From poetry to music to movies, we’re always hearing about the “deep blue sea.” But the seas aren’t always deep blue. And sometimes, they’re not blue at all. They can be green, brown, or other colors. And each color can tell us something about what’s happening in that part of the sea.

Understanding what the colors are telling us is one goal of PACE—Plankton, Aerosol, Cloud, Ocean Ecosystem—a NASA satellite that launched in February.

[3, 2, 1, booster ignition ... Full-power engines and liftoff of the Falcon 9 and PACE—helping keep pace with our ever-changing ocean and atmosphere...]

The mission is studying how the oceans and atmosphere interact, tracking their health, charting marine resources, and more. And ocean color plays a big role in all of that.

The water can be tinted by tiny organisms known as phytoplankton. Some of them turn the water green—a result of the chlorophyll they use to convert sunlight to energy. Plankton attract fish and other large animals. So keeping an eye on the color can help scientists track the health of fisheries.

Massive blooms of some types of algae, on the other hand, can stain the water brown or red. They may use up much of the oxygen in the water, turning a region into a “dead zone” where not many other organisms can live. They can also produce toxins that make shellfish dangerous to eat. So tracking the blooms—by looking for their colors from space—can help keep people safe.

For the seagrass beds of southern Texas, rising sea level may be a case of give and take—or make that take and give. Higher waters are killing off some seagrass. But as the water rises even higher, newly submerged land has the potential to increase the total seagrass area.

Seagrass is important for many coastal ecosystems. It can protect the coast from storms, filter pollution from runoff, and provide habitat and food for fish and other life. So losing seagrass is a big deal.

Researchers at the University of Texas Marine Science Institute studied beds in Upper Laguna Madre—a narrow estuary behind Padre Island. They looked at the beds today, and examined records from the past three decades.

Sea level in the region is rising much faster than the global average—roughly half an inch to an inch per year. As the water rises, less sunlight reaches the bottom—a big problem for seagrasses. Because of the deeper waters, two species of seagrass have vanished since 2018 at one study location. A check on a wider area showed that seagrass had disappeared at almost a quarter of the sampled locations.

On the other hand, seagrass may colonize newly submerged regions. That could expand its total habitat by as much as 25 square miles by 2050.

Not every seagrass habitat will be that prolific. Beds in much of the world are hemmed in by development, so they have no place to go. For those regions, there won’t be much give and take—rising sea level will be all take.

The “beards” of marine mussels aren’t just a fashion statement. They anchor the mussels to the sea floor, attach to each other to form large “beds,” and hold out potential invaders. They’re also playing a role in materials research—scientists study the beards to learn how to make water-proof glue for many applications.

The beards consist of a bundle of about 20 to 60 threads known as a byssus. The threads radiate outward from the mussel’s “foot.” Each thread is tipped with a biological superglue—a combination of proteins from the mussel and metals from the water.

Mussels use the byssus to anchor themselves to the bottom, where they wait for tiny prey organisms to float through their shells. The threads are strong but flexible, so they allow the mussels to sway with the tides. The glue never dissolves in the water. The mussels can use the threads to move along the bottom; they anchor one thread, then “reel” it in to shift position.

When the mussels are threatened, though, they let go in a hurry. Tiny hairlike structures on the bottom of the foot beat rapidly, detaching the byssus from the mussel’s body. The mussel grows a new one in just a few hours.

Scientists are studying the byssus to help develop ways to attach sensors or implants to the human body. They’re also looking for ways to overcome the glue to prevent mussels—especially freshwater species—from fouling underwater outlets or other structures—getting free of some “sticky” threads.