Invasive carpet sea squirt spreading in Kosterhavet

The invasive carpet sea squirt (filtsjöpung), known as “sea vomit,” is rapidly spreading across the seafloor in Kosterhavet National Park, smothering organisms beneath it. Authorities say budget cuts have hampered monitoring and control, but they are now examining ways to slow the outbreak.

AI Comment from GPT 5:

The post describes a rapid expansion of the invasive carpet sea squirt (Didemnum vexillum) across the seafloor in Kosterhavet National Park, with observers noting large new patches this year and local authorities warning that limited funding has delayed detection and constrained control efforts. Officials are now assessing measures to slow the spread, though they caution it may soon be impossible to stop.

The related posts show how similar patterns have unfolded nearby and abroad, helping contextualize the Kosterhavet surge. In southwestern Norway, divers first documented D. vexillum in 2020 and built a local monitoring effort as colonies established along vertical walls at depth, indicating a recent arrival and rapid foothold (Monitoring program tracks invasive (Didemnum vexillum) or “marine vomit”). By 2021, observations along Norway’s west coast tied wider spread to boat traffic and hull fouling, and noted risks to marine vegetation and aquaculture, with authorities convening to discuss management and advising against flushing fouled hulls in infested waters (Marine vomit spread along the western coast of Norway). Norwegian researchers have warned since the first detections that once D. vexillum becomes established, it is difficult to halt, and hull transport is a likely pathway (Feared sea urchin has come to Norway – Spreading like a plague). Beyond Scandinavia, Alaska’s experience underscores the species’ fast growth, ability to smother other organisms, and the urgency of early delimitation and feasibility assessment for eradication once detected (New Invasive Species Detected in Alaska). An Alaska legislative effort further highlights the value of rapid, coordinated response frameworks for aquatic invasions, which could inform regional approaches to managing D. vexillum’s spread in the North Atlantic (Invasive species bill introduced to Alaska legislature). Together these posts illuminate the Kosterhavet observation by showing recurring pathways, impacts on benthic communities and aquaculture, and the management challenges that arise when surveillance and rapid response capacity are limited.