The non-indigenous colonial tunicate Didemnum vexillum plagues many shellfish aquaculture operations around the world by smothering crop and gear and displacing juvenile bivalves. There are two populations of D. vexillum in Oregon, but little is known regarding their spatial extent, seasonal dynamics, annual variability, reproductive biology, or ecology. SCUBA divers monitored the seasonal variation and spatial extent of the nascent D. vexillum population in its current foothold at Umpqua Aquaculture, a longline oyster farm adjacent to Winchester Bay, Oregon. From May 2011 to November 2016, divers performed biannual subtidal surveys to measure the cover of D. vexillum on anchor lines. We found that this population of D. vexillum exhibited extensive fluctuation in colony during this period, especially between fall and spring. With one exception, cover was greater in the fall than the spring, though this fluctuation cannot be explained by our proxies for salinity or temperature. Seasonally, on average, D. vexillum covered the greatest proportion of line between 5.5 and 6.0 m depth in both the spring (37.5 ± 18.8%) and fall (45.1 ± 16.1%). During individual surveys, the depth of maximum percent D. vexillum cover was more variable, spanning ~ 4.5–6.5 m depth. Overall, we document a net increase in D. vexillum cover at Umpqua Aquaculture between the first and last surveys during the 5-year period. This study is the first published multi-year analysis of D. vexillum in Oregon and represents the longest continuous monitoring period of an in situ population of D. vexillum to date.

非土著殖民地被膜Didemnum vexillum窒息了世界各地的许多贝类水产养殖业，窒息了农作物和渔具，并移居了幼年的双壳类。俄勒冈州有两个D. vexillum种群，但关于它们的空间范围，季节动态，年度变化，生殖生物学或生态学知之甚少。SCUBA的潜水员在俄勒冈州温彻斯特湾附近的延绳牡蛎养殖场Umpqua Aquaculture监测其目前立足点的新生D. vexillum种群的季节性变化和空间范围。从2011年5月到2016年11月，潜水员每两年进行一次潮下调查，以测量锚索上的D. vexillum覆盖度。我们发现这个人口在此期间，尤其是在秋季和春季之间，维氏菌在菌落中表现出广泛的波动。除了一个例外，秋天的覆盖率大于春天的覆盖率，尽管这种波动不能用我们的盐度或温度指标来解释。在春季（37.5±18.8％）和秋季（45.1±16.1％）的季节中，平均而言，D。vexillum在季节上平均覆盖线段的最大比例。在单独的调查中，最大的D. vexillum覆盖深度的变化更大，跨度约为4.5-6.5 m。总体而言，我们记录了在5年内的第一次和最后一次调查之间，Umpqua水产养殖的D. vexillum覆盖量净增加。这项研究是第一个发表的多年期分析俄勒冈州的D. vexillum，代表了迄今为止D. vexillum原位种群的最长连续监测期。