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21 April 2021 9 min read

Over 70 per cent of Earth’s surface is ocean. The ocean drives our weather, and influences both land and marine ecosystems. It is highly complex and of huge value to communities around the globe. Decisions that support a sustainable future for the ocean must account for this complexity and mitigate potential impacts at local, national and international scales. To help decision-makers navigate these complex waters, the United Nations has launched the Second World Ocean Assessment (WOA II).

Assessing the world’s ocean

The benefits humans gain from the ocean include climate regulation, coastal protection, food, employment, recreation and cultural well-being. However, these benefits can only be maintained if we are able to successfully protect the world’s ocean from the increasing pressures it faces.

In 2016, the United Nations General Assembly welcomed the First World Ocean Assessment (WOA I). This global integrated marine assessment (the first of its kind) aimed to cover all environmental, social and economic aspects related to the ocean. Its purpose was to provide a baseline on the state of the ocean, including human uses, and the relationships between humans and the ocean. It aimed to help decision makers in all sectors better understand the global and regional state of the ocean.

Our understanding of the ocean, the pressures impacting the ocean and the processes used to manage it is constantly improving. Following the release of the first assessment, a second group of experts was brought together to deliver an updated assessment of the world’s ocean – WOA II – that would reflect this improved understanding.

The front cover of the Second World Ocean Assessment, showing the title, volume and a fisheye image of divers swimming over a coral reef.
The United Nation’s Second World Ocean Assessment provides up-to-date information about the global and regional state of the ocean, covering all environmental, social and economic aspects. Cover photo: Yung-Sen Wu, United Nations World Oceans Day Photo Competition. Copyright © United Nations, 2021. All rights reserved. Printed at the United Nations, New York.

One of that select group of 19 hand-picked experts from around the world was CSIRO’s Dr Karen Evans. As Australia’s sole representative on the group coordinating the development and delivery of WOA II, Dr Evans took a key role in ensuring the southern hemisphere was represented throughout the process.

“Being part of the group of experts nominated by their governments to lead the development of this second World Ocean Assessment has been a wonderful opportunity,” said Dr Evans.

“Having a CSIRO representative at the table gave credibility to the process and allowed us to showcase some of the world-leading science that’s happening across Australia. It also meant that the southern hemisphere component of the ocean, and in particular the southern Pacific Ocean and Indian Ocean were not underrepresented, as has previously sometimes been the case.”

The assessment covers the following key areas:

  • Relevant drivers of change in the ocean
  • Trends in the current state of the main components of the marine environment, including groups of species, types of habitats and human society, including maritime industries
  • Pressures and their impacts on the ocean, including relevant socioeconomic components
  • Management measures adopted in response to those pressures and impacts.

Along with Dr Evans, several CSIRO researchers were involved in the preparation of the assessment. Here we discuss the three chapters that were led by CSIRO researchers. To read the full assessment head to

Marine reptiles – conservation status and threats

WOA II provides an updated assessment at a global scale of the conservation status and main threats to marine turtles, snakes and iguanas. As lead author, CSIRO’s Dr Qamar Schuyler explains, it identifies regional trends and highlights changes that have occurred since WOA I.

“Some marine turtle populations have experienced positive growth rates since WOA I, but overall, trends are still decreasing and many threats remain for these animals,” said Dr Schuyler.

“For example, the global status of loggerhead turtles has improved from endangered to vulnerable, but Kemp’s ridley turtles went from endangered to critically endangered in the period between WOA I and WOA II.”

Overall, marine turtle populations have been decreasing since WOA I.

The authors found that the conservation status of most sea snake and marine iguana populations remained at similar levels to those from WOA I. However, large data gaps made this difficult to assess.

The threats to marine reptiles also remained similar to those documented in WOA I.

“The most significant threat to marine reptiles is bycatch,” said Dr Schuyler.

“Other key threats include unregulated harvesting, marine pollution, habitat loss, coastal development, disease and climate change.”

Cumulative effects – increasing pressure from multiple sources

Our complex marine ecosystems are under growing pressure from human-derived climate change, extraction of resources, pollution (from land and marine sources) and invasive species. These pressures are interacting with each other and with natural processes to cause biodiversity loss, habitat damage and fragmentation, and disease. Taken together, these pressures have cumulative effects on the marine environment.

