/ 11 August 2023

Our blue seas are gradually going green

Lighthouse At The South Beach In Front Of Blue Sky
Over the past 20 years, the colour of our oceans has gradually been changing from blue to green. (Photo by: Dukas/Universal Images Group via Getty Images)

Over the past 20 years, the colour of our oceans has gradually been changing from blue to green and it’s being attributed to human-induced climate change. These changes can have knock-on effects on the health of the ocean and the resources we so heavily depend on, such as fishing — and oxygen. 

South Africa has a coastline of around 3 000km and it’s surrounded by three oceans: the South Atlantic, the Indian and the Southern. The WWF estimates that about 12 000 marine species live in these waters but, as temperatures change, they are migrating to different habitats which is disrupting the intricate ecosystem in the ocean. The creatures are thus challenged with finding food, forming habitats, reproducing and surviving.

The study, published in Nature journal in July, found that as oceans warm up, microorganisms are shifting course, and that’s changing the colour of the oceans. 

Matthew Germishuizen, PhD Candidate from the Mammal Research Institute Whale Unit in the Department of Zoology and Entomology at the University of Pretoria explained the science behind the phenomenon. 

The ocean contains millions of single-celled algae called phytoplankton which use the process of photosynthesis to convert sunlight, water and carbon dioxide into energy. 

The action is driven by a green substance in the algae called chlorophyll and it’s only detectable by satellites. The productivity of this algae is what causes the greening and it’s linked to both climate change and the ocean’s circulation — a climate regulatory pattern that stores and transports heat, carbon, nutrients and freshwater all around the world. 

South Africa has diverse and sensitive ecosystems, especially in the tropical habitats in parts of northern Kwa-Zulu Natal where coral reefs are abundant, and Germishuizen said rapid greening can severely impact these sensitive habitats.

However, he cautions that 20 years of data might not be sufficient to distinguish natural variability from climate change effects, and longer time periods are needed to better understand ocean colour changes in response to climate change.

Fishing industry 

South Africa’s fishing sector is also likely to feel the effects of climate change. It contributes around R6 billion a year to South Africa’s GDP, and directly employs about 27 000 people in the commercial sector, according to the Department of Agriculture, Forestry and Fisheries. The industry, and the people whose livelihoods depend on it, are likely to suffer great losses if the ocean’s ecosystems continue to change. 

Charlotte Scott, a PhD researcher working on locally-led food systems and climate justice, said that it’s important that we understand the role of climate change on small-scale fishers, especially. 

“As our oceans get warmer, and our weather gets more extreme, coastal and fishing communities are likely to be impacted in multiple ways, compounding the existing challenges and inequalities they face. 

“We’re likely to see more intense and more frequent extreme weather events, meaning that fishers have fewer days to fish and might have to go fishing in worse conditions, putting them at a greater risk to make a living.”  

The climate crisis could worsen as temperatures increase in Africa and around the world, we’re likely to feel its impact more directly, and we should pay more attention to what’s happening around us. 

As Germishuizen said: “The ocean is critical to every single human on the planet. Changes to the ocean will affect everything from trade, to water availability. The fear is that we will only realise how important the ocean is once it is too late. So, the key message is to change our ways faster and sooner rather than watch and wait.”

No matter which angle you look at it from, the message is clear — the climate crisis needs more attention. Our deep (blue-green) seas are a beautiful resource and we need to do more for them and all who live in them.