seagrass uptake of carbon dioxide is the same as that of mangroves. We also see other wildlife, that’s why we include an ID guide for seahorse, sea turtle and migratory birds,” explains Lauren.

Seagrass are very sensitive to water quality and are subjected to sedimentation. As they need light to survive, it is important that the water in the areas where they grow remain clean.

Many factors affect the health of seagrass. Urban runoff, coastal development, sedimentation, and increased presence of macroalgae (seaweed) affect the survival of seagrass meadows. While general boating activities also affect seagrass through boat strike, particularly in the shallow areas, Lauren advises that if boaties are mindful of the presence of seagrass, they may be able to avoid

damaging seagrass meadows. Recreational fishing is also affected by the health of seagrass, as these “grassland” areas are safe habitats for juvenile fish.

Gold Coast Seagrass encourages everyone in the community, including the recreational boating and fishing communities, to be part of this citizen science program. Having volunteer site champions will definitely help in the sustainable monitoring of the seagrass around the Gold Coast.

Healthy waterways allow us to enjoy recreational activities safely, and more importantly, they allow our environment and wildlife to thrive. The “lowly” seagrass are an amazing plant life that are crucial to healthy marine ecosystems. Without seagrass in our waters, we will not have fish, dugongs, or turtles in there either.

If you want to know how boaties can help the seagrass surveys, email gcseagrass@gmail.com or visit goldcoastcatchments.org/seagrass/

 

By Roselle Tenefrancia

 

(Published in the Oct-dec 2019 edition)