Global marine life on the move due to rising sea temperatures, study finds

A new study from the University of Southampton highlights the impact of climate change on marine environments as part of a relatively recent global phenomenon known as ‘tropicalisation’.

In the ocean, tropical species move from the equator toward the poles as sea temperatures increase. Meanwhile, temperate species are declining because temperatures are too hot, they face increased competition for habitat, and new predators are arriving on the scene, among other factors.

This massive movement of marine life, called tropicalization, is changing the ecological landscape of our oceans and leading to a cascade of consequences for ecosystems, biodiversity and potentially the global economy.

The study’s release coincides with the start of COP28, where global policymakers are coming together and committing to tackling the impact of global warming. Researchers say we need to better understand the consequences of tropicalization to predict its development, respond to its effects, and contribute to conservation efforts to protect the world’s biodiversity.

In recent years, climate change has altered the physical factors that affect species dispersal, such as ocean currents in areas separating tropical/subtropical and temperate regions. These boundary currents of warm water are warming faster than the global seawater average, facilitating the movement of species toward the poles and reinforcing the retraction of temperate species.

The first example of this process was identified in the Mediterranean Sea, now considered a “tropicalization hotspot” due to the increase in tropical species present. Since then, tropicalization has been documented globally in mid-latitudes.

Karolina Zarzyczny, a researcher at the University of Southampton and lead author of the paper, said: “Tropicalization has a multitude of ecological and evolutionary consequences on species, communities and entire ecosystems, with the potential to change patterns global diversity.

“Research over the past twenty years has primarily focused on ecological impacts, meaning that our understanding of its evolutionary consequences is limited. Given the close interaction between ecology and “Evolution, a comprehensive strategy that involves monitoring and action and integrates genetic and evolutionary research with the ecological changes we observe are essential to better understand the drivers and consequences of tropicalization.”

Gaps in our understanding

The study published in Trends in ecology and evolution is an in-depth review of the literature published over the past 20 years. This is the first step in making the scientific community aware of the gaps in our understanding of the problem.

“Although the abundance, distribution, and occurrence of species in tropical, subtropical, and temperate zones have been documented numerous times, there is a fundamental lack of understanding of the long-term evolutionary consequences once new species live together,” says Dr. Suzanne Williams. Scientific associate at the Natural History Museum and co-author of the article.

“Answering questions about how species evolve and interact with their environments involves using a variety of methods, including historical records and, of course, museum collections. Scientific data and museum specimens, both digitized and physical , constitute essential basic information for studying tropicalization.

Evolutionary consequences

Given the close interaction between ecology and evolution, altered interactions between species can lead to the evolution of new traits or behaviors. For example, in a recent study led by Dr. Phil Fenberg, associate professor at the University of Southampton, barnacles in temperate volcanoes have begun to “bend” to repel tropical predators that are expanding their ranges along the Baja California peninsula in Mexico.

Similarly, expanding tropical damselfishes and temperate reef fishes have been documented modifying their feeding and social behaviors to enable coexistence.

Other evolutionary consequences could involve the proliferation of more thermally resistant species or the loss of unique genetic diversity as temperate species recede. Such a reduction in genetic diversity could be problematic because it could affect the species’ ability to adapt to future stressors.

Socio-economic impacts

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

During her research, Karolina noted cases where salt marshes were replaced by ecosystems dominated by mangroves. Mangroves have greater carbon capture capabilities than the temperate salt marshes they replace, which could be good news for reducing CO.₂ levels in the atmosphere.

Additionally, the expansion of coral communities is expected to have a positive impact on the local economy due to increased dive tourism. That said, coral communities expanding due to tropicalization tend to be the same species and therefore do not offer the same variety of habitats that one would see in traditional coral reefs.

As part of this comprehensive study, the scientists involved call for urgent action in understudied regions (such as the temperate tropical regions of Africa and South America) to gain a comprehensive understanding of the driving factors and complex consequences that tropicalization can have, as well as how we can act. may begin to slow down its processes.

Conversation Efforts

Dr Phil Fenberg, associate professor at the University of Southampton and co-author of the paper, said: “One way to help mitigate the negative impacts of tropicalization is to create networks of marine protected areas in regions undergoing tropicalization. , we will be better positioned to eliminate other impacts beyond climate-induced effects, such as fishing pressure and habitat degradation.

“We can then give species a chance to acclimatize to tropicalization until we can take more substantial steps to slow global warming.”

Researchers need to conduct more monitoring of ecosystems undergoing tropicalization to better understand the drivers and dynamics of tropicalization. To do this, researchers need an abundance of data from a variety of sources, such as fisheries catch records, citizen science projects and modern biodiversity surveys. Future studies could also use advanced monitoring technology to detect DNA from marine organisms in the environment (called eDNA) in regions undergoing tropicalization.

“The ecological and evolutionary consequences of tropicalization” is published in the Trends in ecology and evolution.