First Documentation of the Invasive Species Craspedacusta sowerbyi in Lake Sammamish 2021

Principal Researcher: Andrew Vasey, Student at the University of Washington, College of the Environment

Abstract: This paper documents the first discovery of the invasive species C. sowerbyi (Fresh Water Jelly Fish) in Lake Sammamish located in King County, Washington on July 24th, 2021, and subsequently reported to the USGS Non-Indigenous Species Program. The observation followed record air and water temperatures in the Lake Sammamish watershed, which aligns with the projected range expansion of C.sowerbyi into higher latitude regions resulting from climate change driven temperature increases, predicted by(Marchessaux et al, 2021) and (Rahel and Olden, 2008).

Lake Sammamish: Lake Sammamish is the 6th largest lake in Washington, covering 4897 acres over its 8-mile length, with an average depth of 58 feet (Lake Sammamish Monitoring Overview — King County). Prior to this observation, C. sowerbyi had not been identified in Lake Sammamish waters per USGS tracking.

Local air temperatures in the area reached record highs 28 days prior to the sighting. From 6/1 to 7/28 I measured air temperatures using an Ambient Weather WS-2902 located 10 ft above the surface of Lake Sammamish. From 6/26 to 6/28 the recorded 24-hour average temperatures ranged from 82.3°F to 88.0°F, and maximum temperature readings ranged from 99.7°F to 106.5°F.

Figure 1-Graph of 24-hour average air temperature and daily high temperature at Lake Sammamish

Observations Made on July 24th:

On July 24th, 2021, while scuba diving to explore fish habitat in the “sunken forest” area of Lake Sammamish two individuals of the species C. sowerbyi were observed and photographed at 5 to 6 meters of depth in a water column 14.5 meters deep.

Individual #1 at depth of 5 meters

Individual #2 at 6 Meters

Individual #2 Close Up

There was a significant thermocline at the site, with warm water with decent visibility in the top 25 ft, and cold water with nearly no visibility due to sediments down to the bottom at 47 ft. As a result, observations were only made above the thermocline.

Subsequent sightings of C. sowerbyi in Lake Sammamish were made by others and documented on 8/5/2021 and 9/14/2021 further confirming that this invasive species is now established in Lake Sammamish waters.

Location of Observation, Map Courtesy of Google

References:

“Lake Sammamish Monitoring Overview — King County.” Lake Sammamish Monitoring Overview, King County Water and Land Services, green2.kingcounty.gov/lakes/LakeSammamish.aspx. Accessed 27 Dec. 2021.

Marchessaux, G., Lüskow, F., Sarà, G. et al. Predicting the current and future global distribution of the invasive freshwater hydrozoan Craspedacusta sowerbii. Sci Rep 11, 23099 (2021). https://doi.org/10.1038/s41598-021-02525-3

Rahel FJ, Olden JD. Assessing the effects of climate change on aquatic invasive species. Conserv Biol. 2008 Jun;22(3):521–33. doi: 10.1111/j.1523–1739.2008.00950.x. PMID: 18577081.