1st record: Catskill (~RKM 200)/NY/Hudson River Estuary (Strayer et al. 1996; Center for Aquatic Resource Studies 2008)
Palmyra/NY/Erie Canal (1990, Center for Aquatic Resource Studies 2008); Amsterdam/NY/Mohawk River (1990, Center for Aquatic Resource Studies 2008); Troy (RKM 243)-West Haverstraw (RKM 65)/NY/Hudson river estuary (1992, Strayer et al. 1992; Walton 1996); Tappan Zee Bridge/NY/Hudson River (2006-2009, New York State Department of Transportation 2012, River Km 44)
|Alternate||Fisheries Accidental (not Oyster)|
|The Zebra Mussel invasion in the tidal fresh Hudson River resulted in an 85% decline in average phytoplankton biomass from 1987-1991 to 1993-1994. Light availability increased, as did phosphorus concentrations, while some planktonic grazers decreased. Flow characteristics of the river had not changed, supporting the hypothesis that grazing by the mussels was responsible (Caraco et al. 1997; Strayer et al. 1999). Laboratory grazing studies indicated that the biomass of zebra mussels could filter the tidal freshwater Hudson River in about two days (Roditi et al. 1996).The filtration rate has declined about 82% from its highest peak, in 1996, apparently due to increased mortality of mussels, and decreasing body size and biomass (Strayer et al. 2011). The toxic bloom-forming cyanobacterium Microcystis sp. was positively correlated with Zebra Mussel filtration rate, which is at odds with its behavior in other eutrophic systems, where high rates of Zebra Mussel grazing and nutrient release have promoted blooms of large, inedible colonies. Reasons for the absence of these cyanobacterial blooms in the Hudson River are not clear (Fernald et al. 2007).|
|Ecological Impact||Habitat Change|
|Grazing by the Zebra Mussels resulted in a 39% decrease in the light extinction coefficient, which indicates a sharp increase in light penetration, due to the removal of phytoplankton (Caraco et al. 1997; Strayer et al. 1999). Increased light penetration has resulted in an increase in shallow-water macrophytes (Strayer and Smith 2001; Strayer et al. 2011).|
|Filter-feeding by Zebra Mussels in the Hudson River resulted in a sharp decrease in the abundance of ciliates, rotifers, and copepod nauplii, apparently due to direct predation. The total biomass of zooplankton declined by about 70% after the invasion, due in part to predation (Pace et al. 1998).|
|Zebra mussels adversely affected native mussels of the family Unionidae (especially Anodonta implicata and Leptodea ochracea) by settling on them and fouling them. Densities of the native mussels, during the invasion, fell by 56% and numbers of recruits fell by 90% during 1992-1995. A decrease in condition of unionid mussels, and a decline in small sphaeriid (Pisidium spp., Sphaerium spp.) clams, not subject to fouling, suggests that competition for phytoplankton food was also affecting native bivalves (Strayer and Smith 1996; Strayer et al. 1999). Later analyses suggested that declines in recruitment and condition during the early years of the invasion were more closely related to zebra mussel filtration, and thus food competition, rather than fouling. From 2000 to 2005, the decline of native bivalves stopped, and abundances stabilized, even showing some recovery, but the mechanism for this is not clear (Strayer and Malcom 2006).Two groups of filter-feeding midge larvae, tanytarsini midges, and Chaoborus spp. declined during the zebra mussel invasion (Strayer and Smith 2001).|
|Ecological Impact||Trophic Cascade|
|The Zebra Mussel invasion in the Hudson River had wide-ranging effects on the estuary's food web. Effects on macrobenthos were complex. In deep-water samples, the abundance of benthic animals, mostly deposit-feeders, declined, because of the reduction of edible particles reaching the bottom. However, in shallow water, many groups of benthic invertebrates increased in abundance, probably because of increased growth of algae and macrophytes (Strayer et al. 1998; Strayer and Smith 2001). By 2000, populations of most deepwater macrobenthic species had recovered, apparently due to reduced biomass and decreased filtration rates of the Zebra Mussel population. However, shallow-water invertebrates remained at post-invasion levels (Strayer et al. 2011). |
The abundances of some fishes appear to have been affected by the mussel invasion. Some open-water species, particularly juveniles of Alewife (Alosa pseudoharengus) and White Perch (Morone americana) decreased during the invasion, while several littoral species increased, including Banded Killifish (Fundulus diaphanus), Bluegill (Lepomis macrochirus), Redbreast Sunfish (L. auritus), Smallmouth Bass (Micropterus dolomieu), and Tessellated Darter (Etheostoma olmstedi). Open-water fishes tended to shift their distribution downriver, while littoral fishes shifted upriver. Reduction in phytoplankton biomass and the planktonic part of the food web is believed to be the major factor in the shift in distribution and abundance of the open-water fishes, while the increase of shallow-water macrophytes and algae, as shelter for fishes and their prey, due to increased light penetration has benefited the littoral fishes (Strayer et al. 2004). Regions of the upper Hudson estuary witn more intense Zebra Mussel grazing had poor condtion and lower gut volume of Striped Bass (Morone saxatilis) larvae (Smircich et al. 2017).
The general impact of Zebra mussel grazing has been to strengthen littoral food webs and increase biomasses, while weakening the planktonic and deepwater benthic food webs, and decreasing biomasses there (Strayer et al. 2008; Strayer et al. 2011).
|Field and experimental studies indicate that predation by Blue Crabs (Callinectes sapidus) causes extensive mortality to Zebra Mussels in the Hudson River estuary (Boles and Lipcius 1997; Carlsson et al. 2011). Increased mortality has apparently stabilized the mussel population. However, it is not known if the Zebra Mussel has affected the abundance or distribution of Blue Crabs, or other predators in the Hudson River (Strayer et al. 2011).|
|Zebra Mussels have caused significant fouling to boats and docks in the Hudson (Strayer 2006).|
|Zebra Mussels have caused significant fouling to power plants and water treatment plants, in the Hudson River estuary. Fouling problems have required increased inspection and cleaning, and the use of biocides, such as chlorine, potassium permanganate, or polyquaternary ammonium compounds. The cost of these treatments probably varies from $100,000 to $1 million per year (Strayer 2006).|