An unusual summer for Fleurieu seagrass

The Seeds for Snapper seagrass restoration project has wrapped up for the season. While aiming to restore seagrass in Encounter Bay, a lack of seagrass fruit this season meant the project team had to change tack – but all is not lost as the learnings were an invaluable step towards gaining a better understanding of this unique plant life.

In a ‘normal’ season, the project involves local volunteers combing the beaches and near shore waters for seagrass fruit. Collected fruit (that carry and protect a single seed) are stored in holding tanks, before being propagated into sandbags and returned to the sea floor of Encounter Bay, aiming to reproduce and create boundless underwater meadows of seagrass. It’s an important measure to help mitigate the risks faced by vulnerable and diminishing seagrass meadows, including land-based impacts such as pollution and stormwater discharge, as well as rising sea temperatures and storm surges.

Seagrass is a vital element of marine ecosystems with underwater meadows providing several environmental benefits, including carbon sequestration and providing important foraging and nursery grounds for baby pink snapper, whiting, blue swimmer crabs, prawns, King George whiting, garfish and squid. They are also critical habitat for many other fish and invertebrate species such as the region’s iconic leafy and weedy seadragons.

Landscapes Hills and Fleurieu Coast and Marine Officer Caroline Taylor explained more about the unusual events that re-wrote the script this year.

“The Fleurieu Peninsula Seeds for Snapper project has had a very unusual summer. The Posidonia seagrass did not set fruit within Encounter bay to Goolwa area for the first time in recent years.

“It’s difficult to pin-point an exact cause, but we can likely put it down to a couple of factors. Firstly, the high and prolonged flow from the River Murray flooding, which caused high turbidity and sediment deposition for extended periods (reducing sunlight to plants). A cooler and more overcast summer meant we also experienced lower summer water temperatures (3-4 degrees below average), which are known to effect seagrass. A strong Great South Australian Coastal Upwelling from Antarctic waters has likely further added to the situation.

“Seagrass along the Adelaide metropolitan coast provided ample fruit for the Adelaide based Seeds for Snapper project, however couldn’t be used on the Fleurieu due to being of different local provenance and outside of natural fruit dispersal areas,” she said.

The project had also aimed to deploy some of the seagrass sandbags around the well-known South Australian shipwreck at Yilki. While seeded sandbags couldn’t be deployed, trials were undertaken to test the longevity of the bags at the site. OzFish Unlimited volunteers were recently involved in a sandbag trial at the wreck site, with the help of DEW’s Maritime Heritage and Coast and Marine branches and Flinders University. This trial will help to determine the longevity of the sandbags at the wreck site, which endures high turbulence, and will inform the project team for next summer’s seagrass restoration efforts, when fruit is expected to return to the Fleurieu south coast.

“While this year’s project outcomes didn’t quite come to fruition, the team has learnt a lot about the variability of fruiting habits of Posidonia seagrass and will apply this science to future restoration projects,” Caroline said.

Learn more about Seeds for Snapper on the project page.

The ‘Seeds for Snapper’ project is part of OzFish Unlimited’s national seagrass restoration program, funded on the Fleurieu Peninsula by Landscapes Hills and Fleurieu and BCF with support from Department for Environment and Water, Flinders University, SARDI Aquatic Sciences, local councils and community volunteers.