Today’s Image of the Day from NASA Earth Observatory features a large phytoplankton bloom in the Gulf of Maine.

The image was captured on June 21, 2025, by the Ocean Color Instrument (OCI) on NASA’s PACE satellite. 

“In summer 2025, waters in the Gulf of Maine popped with vivid swirls of blue and green. The cause was a massive bloom of phytoplankton – microscopic plant-like organisms that often float near the ocean surface,” noted NASA.

“Scientists say it was one of the largest blooms of its kind to show up in the Gulf’s waters in recent years.”

Giant bloom in the Gulf of Maine 

Catherine Mitchell is a satellite oceanographer at Bigelow Laboratory for Ocean Sciences. She noted that the Gulf of Maine bloom contained coccolithophores, a type of phytoplankton that makes the water appear milky blue.

“The tiny organisms, along with other types of phytoplankton, including diatoms that bloom here in spring, lie at the base of the marine food web,” explained NASA.

“Their presence – or absence – in Gulf of Maine waters can affect the entire ecosystem, from finfish to shellfish, and the region’s fisheries that depend on them.”

Shifting conditions and plankton communities 

Mitchell said that coccolithophore blooms like this one became less common in the Gulf’s waters starting around 2010. But in recent years, they’ve started to come back. 

Scientists have also seen more dinoflagellates (a type of phytoplankton that move with tiny tails) and an overall drop in phytoplankton productivity over the past few decades.

These changes in plankton are linked to shifting ocean conditions. For instance, heavy rainfall from 2006 to 2009 made the Gulf’s waters fresher. Then, starting in 2008, warm water from deep in the North Atlantic began heating the Gulf from the bottom up. 

However, by spring 2025, bottom-water temperatures were cooler than they’ve been in 20 years.

Ongoing research efforts

“The relationship between these changing water conditions and phytoplankton communities in the gulf remains unclear, but ongoing research could begin to provide some answers,” noted NASA.

“In fact, Mitchell and colleagues scrutinized this PACE image just days before heading out on a research expedition to study the bloom and other ocean properties up close. The cruise, the third so far this year, offers scientists the chance to validate ocean color data collected by PACE with real-world ocean samples.”

Mitchell pointed out that a major benefit of the PACE satellite is its ability to “see the rainbow,” which makes it easier for scientists to distinguish between groups of phytoplankton.

“With our continuing field measurements, we will validate ocean color observations from PACE, enabling satellite observations in the Gulf of Maine and supporting the region’s fisheries and aquaculture industries.”

Vital signs of ocean health

Phytoplankton blooms like the one captured in the Gulf of Maine are vital signs of ocean health. These microscopic organisms form the foundation of marine food webs, feeding everything from tiny zooplankton to large fish, whales, and seabirds. 

When conditions are right – such as warm temperatures, abundant sunlight, and available nutrients – phytoplankton populations can grow rapidly, creating colorful blooms that are visible from space.

The Gulf of Maine is particularly sensitive to environmental change. Located at the intersection of cold northern currents and warmer waters from the south, it’s a dynamic ecosystem where small shifts in temperature or salinity can have outsized effects. 

This region is also one of the fastest-warming ocean areas on the planet, with temperatures rising more than three times the global ocean average in some years.

Forecasting changes with ocean monitoring 

Changes in water temperature and salinity have ripple effects across the food chain. Warmer waters can favor certain types of phytoplankton over others, shifting the balance of species in ways that affect what fish and shellfish are available to predators – and to the region’s fisheries. 

For example, coccolithophores may thrive in clearer, warmer waters, while traditional spring-blooming diatoms do better in colder, more nutrient-rich conditions.

Long-term monitoring is essential to understand and predict these shifts. Satellites like PACE provide a global view of ocean color, which reflects the presence and composition of phytoplankton. 

By combining these observations with ship-based sampling, scientists can get a more complete picture of how plankton communities are evolving and how that affects everything from carbon cycling to fisheries sustainability.

Warming in the Gulf of Maine 

The Gulf’s warming trend has already caused noticeable ecological changes. Some species of fish have moved farther north or into deeper waters in search of cooler temperatures. 

Lobsters, a key commercial species, have shifted their range as well. Meanwhile, harmful algal blooms – caused by certain types of phytoplankton – have become more frequent in some parts of the Gulf, threatening shellfish harvests and public health.

Scientists are working to better predict how blooms will respond to future climate conditions. 

Understanding which species are likely to dominate under warmer, fresher, or more acidic conditions can help predict changes in fish stocks, shellfish safety, and ecosystem stability. 

This kind of forecasting is especially important in the Gulf of Maine, where marine resources are closely tied to local economies.

Image Credit: NASA Earth Observatory 

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