Abstract
The control of the highly invasive zebra mussel (Dreissena polymorpha) has been flagged as a priority but success has been variable. A better understanding of the growth and drivers of settlement of zebra mussel is necessary for a more efficient management of this invasive species, but seasonal data are still relatively scant. We monitored the seasonal changes in settlement rates, density, and growth of zebra mussel in artificial substrates over one year in Cardiff Bay (UK), an artificial amenity lake invaded by zebra mussels in 2003 and where the species is rapidly expanding. Mean settling rates varied from 4,200 to 6,200 mussel m-2 over June to September mirroring changes in water temperature, and peaked at 17,960 mussels m-2, the highest density reported in Britain. Density was highest at the deepest panels (3 m). Growth varied significantly among sampling stations, with growth taking place during the summer and ceasing during winter and spring. Mixture analysis reveals the existence of multiple cohorts displaying different growth and settling rates and that follow different density dependent mechanisms, being positive density-dependent at low densities, and negative density-dependent at high densities. We suggest this creates the conditions necessary for source and sink metapopulations to develop which may need to be taken into account in management. Targeting mussels for removal in deep waters during the summer and early autumn might prove beneficial, but the existence of contrasting density-dependent mechanisms suggests that removal may be beneficial or counterproductive depending on local conditions.
Highlights
The zebra mussel (Dreissena polymorpha) is one of the most damaging aquatic invaders (Strayer, 2010), having been included in the list of the 100 world’s worst alien species (Lowe et al, 2000)
Similar failures have been reported in Deep Quarry (United States) (Whitledge et al, 2015) and in Christmas Lake (United States); in the last case the local eradication was successful, but zebra mussel were subsequently found outside the treated area (Lund et al, 2018)
Our study suggests that zebra mussel may be spatially structured into different cohorts that grow and settle at different rates
Summary
The zebra mussel (Dreissena polymorpha) is one of the most damaging aquatic invaders (Strayer, 2010), having been included in the list of the 100 world’s worst alien species (Lowe et al, 2000). The economic losses caused by zebra mussels can be considerable. In Lake George (United States), manual SCUBA diving removal during eight consecutive years eradicated zebra mussel from a private marina, but new small colonies appeared in other parts of the lake that required further control (Wimbush et al, 2009). OAFB (2009) reported the successful eradication of zebra mussel in lake Offutt (United States) using copper sulfate, in 2014 the species was found again in the lake (Britton, 2015). Similar failures have been reported in Deep Quarry (United States) (Whitledge et al, 2015) and in Christmas Lake (United States); in the last case the local eradication was successful, but zebra mussel were subsequently found outside the treated area (Lund et al, 2018)
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