National Ocean Account, Experimental Estimates

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Experimental estimates to measure changes in ocean ecosystems from 1988 to 2021.

Reference period
August 2022

Key statistics

  • In 2021 mangroves provided coastal protection services for 175 thousand people occupying 85.6 thousand dwellings.
  • In 2021 mangroves and seagrass combined provided up to 14.2 million tCO2e carbon sequestration services per year.
  • From 2020 to 2021, total mangroves increased 2.3% to 1.07 million ha.

Towards A National Ocean Account

Towards A National Ocean Account is a discussion article that highlights what was learnt through the development of the National Ocean Account with a view to the near future. The article is also a call for comments on the functionality and use of the accounts in this format.


In 2021, total mangroves increased 2.3% (23.5 thousand hectares).

Mangroves were:

  • closed forest (54%).
  • open forest (31.7%).
  • woodland (14.3%).

166 thousand hectares of mangroves showed increased canopy cover from 2020.

  • 34.5 thousand hectares of mangroves were established.
  • 130.4 thousand hectares increased in canopy cover.
  • 1.1 thousand hectares had a major increase in canopy cover.

60.2 thousand hectares of mangroves showed decreased canopy cover from 2020.

  • 6.4 thousand hectares of woodland were lost.
  • 4.6 thousand hectares of open and closed forest were lost.
  • 48.3 thousand hectares had a minor reduction in canopy cover.
  • 0.9 thousand hectares had a major reduction in canopy cover.

850.1 thousand hectares of mangroves showed no change in canopy cover.

Mangrove ecosystems were predominantly located in:

  • the Northern Territory (40.6%).
  • Queensland (34.9%).
  • Western Australia (21.3%).

The national increase was driven by increases in:

  • the Northern Territory (up 16.3 thousand hectares).
  • Queensland (up 3.7 thousand hectares).
  • Western Australia (up 3.5 thousand hectares).


As at 30 June 2021, the total extent of known seagrass meadows was between 2.56 million and 3.06 million hectares. Lower and Upper extent estimates are only available for the Gulf of Carpentaria, the Torres Strait, and the Great Barrier Reef World Heritage Area.

Approximately one third (32%) of seagrass is located outside state boundaries in other commonwealth waters, mainly in the Torres Strait.

Around 20% of seagrass is found in each of Western Australia, South Australia, and Queensland.

At the sediment compartment level, the largest contributors to seagrass extent were:

  • Cape York Peninsula (25% of total).
  • Cape York (14% of total).
  • Spencer Gulf (10% of total).
  • Gulf St Vincent (8% of total).
  • Lharidon (7% of total).

Estimates of seagrass density and persistence are available for the Gulf of Carpentaria, Torres Strait, and Great Barrier Reef. Over these areas:

  • The majority of seagrass was of variable density (69%).
  • Nationally 53% of seagrass was of unknown density.
  • The majority of seagrass was enduring (70%).
  • Nationally 62% of seagrass was of unknown persistence.

Carbon stock and Sequestration

As at 30 June 2021, 243 million tonnes of carbon were stored in mangrove ecosystems.

  • The Northern Territory has the largest amount of carbon stored in mangrove ecosystems.
  • This was driven by a combination of the Northern Territory having the greatest mangrove extent and storing a higher amount of carbon per hectare.

Between 289 and 341 million tonnes of carbon were stored in known seagrass meadows.

  • Seagrass outside state coastal water boundaries stored the most carbon (97 to 116 MtC). This was mainly around the Torres Strait with Cape York Peninsula (West) storing the most carbon of any sediment compartment (88 to 90 MtC).
  • Of the states, South Australia has the highest level of carbon stored in seagrass meadows (74 MtC). 66 MtC is in 2 sediment compartments: Spencer Gulf and Gulf of St Vincent.

Mangrove carbon sequestration services were 8.6 Mt CO2e per annum in 2021 (or the equivalent to emissions of 2.8 million cars), flat on 2016 (0.6% increase). 

  • A 1.7% decrease in service flows between 2011 and 2016 was primarily due to a loss in mangrove extent in Queensland and the Northern Territory. These services are split between vegetation (57%) and soil (43%) driven services.
  • The two largest contributors to carbon sequestration are the Bathurst & Melville Islands (North) (634 kt CO2e) and Van Dieman Gulf (746 kt CO2e) sediment compartments in the Northern Territory.

National carbon sequestration estimates for seagrass as at June 30 2021 range between 4.9 and 5.6 Mt CO2e (or the equivalent to emissions of 1.6 to 1.9 million cars).

  • Seagrass in South Australia provided the highest carbon sequestration services (1.75 Mt CO2e).
  • Cape York Peninsula (West) was the sediment compartment that provided the highest carbon sequestration service from seagrass (1.1 Mt CO2e).

Mangrove coastal protection

In 2021, 85.6 thousand dwellings received coastal protection services from Mangroves. The majority of dwellings (52 thousand) were in Queensland.

175 thousand people received coastal protection services from Mangroves. The majority of people (107 thousand) were in Queensland

18.8 thousand kilometres of Australia's coastline was offered coastal protection by mangroves. The states with the longest length of coastline protected were:

  • Western Australia (6.7 thousand km).
  • Northern Territory (5.7 thousand km).
  • Queensland (5.5 thousand km).

The replacement cost of mangroves offering coastal protection services is $218.7 billion dollars in seawall construction. The states with highest replacement costs were:

  • Western Australia had the highest replacement cost ($77.5 billion).
  • Northern Territory ($65.9 billion).
  • Queensland ($63.5 billion).

$2.2 billion in minimum annual services value and $8.7 billion in maximum annual services value as the economic replacement cost offered by mangroves.

Data downloads

Data files

Post-release changes

19/12/2022 – Closing Stock of Seagrass Persistence (Primary sediment compartments) updated to reflect persistence data

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