by Emily Li
Smithsonian biologists are on the trail of invasive ascidians. But with roughly 2300 species worldwide, describing these marine filter feeders (also known as “tunicates” or “sea squirts”) for a Most Wanted sign is tricky. Some ascidians are solitary; some are social. Some breed sexually, some asexually. Some, like Botrylloides magnicoecum, form large colonies of what look like octopus tentacles ringed in gold and highlighter blue. Others, like Rhopalaea crassa, resemble a cross between ghostly butterfly cocoons and pastel-colored pencil grips, while Polycarpa aurata is bulbous and mustard-yellow, with navy-blue veins that flare into trumpets.
When they invade new territory, ascidians can leave trails of damage in their wakes—but not always in ways scientists predict. In a new study published in the July issue of Marine Biology, a team of Smithsonian researchers, including marine ecologist Christina Simkanin of the Smithsonian Environmental Research Center (SERC), tracked their invasions across North America.
What they found seemed simple at first: North America’s 26 non-native ascidian species have spread so much they’re now established along nearly 3000 miles of its coastlines. But a few surprises were hiding in the details.