Soft sediment as a constraint on the spread of the zebra mussel in western Lake Erie: Processes and impacts

Abstract

The zebra mussel (Dreissena), inadvertently introduced to the Great Lakes in 1986, has since expanded to cover most of the shallow-water, hard substrates in Lakes Erie and Ontario. Colony densities exceed 300,000 per m2 in some bedrock areas of western Lake Erie. The objective of this study was to investigate the spread of zebra mussel onto soft sediment areas of the western basin of Lake Erie and to identify natural controls on the large-scale colonization of such sediments. Combined side scan sonar, underwater video imagery, and direct diver observation showed three modes of viable zebra mussel colonies in soft substrates: 1) attachment to zebra mussel shell debris deposited in linear troughs (stripes); 2) attachment to shells built up over hard substrates intermittently covered by soft sediments (footballs); and 3) as isolated clumps (druses) attached to dropstones, unionid clams, or their shells. Their spatial distribution suggests that zebra mussel expansion onto soft sediments is supplied primarily by nearby hard substrate areas. Zebra mussel populations living on soft sediment have the normal size distribution as those found on hard surfaces, often with a bimodal or trimodal character, representing cohorts of different ages. At the sites studied, there was a large proportion of dead shells, suggesting colonization over an extended period, as well as a relatively high mortality rate due to burial by periodic catastrophic sedimentation after storms. This vulnerability and the need to be near to source areas make it unlikely that the zebra mussel (D. polymorpha) will continue to expand into areas of soft sediment remote from hard substrate areas. The impact of the zebra mussel colonies on important textural properties of the substrate was not dramatic, but median grain diameter was significantly finer, organic carbon significantly higher, and sediment consistency more clayey below zebra mussel mats. Metal content was generally higher in the samples below zebra mussel mats, but the differences were statistically significant only in the case of iron and maganese. However, the sediment concentrations of metals at all sites were much greater than those at the remote Mid-basin site that was barren of zebra mussels, suggesting an overall metal enrichment near zebra mussel colonies.

Soluble nitrogen and phosphorus excretion of exotic freshwater mussels (Dreissena spp.): potential impacts for nutrient remineralisation in western Lake Erie

“…Mussel densities at this site in 1998 and 2003 were near 20 000 m −2 (22 239 and 20 847 m −2 , respectively; Pontius, 2000; Fig. 3a), whereas other studies have found much lower mussel densities (<500 m −2 on mud; Coakley et al. , 2002) or much higher (270 000 m −2 on rocks, MacIsaac et al.…”

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

“…Between 1999 and 2004, lakewide biomass of zebra and quagga mussels ranged from 14 kt (1,000s of metric tones) in 1999 to a peak of 43 kt in 2001 and returned to 14 kt in 2003 (Madenjian et al 2005a). These lakewide estimates are likely conservative because trawls are not fished over the hard substrate on which zebra mussels prefer to attach Coakley et al 2002). Zebra mussel biomass was not separated from quagga mussel biomass in these trawl surveys, but observations suggest that the proportion of quagga mussels has been increasing in recent years.…”

Resource contributions from dreissenid mussels to the benthic algae Lyngbya wollei (Cyanobacteria) and Cladophora glomerata (Chlorophyta)

“…Unfiltered lake water with naturally occurring plankton was refreshed about twice a week in the stock tubs of Dreissena to provide food and other resources. The quantity of undamaged Dreissena added to the experimental tanks represented the density of Dreissena on soft sediments in Lake Erie (i.e., 3,400 individuals m -2 (Coakley et al, 2002) or 116 individuals/tank). Empty Dreissena clusters were made by attaching dead Dreissena shells together using small beads of non-toxic glue to provide the same physical structure as live Dreissena, without any contribution of resources from active metabolism.…”

“…Shallow freshwater environments and areas of dense algal mats can become depleted in CO 2 (Stevenson, 1988;Stevenson et al, 2004), which can restrict photosynthesis if the alga cannot utilize HCO 3 -as well as CO 2 (Cheney & Hough, 1983). Dreissena aggregations can have a very high density (Coakley et al, 2002); consequently, CO 2 produced by their respiration and the decomposition of their waste may potentially increase CO 2 and soluble organic carbon within the benthos. Although studies have shown that Dreissena can promote benthic algal blooms through increased light, P, and N, the relative importance of potential flows of macronutrients and carbon (C) from Dreissena to algae on controlling benthic primary production has not been shown.…”