November 6, 2020

wire weed seagrass seedlings floating in teh water at Shark Bay
Wire weed (Amphibolis antarctica) seedlings spend several weeks to months floating with the currents and tides, before eventually sinking to the seafloor and catching hold of something to grow on. Image: Rachel Austin

University of Western Australia (UWA) researchers and Malgana Rangers conducted a joint workshop in August as part of a Marine Biodiversity Hub project to assist the natural recovery of seagrasses at Shark Bay.

In this final of four workshops, the researchers and rangers worked on developing and trialling seagrass recovery techniques. The rangers also completed their conservation and land management training, which includes seagrass habitat restoration.

The Shark Bay World Heritage Site is known as Gathaagudu (two waters) to Malgana Traditional Owners. This region experienced an unprecedented heat wave in the summer of 2010–2011. Sea-surface temperatures spiked 2–5°C above long-term averages, devastating more than 1300 km2 of dense seagrass meadows.

Widespread loss of food and habitat caused declines in many species. Some of the species affected are culturally significant, including green sea turtles (Buyungurra), dugong (Wuthuga), cormorants (Wanamalu) and bottlenose dolphins (Irrabuga). The two large temperate seagrasses Amphibolis antarctica (wire weed) and Posidonia australis (ribbon weed) tend to recover slowly and this prompted efforts for assistance.

wire weed seagrass adult plant and seedlings on the sand
Left: An adult wire weed plant with viviparous seedlings developing at the end of the branches. Image: Simone Strydom. Right: Wire weed seedlings washed up on the high tide. The grappling hook at the base of the seedlings enables them to attach to seagrass, seaweeds, and hessian, although many of the young plants wash up on beaches around Shark Bay. Image: Elizabeth Sinclair

'Snagging' wire weed

The selection of suitable plants and seedlings for restoration is guided by knowledge of their genomic diversity and adaptive traits, and different restoration methods have been applied to the plants at different growth stages (seeds, seedlings, and adults).

In August, the focus was on wire weed, as July to September is the peak dispersal time for the budding seedlings. The wire weed seedlings look like smaller versions of adult plants, but spend several weeks to months floating with the currents and tides, before eventually sinking to the seafloor and catching hold of something to grow on.

A wire weed seedling-retention technique involving ‘seagrass snaggers’ was trialled. These long hessian socks were developed by researchers after they trialled hessian bags in 2019. Seagrass snaggers can be filled with local beach sand. The hessian (and wire) will naturally break down over time. Ninety snaggers have been deployed at two locations, close to existing wire weed meadows. 

This method is simple, cheap, and easy, but timing is critical. The snaggers must be in place before the major release of seedlings begins. Ongoing work by Malgana Rangers on Sea Country means snaggers in coming seasons can be appropriately timed. The snaggers should last about 18 months: long enough for new seedlings to establish.

Malgana Rangers filling snaggers for seagrass restoration at Shark Bay
Left: Teamwork! Filling 'seagrass snaggers' with beach sand are: Nykita McNeair (Malgana ranger), Maryka Gray (lecturer, Geraldton TAFE), Sean NcNeair (Malgana Land and Sea Management Coordinator), Richard Cross (Malgana ranger), John Statton (UWA researcher) Alex Dodd (Malgana ranger) and Cody Oakley (assistant ranger). Right: John Statton with a boat load of filled snaggers. Images: Elizabeth Sinclair.
Malgana woman Bianca McNeair prepares snaggers for seagrass restoration at Shark Bay
Malgana Traditional Owner Bianca McNeair ties off 'seagrass snaggers': hessian bags used to retain seedlings for restoration. Image: Elizabeth Sinclair
People preparing to drop snaggers in the water for seagrass restoration at Shark Bay
Left: Malgana rangers Alex Dodd and Nick Pedrocchi prepare to deploy snaggers at a restoration site. Right: Over she goes! John Statton and Nick Pedrocchi deploy another snagger. Images: Gary Kendrick

Seeking signs of success

Measuring the success of restoration activities takes time (years rather than months) and requires multiple visits, particularly for the larger temperate species.

