Assessing the effectiveness of removals of Undaria pinnatifida at Point Cooke Marine Sanctuary

Point Cooke Marine Sanctuary, on the north western shores of Port Phillip Bay, supports a considerable population of the Japanese kelp or Wakame, Undaria pinnatifida, which has been identified as being one of the highest... [ view full abstract ]

Point Cooke Marine Sanctuary, on the north western shores of Port Phillip Bay, supports a considerable population of the Japanese kelp or Wakame, Undaria pinnatifida, which has been identified as being one of the highest priority invasive marine pest species to have reached the Australian marine environment. This project is aimed at investigating and quantifying the densities and size frequency distribution of the population within the marine sanctuary (with the use of quadrats and transect line surveys), and aims to determine the effectiveness of removals of this macroalgae. Undaria is a seasonal species, and exhibits rapid growth from winter through to spring (July to September), but then dies back rapidly during the summer months (December to February), to the extent that the sporophyte (blade) of the plant is either dilapidated or is no longer present (Campbell et al. 1999).
Investigations conducted between September 2014 and April 2015 (involving the removal of 323 plants) have revealed a paucity of mature adult plants that had died back and had started regenerating, suggesting that adult plants may suffer high mortality after the shedding of gametes, and may not regenerate as actively as once thought. The population appears to be composed largely of immature individuals of minimal size (average 156 mm in total length and less than nine grams total wet weight), with 56% of the surveyed plants lacking sporophylls (the main reproductive organ). It therefore seems that at this particular location, the key survival strategy of this plant is to procreate rather than regenerate, with recruitment of juveniles at densities of less than one plant per square metre the norm, though as many as four or five plants are often found clustered together.

This project is ongoing and is due for completion in June 2016, and has been funded by grant monies from the “Communities for Nature” program established by the Victorian State Government, and is being run in association with Parks Victoria, Marine Care Point Cooke (a friends group composed of volunteers) and Melbourne Polytechnic.