Seaweed blooms are expanding – and transforming the Global Ocean. – oceanbites

Qi, L., Wang, M., Barnes, B.B. et al. Global floating algae blooms are expanding. Nat Commun 17, 612 (2026). https://doi.org/10.1038/s41467-025-66822-5

Have you ever seen an image of a seaside fully coated in a reddish seaweed washed ashore? Or maybe you’ve skilled this your self alongside the tropical Atlantic coast. What must be a stress-free, refreshing seaside day can rapidly flip disagreeable.

Scientists have identified for years that these macroalgal blooms – a class of algae together with seaweed – have been growing in some areas, however till not too long ago, there was no clear international image. That modified with a new examine revealed in Nature, offering the first large-scale evaluation of floating algae throughout the world’s oceans.

In this examine, scientists used artificial intelligence to take a look at over 1.2 million satellite tv for pc photos taken from 2003-2022 to trace floating algae throughout the world’s oceans. The findings have been putting – seaweed blooms in each the tropical Atlantic and western Pacific expanded at an unprecedented fee of 13.4% per 12 months since 2003. This fast increase suggests a main shift in the international ocean. What was as soon as thought-about a regional concern is now clearly a widespread, international phenomenon.

The time period floating algae refers to each microalgae and macroalgae. Most ocean water is full of tiny organisms invisible to the bare eye known as phytoplankton or microalgae. Although particular person phytoplankton are minuscule, collectively, they supply over half of the world’s consumable oxygen by way of photosynthesis. This sort of microscopic algae is detectable by way of satellite tv for pc imagery and laboratory techniques, and it has been studied extensively. We know a lot about its distribution and trends over time as our oceans have modified.

But there’s one other sort of algae that has not been studied as a lot – macroalgae like seaweed. Although it’s seen to the human eye, its international patterns haven’t been studied as extensively. Just like microalgae, macroalgae are important in supporting marine life and sustaining healthy ecosystems. However, extreme quantities of macroalgae in coastal waters and on seashores might be dangerous to the surroundings, human beings, and economies. Several native experiences have demonstrated will increase in macroalgae over the previous decade, however what does the international image appear to be?

By analyzing international satellite tv for pc photos, the scientists have been capable of establish international trends in the two sorts of floating algae. Floating algae now occupy an monumental 43.8 million sq. kilometers, which is roughly 12% of the international ocean’s floor space (Figure 1). They are concentrated in the tropical Atlantic and western Pacific ocean areas.

Splitting the information up into 10-year intervals clearly revealed that there’s more floating algae in the previous 10 years relative to the first 10 years (Figure 2). While each macroalgae and microalgae are growing, the most fast increase has occurred in macroalgae. So, not solely has there been an general increase in macroalgae floor space of 13.4% per 12 months since 2003, that fee is growing over time; since 2013, that fee grew to 16.7% per 12 months (Figure 2D).  

This elevated fee of algal blooms coincides with accelerated ocean warming, significantly since 2010. This means that we’ve maybe reached a tipping level in ocean temperatures resulting in situations that favor macroalgae growth. Warmer waters can pace up algal growth whereas additionally altering ocean circulation patterns that distribute vitamins that algae need to grow. 

Floating algae protecting such giant areas of the ocean may have vital ecological impacts. It will lower the quantity of gentle in the water column reaching seagrass and corals, which is able to negatively influence these organisms’ growth. Also, more seaweed and much less seagrass or coral is sure to influence marine food webs in methods we’ve but to analyze. This may additionally have an effect on how the ocean shops carbon, doubtlessly weakening its skill to behave as a long-term carbon sink.

There may also be widespread financial and societal impacts. Large piles of seaweed washing onto tropical seashores will doubtless influence tourism. Who would need to swim or calm down at a seaside with giant piles of rotting (and smelly) seaweed? Increased seaweed may also influence fisheries by making it tougher for fishermen to navigate their native waters and by altering the place fish could also be discovered.

Seaweed blooms might seem to be a native nuisance, or simply one thing that ruins your seaside day. But this examine demonstrated that they are additionally a seen symptom of a bigger transformation underway in the international ocean. These blooms offer each a warning of our quickly altering world in addition to an alternative to raised perceive and handle these modifications. Whether by way of improved monitoring, decreasing nutrient air pollution, or defending weak ecosystems like seagrasses and coral reefs, there are some ways we are able to reply to this new risk to ocean ecosystems.