Seafood industry threatened by ocean acidification and heating

Abalone Narooma owner Stephen Bunney has been a commercial abalone fisherman for 33 years and has witnessed a large tropicalisation of the marine environment off the south coast during this time.

He dives almost daily in the waters off Narooma and said he had watched as brown kelps such as crayweeds and Ecklonia radiata had withdrawn south.

"I've seen the complete loss of reef systems in places like Montague Island," Mr Bunney said.

Montague Island, off the coast of Narooma, used to have a kelp forest the size of a football field which was a a significant abalone growth area.

"It has transitioned from abalone habitat to sea-urchin barren," he said.

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"Bull kelp has been withdrawing south for the last 30 years. When I started, you would find bull kelp at Mystery Bay, now you'd have to go as far south as Merimbula for any chance of finding it."

He has witnessed changes like this all along the south coast - high-value kelp habitats with high abundance and high biodiversity becoming critically endangered and diminishing.

He said the ocean adjacent to the NSW far south coast was warming four times faster than anywhere else on the NSW coast.

The NSW south coast forms part of the 8000 kilometre Great Southern Reef stretching from southern Queensland to Kalbarri, in Western Australia.

Mr Bunney said the whole reef system was interconnected, forming a bridge for species to migrate and helping keep marine ecosystems healthy.

"These systems rely on each other," he said. "When you lose them, it diminishes the links between the marine kelp habitats which has a widespread impact.

"You see lots about the bleaching of the Great Barrier Reef but the Great Southern Reef is just as important, and it's under threat as well."

Nature Coast Marine Group president Dr Jane Elek said higher CO2 levels in the atmosphere increased the acidity of the ocean.

"Our ocean on planet earth has been buffering the effects of changing climate," Dr Elek said.

"It has absorbed 90 per cent of the heat and 30 per cent of the CO2 we are belching into the atmosphere."

When the CO2 dissolves in the ocean it forms carbonic acid; Dr Elek said human activity had caused ocean acidity to increase 30 per cent in the last 200 years.

She said the effect was concentrated towards the surface of the water, where lots of sea life lived.

This increased acidity hinders shellfish from extracting the vital calcium they need from seawater to construct and maintain their shells.

Dr Elek said as acidity increased, shells would start to dissolve.

"This will especially affect tiny zooplankton such as krill and larval shellfish that are important food for many larger marine animals, including our favourite fish," she said.

The Australian seafood industry is currently worth more than $2 billion, of which one third is shellfish. A 2016 study by the Conversation found the fishing industry contributed $436 million in revenue annually to the NSW economy.

Dr Elek fears this is all at risk by the effects of rising ocean acidity and temperature.

She said increased acidity had the potential to cause serious long-term disruptions to the industry, and could lead to the prevalence of more waterborne diseases, or the distortion or death of juvenile abalone or oysters.

Mr Bunney has spent his life working in the industry and loves being underwater and witnessing the beauty and diversity of marine ecosystems.

"As someone who is diving and witnessing underwater ecosystems often, you have this duty of care to do something about it if you are seeing change," Mr Bunney said.