A team of scientists have discovered two populations of a new species record of Avrainvillea erecta. The team included several members of the University of Hawai‘i Department of Botany, doctoral student Rachael Wade, postdoctoral researcher Dr. Heather Spalding, and faculty member Dr. Alison Sherwood, as well as three scientists from state and federal agencies, a local commercial diver, and a postdoctoral fellow at the Smithsonian Marine Station at Fort Pierce. Using both physical and genetic features of the seaweed, the team determined that the new arrival is most likely Avrainvillea erecta. However, much like the previous invader Avrainvillea amadelpha, the identification was challenging. “There has not been very much work done on this group of green algae and it is very challenging because it is quite variable in how it presents itself. As a result, it’s difficult to conclusively identify these species until a more thorough genetic reference framework can be put together” said Rachael Wade, who is building such a framework through her dissertation research.

The mode of this alga’s introduction is unknown. Given the close proximity of the two populations to urbanized estuaries and major seaports, it is possible that the seaweed was introduced via regular boat traffic. It is also possible that the seaweed was introduced as debris following the 2011 Tohuku earthquake and resulting tsunami.

Regardless of the species identification of both Avrainvillea species, these seaweeds are of concern because of their potential threat to Hawai‘i’s marine environments. Avrainvillea amadelpha has overgrown shallow reefs in Maunalua Bay and outcompeted seagrass meadows. While the impacts of Avrainvillea erecta are unknown and require further study, it may have similar competitive traits and therefore may negatively impact Hawai‘i’s reefs. Luckily, the two species are relatively easy to tell apart and identify in the water. Avrainvillea amadelpha often forms a patchy carpet on either rock or in sand with several spoon- or paddle-shaped blades per patch and is generally a dark grayish or brownish green in color. In contrast, Avrainvillea erecta generally has one brilliant green, kidney-shaped blade and a long, conical holdfast and is only found in sandy habitats. “We encourage everyone to keep an eye out for this new species as they spend time in the water. It’s important that we continue to track this species as it spreads.” says Dr. Heather Spalding.

If you think you’ve sighted either of these species of seaweed, please consider making a report through Eyes on the Reef to document your sighting, and contact Rachael Wade.

Rachael Wade, MS, PhD candidate

Images: A. amadelpha. Photo credit: R. Wade A. cf. erect. Photo credit: H. Spalding A. amadelpha in Hawai‘i environments. Photo credit: H. Spalding A. cf. erecta in Hawai‘i environments. Photo credit: S. Rowley