A new study published recently in Scientific Reports sheds light on how the green alga Ulva, common on shores around the world, can suddenly explode into massive blooms known as “Green Tides.”
Ulva is incredibly adaptable. It can switch between different ways of using carbon as it grows, which helps it thrive even when conditions become crowded and nutrients are high. By compiling isotopic measurements of Ulva from around the world, Javier Lloret, assistant professor at the University of Maryland Center for Environmental Science’s Horn Point Laboratory, found that this alga shows an unusually wide range in its carbon isotope fingerprints.
That surprising pattern points to two modes of growth:
- A normal mode, when algal densities are low and conditions are not limiting
- A bloom mode, when fast growth and crowded conditions push Ulva to use carbon differently, creating a distinct chemical signature
To test this in the field, Lloret examined Ulva in several New England estuaries. In places with dense mats of seaweed and poorer water quality, Ulva consistently showed the “bloom-mode” carbon signature.
This means that Ulva’s carbon fingerprint can serve as a new indicator of water quality problems, helping scientists and managers identify when coastal ecosystems are experiencing the early stages of eutrophication, even before large blooms appear. The carbon signature can be detected by a low-cost laboratory test, making it an accessible strategy for determining when intervention is necessary.
“Understanding these growth modes helps explain how Ulva can form some of the largest algal blooms on Earth,” Lloret said. “But it also gives us a powerful tool for tracking changes in our coastal waters.”
