Zebra mussel (Dreissena polymorpha) eradication efforts in Christmas Lake, Minnesota

Lund K, Bloodsworth Cattoor K, Fieldseth E, Sweet J, McCartney MA. 2017. Zebra mussel (Dreissena polymorpha) eradication efforts in Christmas Lake, Minnesota. Lake Reserv Manage. 34:7–20. In August 2014, an early-detection program discovered a new infestation of zebra mussels (Dreissena polymorpha) in Christmas Lake, a small (1.072 km²) lake near the Twin Cities, Minnesota. Initial surveys suggested a small introduction localized near a public boat access, prompting a rapid response from local and state partners. In 2014–2015, 7 treatments (areas from 243 m² to 41,000 m²) were made with 3 different molluscicides (Zequanox, EarthTec QZ, potash); each used in few prior efforts in open waters. Toxicity bioassays (mussels caged on site and in aquaria) were used to help guide treatments. Intensive SCUBA belt transect and settlement sampler surveys up to one year post-treatment showed that of the ∼5500 mussels in the first treatment area (and 10 found just outside it in May 2015), no survivors were recovered. Yet despite rapid coordinated response, in October 2016, 16 mussels were found on structures removed from untreated sites across the lake. The range of shell lengths suggested a remnant population whose larvae had dispersed and settled in scattered locations, and/or dispersal of juveniles from the infestation site. Lessons from this 1 yr eradication attempt highlight the challenges with partial-lake treatments: locating mussels at low densities, containing them within treatment areas large enough given detection uncertainty, and maintaining lethal molluscicide concentrations. Nevertheless, new understanding of these issues, and experience with toxicity and dosing protocols will advise future work. This case study demonstrates the importance of early detection, immediate responses, post-treatment monitoring, and effective cooperation among partners.