There is a need to better measure and manage the cumulative effects of human activities and natural events to improve the outlook for the marine environment. We need to identify solutions to prevent and/or mitigate these effects and their impacts. As Dr Evans (who was lead author for this chapter) explains, WOA II provides a foundation for addressing these needs by providing an overview of the various approaches used to assess cumulative effects and their outcomes.

“We found many different approaches for assessing cumulative effects,” said Dr Evans.

“But by and large they involved three main steps: 1) gather information about the activities that may be affecting the ecosystems, 2) determine how the different parts of the ecosystem are responding, and 3) identify measures managers could take in response.”

This graphic shows just some of the human activities and natural events impacting our marine environment and that need to be considered when making management decisions. Credit: Beth Fulton, CSIRO.

WOA II notes that the use of cumulative effects assessments (CEAs) has increased over the past two decades. However, they aren’t widely used outside Europe and North America. This suggests a need to improve knowledge and capacity gaps, particularly in developing nations.

“To support the wider use of CEAs around the globe we need to develop easily implementable approaches that can be used despite a lack of data, and that produce outputs that are easy to understand and incorporate into decision-making processes,” said Dr Evans.

One marine environment where cumulative effects have been clearly identified and measured is the Great Barrier Reef Marine Park. The development of policy and science to deal with these impacts is showcased within WOA II.

“We selected the Great Barrier Reef as a case study as it is a world-leading example of the potential for cumulative effects assessments to effectively guide management decisions,” said Dr Evans.

Rigorous science has clearly demonstrated the impact of cumulative effects on the Great Barrier Reef. The CEA approach detailed in WOA II has been used to develop a framework that is enabling managers to explore a range of hypothetical interventions, consequences, and trade-offs. The framework is world-leading because it moves beyond looking at cumulative effects in a linear sense. It takes into account the fact that pressures don’t always add one on top of the other, instead they might interact to reduce or multiply impacts.

“The science that’s happening on the Great Barrier Reef is at the forefront of research around cumulative effects,” said Dr Evans.

“It’s a really rare case to have a strong marine park management structure, through the Great Barrier Reef Marine Park Authority, running a formal evaluation process that culminates in a set of guidelines that are written into all planning and approval processes at the regional level. It was wonderful to be able to showcase this example on the world stage.”

Developments in approaches for managing the marine environment

Over the past decade, the way we manage ocean resources and sustainability has undergone considerable change. In recognition of this change and the importance of management in the successful conservation and sustainable use of our oceans, WOA II provides for the first time an overview of different approaches and explores some examples of good practice from around the world. As the lead author, CSIRO’s Dr Piers Dunstan, explains the ecosystem approach is a key focus of the chapter.

“One of the most significant developments over the past decade has been the global consensus that the management of resources needs to take on an ecosystem approach,” said Dr Dunstan.

“This is an integrated approach, incorporating the environmental, social and economic management of human interactions with the ocean at scales ranging from local to international. Importantly, the ecosystem approach draws in perspectives from all relevant areas of society, including governments, industries, communities and traditional owners.”

WOA II also highlights some of the hurdles that need to be overcome if we are to maximise the benefits derived from using the ecosystem approach. Particularly in developing countries where there is a need to improve understanding of management approaches and the tools to implement them.

In support of this, WOA II provides an overview of current decision-making processes and management tools. Management tools are specific actions that can be taken to regulate and modify human activity in a particular system. Examples include the introduction of Marine Protected Areas or World Heritage Sites, catch controls and pollution regulations. Decision-making processes provide a framework to help identify the most appropriate tools for achieving specific outcomes. Examples include marine spatial planning, integrated coastal zone management, and systematic conservation planning.

Introducing Marine Protected Areas or World Heritage Sites, such as has been established for the Great Barrier Reef, is one example of a management tool that can be used to regulate human activity in a marine system. Credit: Matt Curnock, CSIRO.

The chapter demonstrates the breadth of options available for the effective management of our ocean environment. But, as Dr Dunstan explains, there is more that needs to be done, particularly if we are to meet the UN’s Sustainable Development Goals for the ocean.

“Managing our marine environment is a no simple task,” said Dr Dunstan.

“We’ve come a long way in the past decade, but significant challenges remain. If we hope to achieve the ocean-related Sustainable Development Goals we need to implement the ecosystem approach and integrate management across sectors. This will allow government, industry and communities to share the benefits and trade-offs occurring across the marine environment, while also valuing different perspectives across society.”

The above is just a drop in the ocean when it comes to the amount of information contained in the WOA II. If you’d like to dive deeper head to

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