We’ve got a lot on our plates here in the environmental office, but thankfully none of its invasive species! A group of students from the Hoonah City Schools just completed another round of the Plate Watch monitoring program to look for invasive tunicates growing in Hoonah Harbor, helping to ensure our waters stay as clean as possible.
Plate Watch is a collaboration between the Smithsonian Environmental Research Center (SERC) and 35 communities along the coast of Alaska, ranging from Metlakatla in the south to Utqiagvik in the north. Started in 2007, the project aims to understand how invasive invertebrates spread through novel regions and how climate change is likely to affect those processes moving forward. With waters that are warming twice as fast as the national average and increasing shipping due to a decrease in sea ice cover, Alaska has the potential for another ecological disaster that could be as damaging as the oil industry—invasive species spreading further and faster than ever seen before.
Tunicates are a type of marine invertebrate, in the same general category as crabs but instead of having a rigid shell to protect themselves, they have a soft covering called a tunic. They’re filter feeders, gobbling up plankton with their siphons and helping clean the water. They also have some truly bizarre biology, despite being our closest invertebrate cousins. Their hearts can switch the direction that blood flows through their bodies, though why exactly that’s useful is still a bit of a mystery. Some species of tunicates can develop from infancy to adulthood in a single day, which would make middle school for a tunicate fit cleanly between breakfast and lunch. Perhaps the most relevant is their ability to regrow parts of their bodies which most likely evolved because as sessile creatures they can’t evade predators. This ability has grown in interest recently, as it could be useful for human studies into stem cell treatments to help with spinal cord injuries.
The plates in Hoonah are located off the transient dock, which is one of the first place that hitchhikers from visiting boats would be likely to invade. Each partner site hangs a series of small PVC plates off the side of a local dock for three months to a year and then pulls them up to document them and identify the new critters that have moved in. In Hoonah, the project is primarily run by students, be it the Fisheries Management students during the school year or the Alaskan Youth Stewards over the summer. Regardless of who’s involved, it’s a fantastic hands-on opportunity for Hoonah youth to understand the creatures that help make Hoonah what it is and protect the waters from potential hazards.
Despite the discovery of the invasive Botryllid tunicates on Hoonah’s plates last fall, the plates pulled in September were clean—relatively speaking. They were still incrusted with all manners of barnacles, juvenile blue mussels and native tunicates. The clear and soft Corella Inflata, which grows in colonies of penny-sized blobs, got to be over three inches thick on one of the plates, and looked disconcertingly like Boba according to the high schoolers. The plates were also visited by a series of eager predators, including sea stars in a range of sizes and a pair of almost iridescent White-and-Orange-Tipped nudibranchs.
Not only does Plate Watch emphasize why it’s important to regularly clean the hulls of boats, it’s also a provides valuable scientific information how marine invertebrates travel and what conditions they prefer living in. In Dora Bay, a remote settlement on Prince of Wales that receives no regular boat traffic and where the annual assemblage of visitors could comfortably eat dinner together, botryllids were none the less documented, indicating that even small amounts of larvae brought in can lead to tunicate growth.
Invasive tunicates, such as Didemnum vexillum, more commonly known as rock vomit have already started causing problems in Alaska. A tan slime, it covers sea floors, crab pots, nets, and anything else it can get its oozing body on. It’s not just gross though, because it also grows to cover eelgrass beds, a critical habitat for Dungeness crabs and salmon fry. Rock vomit has been well documented in several harbors in Sitka, and there are currently experiments there to determine the best ways to kill it off. Like all invasive species though, the best way to treat it is to catch it early, before an infestation can take hold, which is exactly what Plate Watch aims to do.