Study highlights the impact of climate change on marine ecosystems

• New study investigates a phenomenon known as tropicalisation, where warming oceans are causing changes to marine life ecosystems.
• Scientists are calling for more research to be done to gain a clearer understanding of how this process is impacting fragile marine environments.
• An extensive review on research conducted to date shows that the phenomenon is happening on a global scale, is on the rise and there is limited understanding on the evolutionary extent of the issue.

A new study shines a light on the impact modern climate change is having on marine environments in a relatively recent global phenomenon known as ‘tropicalisation’. The release of this study coincides with the start of COP28, where global policymakers convene and make pledges to tackle the impact of global warming.

The term tropicalisation encompasses the shift of tropical marine species poleward into temperate regions as these areas rise in temperature. This, in turn, leads to the retraction of species native to temperate regions, as it gets too warm or they face increased competition for habitat or fend off new predators. Consequently, tropicalisation is changing the ecological landscape of our oceans globally.  

This study reveals that these changes could have significant ecological, evolutionary and socioeconomic consequences and calls for haste in understanding the consequences of tropicalisation and predicting its development. Authors of the paper put forward that mitigating these consequences is key to safeguarding ocean biodiversity and the services it provides.

Karolina Zarzyczny, University of Southampton/Natural History Museum, was lead author of the paper, under the mentorship of Dr Phil Fenberg, University of Southampton/Natural History Museum and co-supervised by Dr Suzanne Williams, Principal Researcher at the Natural History Museum and Dr Marc Rius, Director of the Centre for Advanced Studies of Blanes (CEAB).

Karolina Zarzyczny said, ‘Research conducted over the past twenty years has mostly focused on ecological impacts, meaning our understanding of its evolutionary consequences is limited.’

‘Given how closely ecology and evolution interact, a comprehensive strategy that involves genetic and evolutionary research with the ecological changes we’re seeing is essential to better understand the drivers and consequences of tropicalisation.’

This extensive review of the literature published over the past 20 years was the first step in impressing upon the scientific community the gaps in our understanding of the problem.  

‘Although the abundance, distribution and presence of species across tropical, subtropical and temperate zones has been documented many times, there is a fundamental lack of understanding of the long-term evolutionary consequences once new species live together’, comments Suzanne, Natural History Museum.

‘Answering questions about how species evolve and interact with their environment involves employing a variety of methods, including historical records and, of course, museum collections. The scientific data and specimens from museums, both digitised and physical, are key baseline information for studying tropicalisation.’

Documenting tropicalisation is one step, but Karolina and scientists from the Natural History Museum, the University of Southampton, and CEAB are calling for greater attention to be paid to the evolutionary consequences of these patterns.

Given how closely ecology and evolution interact, altered species interactions may lead to evolution of new traits or behaviours. For example, in a study led by Phil and co-authored by Karolina, temperate volcano barnacles have begun to “bend” to fend off new tropical predators along the Baja California peninsula in Mexico.

Other evolutionary consequences might involve the loss of unique genetic diversity as temperate species recede. Such reduction in genetic diversity could be problematic as it may affect the species ability to adapt to future stressors.

The phenomenon is not just an ecological concern; it also carries substantial socio-economic implications, not all of which are negative.

During her research, Karolina noted instances where saltmarshes were being replaced by mangrove-dominated ecosystems. Mangroves have greater carbon capture capabilities than the temperate salt marshes they are replacing - a good news story for reducing CO2 levels in the atmosphere.

Furthermore, the expansion of coral communities is expected to have a positive impact on the local economy due to the increase in dive-based tourism.

Within this extensive study, scientists involved are calling for urgent action in addressing poorly studied regions (such as tropical-temperate regions of Africa and South America) to gain a holistic understanding of the drivers and complex consequences tropicalisation can have, as well as how we can begin to slow down its processes.

Dr. Phil B. Fenberg, Associate Professor at the University of Southampton, said: ‘One way to help mitigate the negative impacts of tropicalisation is to create networks of marine protected areas in regions undergoing tropicalisation. In these protected areas, we will be better positioned to remove the other impacts outside of climate-induced effects, like fishing pressure and habitat degradation.

‘We can then give species a chance to acclimatise to tropicalisation until we can take more substantial action in slowing global warming.’

A key point of the paper is that researchers need to conduct more monitoring of ecosystems undergoing tropicalisation to better understand the drivers and dynamics of tropicalisation.

To do this, researchers need data from various sources, such as fishery catch records, citizen science projects and modern biodiversity surveys. Future studies should also use cutting-edge monitoring technology to detect the DNA of marine organisms within the environment (called eDNA) in regions undergoing tropicalisation. 

The findings of the review have been published in the Trends in Ecology and Evolution journal and can be accessed here: https://doi.org/10.1016/j.tree.2023.10.006

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