Floating through the dreamscape of Victoria’s underwater forests

Floating through the dreamscape of Victoria’s underwater forests

February 18, 2023

By Miki Perkins

Marine life and habitat on reef near Point Nepean. Credit:Jason South

We’ve all had those dreams of flight, where you drift over a forest canopy and look down from your bird’s-eye view at the treetops below, waving in the wind.

Snorkelling above a seaweed-covered reef in Port Phillip Bay gives me a similar feeling. The bronze-coloured fronds of golden kelp billow and sway in the current. Seaweed in hues of pale pink and mauve stream over the edge of a rock crevasse, home to a timid group of blue-throated wrasse.

Marine Ranger Jack Dowson takes an audit of marine life and habitat on a reef near Point Nepean on Friday.Credit:Jason South

Above the water, the late-summer sky is cerulean blue and a container ship glides through the heads. Under the surface, the only sound is the gritty crunch of fish nibbling away at the reef. A group of four Parks Victoria rangers are snorkelling nearby, absorbed in assessing the health of this underwater forest.

Two decades ago, Victoria created its network of marine national parks and sanctuaries. Along the 2000 kilometre coastline, Parks Victoria manages 13 marine national parks and 11 sanctuaries – some 5 per cent of the state’s waters.

To mark this 20-year anniversary, Parks Victoria has undertaken a major research project with Deakin University to see if these parks and sanctuaries have fulfilled their purpose and protected Victoria’s diverse underwater habitats and species.

A Port Jackson shark on the floor of the reef at Point Nepean. Credit:Jason South

Researchers and marine rangers also checked the health of underwater environments to establish how south-eastern Australia’s unique marine animals and plants are faring in a warming climate.

“We brought a huge amount of data together to do a stocktake,” says Dr Michael Sams, the manager of the marine and coastal science program at Parks Victoria. “We wanted to know what’s living in our parks, and which habitats are well represented there.”

The news is largely positive. Deakin’s researchers found the state’s marine protected areas are comprehensive and a good representation of the varied ecosystems off the coast. The total number of fish and invertebrate species is higher inside marine protected areas, which shows their benefits in protecting biodiversity.

Rocky reef habitats, such as those visited by The Age this week at Port Phillip Heads Marine National Park, are well protected refuges and biodiversity hot spots for significant species, the survey found. As we floated along, the rangers spotted a dappled Port Jackson shark and a southern fiddler ray, its rounded shape prompting its common name, the banjo shark.

A horseshoe leatherjacket at Bunurong Marine National Park near Cape Paterson.Credit:Mark Norman, Julian Finn

Victoria’s marine parks are also home to fish such as the horseshoe leatherjacket, and invertebrates such as the greenlip abalone and southern rock lobster. The population numbers of these species have increased inside protected areas over the past two decades.

“When you look at species richness we tend to find it’s higher in marine protected areas and there’s a couple of key species, like the southern rock lobster, that are ecologically important,” says Sams. These rock lobsters are a “keystone predator”, meaning they hold together the complex web of relationships in an ecosystem. They eat invasive sea urchins, and are an indicator of a healthy reef.

Blacklip abalone are also declining across the state, although there are higher populations in protected areas. Another keystone species, they graze on dominant underwater plants on reefs, giving less-competitive species the space to colonise and flourish.

Dowson takes a photo as part of an audit of marine life and habitat.Credit:Jason South

One of the challenges in Victoria is public perception, says Sams: “Everyone thinks the Great Barrier Reef has all the diversity, but many Victorian species are not found anywhere. We have brilliantly colourful sponge gardens, full of invertebrates and reef fish.”

While marine parks are “no take” zones, meaning no fishing is allowed, they can have a spillover effect, replenishing marine animal populations beyond their boundaries to the benefit of areas of ocean where fishing is permitted.

Crayweed and a southern fiddler ray at Wilsons Promontory National Park.Credit:Tess Hoinville

The Deakin research also uncovered signs of ailing marine health, particularly spurred by climate change. While the kelp cover in the Port Phillip Heads National Park is in a “good to fair” condition, there are kelp declines across the state, particularly golden kelp and cray weed.

This is concerning because kelp creates large underwater forests for fish and invertebrates, and their decline means a loss of critical habitat. Like plants, they also take in sunlight and carbon dioxide to produce oxygen, and they play a role in keeping oceans oxygenated and clean.

In eastern Victoria this decline is linked to climate change, with the warming ocean increasing the range of the invasive long-spined urchin. This voracious grazer leaves large areas of reef permanently barren, but at one reef off East Gippsland, park rangers have had success in reducing urchin numbers with manual culling.

It’s 20 years since Victoria created its marine protected areas and new research has found they have fulfilled their purpose of protecting endemic species.Credit:Parks Victoria

Similarly, in the north of Port Phillip Bay, including the Jawbone Marine Sanctuary at Williamstown, the invasive purple urchin has exploded in number, creating vast area of urchin barrens – bare areas of rocky reef where seaweed should grow.

It’s a different story on the west cost, where kelp declines are believed to be linked to increased sea surface temperatures and wave energy, an effect of climate warming. The oceans off Victoria have warmed, on average, 1 degree since the 1970s.

Parks Victoria manages 13 marine national parks and 11 sanctuaries along the state’s 2000 kilometre coastline.Credit:Julian Finn/Museums Victoria/Parks Victoria

Victoria’s “soft sediment” ecosystems are not well represented in some marine parks, researchers found. While they might look like bare and lifeless stretches of sand, they are teeming with life within the sediment and when carpeted with seagrass they are important fish nurseries.

Some of Victoria’s marine national parks, such as Wilsons Promontory and Discovery Bay, are exposed to deeper, cooler water currents and upwellings that could help mitigate the effects of warming sea surface temperature under climate change. They could become important climate refuges in the future.

After our snorkelling trip, the marine rangers compared notes on the species they identified, and how numbers compared with the last survey of Port Phillip Heads National Park. They were buoyed to see the blacklip abalone were healthy and showed no signs of poaching, and there were no discarded fishing lines or damage caused by anchors.

Invertebrate richness at the Beware Reef Marine Sanctuary. Credit:Mark Norman

“I was pleasantly surprised post-summer,” said marine ranger Monique Bregman.

“I was expecting to see more damage and that wasn’t the case. There could have been a few more fish but we’d normally look for that in autumn or spring, when it’s cooler.”

If you see people fishing within marine protected areas you can call 13FISH (13 34 74) to report, or download the Vic Fishing app: www.vfa.vic.gov.au

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