Calculating the global economic costs of aquatic invasive alien species – Fellows’ seminar by Tatenda Dalu

13 February 2023

“I study animals but not the large, charismatic ones. My passion is aquatic species – the cool crabs, tadpoles, plankton, etc. My work is aimed at understanding the interactions in aquatic ecosystems including the terrestrial environment and social interactions,” said Tatenda Dalu of the School of Biology and Environmental Sciences at the University of Mpumalanga. “My interest in the field is about maintaining the environment in its natural state. Alien invasion changes the natural environment. But, of course, different people and interests view it differently. We need balance in actions and words.”

STIAS Iso Lomso Fellow Tatenda Dalu during his seminar on 9 February 2023

Biological invasion is an increasing problem and will continue to increase – by an estimated 36% by 2050 across all taxonomic groups, regions and habitat types. Dalu pointed out that there are well-described ecological impacts – aliens are the second-most common extinction driver. Species loss varies by region and animal, and most management attempts are insufficient to curtail invasion rates.

“There’s an urgent need to prevent invasion but how do you motivate research? We need buy in from policy makers, governments and other stakeholders.”

And part of that involves pointing out the economic costs.  “Monetary value is usually needed to incentivise political action.”

“Much research effort has been invested in understanding the ecological impacts of invasive alien species (IAS) across ecosystems and taxonomic groups, but empirical studies about economic effects lack synthesis,” he said.

Dalu and his colleagues are therefore developing a comprehensive global database to determine patterns and trends in economic costs of aquatic IAS by examining the distribution of these costs across taxa, geographic regions and cost types; the temporal dynamics of global costs; and, highlighting the knowledge gaps, especially compared to terrestrial IAS.

The work started with a systematic review of published research including nearly 2000 articles. Immediately apparent was a bias towards a few species and regions with massive data gaps. “Many countries and known aquatic alien species had no reported costs, especially in Africa and Asia.” From Africa most of the work comes from South Africa and Zimbabwe and from countries in West Africa – there is not much else.

Counting dollars

But even with obvious gaps, the figures are striking.

“Based on the costs recorded from the literature, the global cost of aquatic IAS conservatively summed to US$ 345 billion, with the majority attributed to invertebrates (62%), followed by vertebrates (28%), and plants (6%). The largest costs were reported in North America (48%) and Asia (13%) and were principally a result of resource damage (74%); only 6% of recorded costs were from management. The magnitude and number of reported costs were highest in the USA and for semi-aquatic taxa.”

“Aquatic IAS costs have increased in recent decades by several orders of magnitude, reaching at least US$ 23 billion in 2020,” continued Dalu. “Costs are likely to be considerably underrepresented compared to terrestrial IAS; only 5% of reported costs were from aquatic species, despite 26% of known invaders being aquatic. Additionally, only 1% of aquatic invasion costs were from marine species.”

“Costs of aquatic IAS are thus substantial, but underreported. They have increased over time and are expected to continue rising with future invasions,” he added.

Microscopic but deadly

Information on microscopic aquatic taxa specifically are a missing link.

Looking at plankton, the researchers found that from 1960 to 2021 the cumulative global cost of plankton invasions was US$ 5.8 billion for permanent plankton (holoplankton) of which viruses encompassed nearly 93%.  More costs were related to zooplankton (US$ 297 million) than to the other groups summed including myco-(US$ 73 million), phyto-(43 million), and bacterioplankton (US$ 0.7 million).

“Strikingly, harmful, and potentially toxic cyanobacteria and dinoflagellates are completely absent from the database,” said Dalu. “Also, assessments of the costs of larval meroplanktonic stages of littoral and benthic invasive invertebrates are lacking whereas the cumulative global cost of the adults stages is high – up to US$ 98 billion and increasing. Considering the challenges and perspectives of increasing but unnoticed or neglected impacts by plankton invasions, assessment of their ecological and economic impacts should be of high priority.”

Overall the sectors impacted by all of this include agriculture, fishing, health, public welfare, environment, and community stakeholders. “Obviously in terms of aquatic species the biggest impact is on fisheries as this affects the quality of meat coming from aquaculture.”

Based on these figures, Dalu and his colleagues highlight the need for more research to fill the knowledge gaps especially for aquatic taxa, the need for increased and improved cost reporting by managers, practitioners and researchers; and, an urgent priority for increased management spending to prevent and limit current and future aquatic IAS damage.

He pointed out that delays in managing the problem add substantially to the costs. “Globally few governments have allocated funds for pre-invasion avoidance and management, with most channelling funds post-invasion which, in most cases, will be a little bit too late – it’s estimated that quicker action could have saved US$ 1.2 trillion.”

But it’s also important to do comprehensive risk assessment to understand all the impacts of the different biological control agents used to manage invasions. “There have been different results in terms of management – with many more examples from terrestrial species. There are successes but also setbacks. We need to ensure that new biological control agents don’t destroy the indigenous. The Working for Water project in South Africa has had some success in clearing alien species in water sources. Scientists are now quantifying the effect of the different methods. It’s all about balancing economic and management costs.”

“Some invasive species also do have economic benefits but the impact differs,” he added. “We need to balance the pros and cons of management.”

The discussion highlighted the need for clear definitions of invasive, different narratives and more democratic decision making around environmental issues, and to engage more stakeholders to fully understand who pays and who benefits both from environmental change and the management measures.

Dalu explained that invasive is usually defined as species introduced by humans to a new area, causing damage and characterised by fast growth and the ability to outcompete indigenous species.

“But,” he said, “we need more fundamental research to know where the baseline starts – going right back to know which species moved from where and how they are shared across different areas.”

“Our aim is to highlight global biases and gaps in research and where the money needs to go,” he said.


Michelle Galloway: Part-time media officer at STIAS
Photograph: Noloyiso Mtembu


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