Larson Courtney E, Barge Jonathan T, Hatzenbuhler Chelsea L, Hoffman Joel C, Peterson Greg S, Pilgrim Erik M, Wiechman Barry, Rees Christopher B, Trebitz Anett S
U.S. Environmental Protection Agency, Office of Research and Development, Duluth, MN, United States.
Department of Biology, University of Minnesota Duluth, Duluth, MN, United States.
Front Mar Sci. 2022 Feb 21;9:1-818738. doi: 10.3389/fmars.2022.818738.
Coastal waters of Lake Superior are generally inhospitable to the establishment of invasive . mussels (both and ). have inhabited the Saint Louis River estuary (SLRE; largest commercial port in the Laurentian Great Lakes) for over three decades, but only in the last few years have small colonies been found in the Apostle Islands National Lakeshore (APIS, an archipelago situated 85 km to the east of SLRE) A 2017 survey determined a low abundance spatial distribution in APIS, with the largest colonies on the north and west islands which suggested potential veliger transport from the SLRE longshore currents. Our objective in this study was to determine if veligers are transported by currents at low densities along the south shore of Lake Superior from the SLRE to APIS. To do so, we used both eDNA (water and passive substrate samples) and zooplankton collection methods at eight sites evenly spaced between the SLRE and APIS with three sampling times over five weeks. veligers were consistently detected along the south shore, although at low abundances (veligers per m range = 0-690, median = 8), and for every 1 km increase in distance from the SLRE, both veliger counts and water eDNA copy numbers decreased on average by 5 and 7%, respectively. (suited to estuary habitats) was detected two times more than (better suited to deep-lake habitats). There was not a trend in the veliger size distribution along the south shore, and temperature and calcium concentrations fluctuated around the threshold for veliger and adult development, averaging 11.0°C and 14.8 ppm, respectively. Three zooplankton taxa representative of the estuary community-, , and copepodites-decreased as the distance from the SLRE increased mirroring veliger abundance patterns. Findings represent multiple sources of evidence of a propagule "conveyor belt" for along the south shore of Lake Superior. We conclude that veligers are functioning as a propagule, using coastal currents to spread from the point of invasion, thereby traversing coastal habitat previously reported as inhospitable to distant habitats suitable for colonization.
苏必利尔湖的沿海水域通常不利于入侵贻贝（两种贻贝）的生存。贻贝已在圣路易斯河河口（SLRE；劳伦琴五大湖最大的商业港口）栖息了三十多年，但直到最近几年，才在使徒群岛国家湖滨区（APIS，位于SLRE以东85公里处的一个群岛）发现了小群体。2017年的一项调查确定了APIS中贻贝的低丰度和空间分布，最大的群体位于北部和西部岛屿，这表明可能是通过沿岸流从SLRE运输了面盘幼虫。我们在本研究中的目标是确定面盘幼虫是否会以低密度通过水流沿着苏必利尔湖南岸从SLRE运输到APIS。为此，我们在SLRE和APIS之间均匀分布的八个地点使用了环境DNA（水样和被动基质样本）和浮游动物采集方法，在五周内进行了三次采样。尽管丰度较低（每立方米面盘幼虫范围 = 0 - 690，中位数 = 8），但在南岸始终能检测到面盘幼虫，并且从SLRE起每增加1公里距离，面盘幼虫数量和水样环境DNA拷贝数平均分别下降5%和7%。适合河口栖息地的贻贝被检测到的次数比更适合深湖栖息地的贻贝多两倍。南岸面盘幼虫的大小分布没有趋势，温度和钙浓度在面盘幼虫和成年贻贝发育的阈值附近波动，平均分别为11.0°C和14.8 ppm。代表河口群落的三种浮游动物类群——哲水蚤、剑水蚤和桡足幼体——随着与SLRE距离的增加而减少，这与面盘幼虫的丰度模式相似。研究结果代表了苏必利尔湖南岸贻贝繁殖体“传送带”的多种证据来源。我们得出结论，面盘幼虫作为繁殖体发挥作用，利用沿岸流从入侵点扩散，从而穿越先前报道的不利于生存的沿海栖息地，到达适合定殖的遥远栖息地。
