Dreissena veligers in western Lake Superior – Inference from new low-density detection

Abstract

The notion that Lake Superior proper is inhospitable to dreissenid mussel survival has been challenged by recent finds on shipwrecks and rocky reefs in the Apostle Islands region. Motivated by concerns surrounding these finds, we conducted an intensive sampling campaign of Apostle Islands waters in 2017 to understand Dreissena prevalence and distribution. The 100-site effort combined random and targeted sites and collected zooplankton, benthos, video, environmental DNA, and supporting water quality data. We did not find settled Dreissena in any video footage or benthos samples, and quantitative PCR applied to eDNA samples was negative for Dreissena. Dreissena veligers were found in almost half the zooplankton samples but at orders of magnitude lower densities than reported from other Laurentian Great Lakes. Veligers were most prevalent around the western islands and associated with shallower depths and slightly higher phosphorus and chlorophyll, but did not spatially match known (still very localized) settled Dreissena colonies. This is the first study to conduct veliger-targeted sampling in western Lake Superior and the first to report consistent detection of veligers there. We speculate that these Apostle Islands veligers are not a new locally-spawned component of the zooplankton community, but instead are transported from an established population in the St. Louis River estuary (~100 km away) by longshore currents; i.e., low-density propagule pressure that may have been present for years. Small-mesh zooplankton data collected along a gradient from the Apostle Islands to the St. Louis River estuary and enumerated with thorough veliger searching would help elucidate these alternatives.

Physical Circulation in the Coastal Zone of a Large Lake Controls the Benthic Biological Distribution

“…As an example, the threshold conductivity of 140 μS/cm required for dreissenid mussel growth equals to about 14.8 mg/L of calcium. Trebitz et al (2019) reported a similar calcium level (ranged from 11 to 14 mg/L) associated with the low detection of dreissenid mussels in SW Lake Superior. Adult dreissenid mussels or their DNA were not detected after extensive sampling in SW Lake Superior.…”

Advanced molecular-based surveillance of quagga and zebra mussels: A review of environmental DNA/RNA (eDNA/eRNA) studies and considerations for future directions

“…A number of possible explanations were provided to account for lower detection success during the spring months, including increased dilution due to snow-melt and potential cold-season (winter) die-off. Support for the hypothesis that dilution plays a significant role in the success of QM-ZM eDNA surveys was later demonstrated by Trebitz et al (2019). Akin to Peñarrubia et al (2016), the increased detection success, observed by Gingera et al (2017) in autumn, was attributed to QM-ZM life history, where whole-veliger presence, post-spring/summer spawning, likely contributes to ease of eDNA detection.…”

“…Three alternative -and high-performing (Sepulveda et al 2020a) -probe-based assays developed by Gingera et al (2017) have become some of the most prevalently used qPCR assays in North American QM-ZM eDNA surveillance efforts (e.g. Devlin Sepulveda et al 2019Sepulveda et al , 2020aTrebitz et al 2019;Watts 2020;Marshall et al 2021). These assays are commonly cited in literature as ZEBCOI, ZEB-CYT and DRE16S (Table 3), with ZEBCOI and ZEBCYT being specific to ZM and DRE16S generically targeting both QM and ZM.…”

An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly

“…These likely represent declining or extirpated populations, particularly in watersheds converted to large-scale agriculture [ 47 ], and in habitats that are densely populated by Dreissena mussels [ 30 ]. The rocky surf zone habitats in Lake Superior remain largely mussel-free at present, but the recent appearance of established juvenile and adult Dreissena in the Apostle Islands, 90 km from their likely source in the St. Louis River estuary [ 116 ] indicates that long-distance dispersal during the planktonic veliger stage is occurring along the south shore. A low-density Dreissena population exists on the iron ore loading dock in Marquette’s upper harbor, just down-current of our research area.…”