In October 2020, UWA researchers measured the return of ecosystem function at several restoration sites. These sites were established through traditional transplanting of adult plants. Some sites were planted in 2015 and 2018 (before the Hub project) and two new sites were established with Malgana Rangers in March 2020. The return of ecosystem function was determined by survival and shoot counts of transplants, and the presence of biodiversity (fish and invertebrates). 

There was expanded cover and increased shoot density at the older restoration sites. Fish diversity was highest in the oldest wire weed sites, and the survival of transplants was very high in the two Malgana Ranger sites, with lots of new wire weed shoots.

Temperate and tropical seagrasses recolonising the seafloor at Shark Bay
Left: Seaweed and algae growing on seagrass transplants. Right: This ribbon weed restoration site has been colonised by Halodule uninervis, a fast-growing tropical seagrass species eaten by dugongs (Wuthuga). The wire weed transplants are 2.5 years old. Images: Gary Kendrick
Seagrasses regrowing on the seafloor at Shark Bay
Left: Two months after deployment, the snaggers have embedded in the sandy bottoms, and collected some of 2020’s dispersing seedlings. Right: Eight months on, the wire weed (background) is growing new shoots while the ribbon weed (foreground) is looking healthy. It takes much longer for new ribbon weed shoots to emerge. Images: Gary Kendrick
Fish swimming among restored seagrasses at Shark Bay
Signs of returning ecosystem function. Butter fish explore a 2.5 year old ribbon weed restoration site. Image: Rachel Austin
A starfish amid restored Shark Bay
A starfish shelters at a 2.5 year old ribbon weed restoration site. Image: Rachel Austin

During the October visit to Denham, Professor Gary Kendrick of UWA formally presented the report A Snapshot of Marine Research in Shark Bay (Gathaagudu): Literature Review and Metadata Collation (1949-2020) to Malgana Elder Bobby Hoult, and Benny Bellottie. This comprehensive report summarises the past 70 years of marine research at Shark Bay.

A group of people from UWA and Malgana Rangers at a presentation of Shark Bay research
Prof. Gary Kendrick of UWA with Malgana Elder Bobby Hoult, and Alex Dodd, Richard Cross, Klaas Liezenga and Sean McNeair. Image: Rachel Austin

The Wirriya Jalyanu (seagrass) Festival was postponed due to unforeseen events that meant many members of the Malgana community would not have been able to attend. The Festival will now be held on 7/8 April 2021.

Related information

  • Working together to restore seagrasses at Shark Bay (story)
  • Seagrass (wirriya jalyanu): giving life to sea country of Shark Bay (Gathaagudu) (fact sheet 2021)
  • Restoration Showcase June 2020, "Assisting restoration of ecosystem engineers through seed-based and shoot-based programs in the Shark Bay World Heritage Site" (webinar presentation)
  • Kendrick GA, Nowicki RJ, Olsen YS, Strydom S, Fraser MW, Sinclair EA, Statton J, Hovey RK, Thomson JA, Burkholder DA, McMahon K, Kilminster K, Hetzel Y, Fourqurean JW, Heithaus MR, Orth RJ (2019). A systematic review of how multiple stressors from an extreme event drove ecosystem-wide loss of resilience in an iconic seagrass community. Frontiers in Marine Science 6: 455. 
  • Sinclair EA, Edgeloe JM, Anthony JM, Statton J, Breed MF, Kendrick GA (2020). Variation in reproductive effort, genetic diversity and mating systems across Posidonia australis seagrass meadows in Western Australia. AoB PLANTS 12: plaa038. 
  • Strydom S, Murray K, Wilson S, Huntley B, Rule M, Bessy C, Kendrick GA, Burkholder D, Fraser MW, Zdunic K (2020). Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area. Global Change Biology 26: 3525-3538.
  • Tan YM, Dalby O, Kendrick GA, Statton J, Sinclair EA, Fraser MW, Macreadie PI, Gillies C, Coleman R, Waycott M, van Dijk K-J, Vergés A, Ross JD, Campbell ML, Matheson FE, Jackson EL, Irving AD, Govers LL, Connolly RM, McLeod IM, Rasheed MA, Kirkman H, Flindt MR, Lange T, Miller AD, Sherman CDH (2020). Seagrass restoration is possible: Insights and lessons from Australia and New Zealand. Frontiers in Marine Science 7: 617.