PARK WATCH Article March 2025 |

Kade Mills, ReefWatch Coordinator, says when it comes to invasive seaweeds, if you can’t beat ‘em, or eat ‘em, you can always compost ‘em!

Picture this: you’re floating in the waters of Port Phillip Bay/Nerm, marvelling at the vibrant marine life in an underwater forest of seaweed. Beautiful, isn’t it? But often, that seaweed forest is dominated by an uninvited guest – Undaria pinnatifida (Undaria).

This fast-growing, highly reproductive invasive algae has spread throughout the bay since 1996, displacing native seaweed in many locations. But here’s the good news: divers and community volunteers are fighting back through hands-on conservation and even a little culinary creativity!

Managing unwanted guests

Port Phillip Bay is home to over 160 invasive marine species. Among them, Undaria is one of a few listed on the International Union for Conservation of Nature (IUCN) top 100 worst invasive alien species. First detected at Point Wilson in 1996, it has since spread to Apollo Bay, Portland and Port Welshpool, attaching itself to reefs, pylons, and boat hulls.

Completely eradicating Undaria isn’t realistic. Instead, management efforts focus on preventing its spread to new areas and reducing its numbers. While boating regulations help limit its spread, many recreational divers and snorkellers remain unaware of the problem lurking beneath the surface. With Undaria poised to invade new coastal areas, awareness and action are more important than ever.

Why is Undaria such a bad guest?

The secret to Undaria’s success lies in its adaptability. It grows rapidly, reproduces prolifically, and can pause its development during unfavourable conditions. Reaching up to three metres in height, a single plant can release up to 700 million microscopic spores (marine seeds) over its lifetime. To make matters more challenging, these microscopic ‘seeds’ can survive for up to 2.5 years, making eradication particularly difficult. With such resilience, Undaria has quickly outcompeted native seaweed, reshaping underwater ecosystems.

Underwater Weeding Project

To bring Undaria’s spread to light, the Underwater Weeding Project was launched in 2022. The initiative empowers divers to take action by manually removing the invasive seaweed.

But it goes beyond conservation – the project explores the growing potential of seaweed as a sustainable food source.

By incorporating seaweed into diets, we could reduce reliance on traditional crops. Instead of treating Undaria as waste, it has been composted, cooked, and repurposed, turning an ecological problem into an opportunity.

The results? A sea of change!

  • Environmental impact: Volunteers removed 11,767 Undaria plants from 12 sites across the bay. That’s a lot of underwater gardening!
  • Community engagement: 422 participants took part, educating 356 curious beachgoers about why tackling this marine pest matters.
  • Beyond just weeding: While at it, volunteers also removed Northern Pacific Seastars (another uninvited guest) and marine debris.

How did we make a splash?

  • Training divers to weed like pros: Participants learned to safely remove Undaria without damaging native seaweed.
  • Perfectly timed weeding missions: Events were scheduled during Undaria’s peak growth season in Winter, keeping divers active during the off-season.
  • Sustainable solutions: Removed seaweed was composted, cooked, and explored for alternative uses instead of being sent to landfill.

What’s next?

  • Undaria removal is now a dive club tradition: Many groups have added Undaria hunts to their annual dive calendars.
  • Tracking the impact: A dedicated portal on the Atlas of Living Australia allows for ongoing data collection and collaboration.
  • Bigger and bolder conservation efforts: Can public involvement help control other marine pests? Absolutely! More hands mean fewer invaders.
  • Long-term studies needed: Researchers and community groups need to monitor native seaweed recovery for 5–10 years post-Undaria removal.
  • Scaling up kelp restoration: By combining invasive species removal with restoration efforts, we can help native seaweed reclaim its underwater kingdom.

The Underwater Weeding Project proves that conservation can be hands-on, engaging, and even delicious. Through community action, education, and creative solutions, we’re fighting back against invasive species and protecting Port Phillip Bay for future generations.

So whether by weeding, composting, or even eating the invaders – every effort counts!

Note: All work was conducted under a permit, which is available from the Victorian Fisheries Authority. If you’re interested in tackling some weeding yourself, contact us for guidance on obtaining a permit.

Read the full report on the Underwater Weeding Project