General Impact
Musculista senhousia can dominate benthic communities and potentially exclude native species. It settles in aggregations and is therefore able to reach high densities. Unlike most mussels, M. senhousia lives entirely within the sediments, surrounded by a bag of byssal threads. At mussel densities of greater than 1500 m2, individual byssal bags coalesce to form a continuous mat or carpet on the sediment surface. The presence of these mats dramatically alters the natural benthic habitat, changing both the local physical environment and the resident macroinvertebrate assemblage. Although this can result in increased species richness and abundance of some species, mussel mats reduce the densities of many common native bivalves and the growth of nearby eelgrass (NIMPIS, 2002; Allen and Williams, 2003). Crooks (1999) found that the effects of M. senhousia appear to be scale dependent. At larger scales, surface-dwelling, suspension-feeding clams are competitively inhibited. At smaller scales, however, the mussel benefits a variety of biota.
M. senhousia deposits large amounts of organic matter in the sediment, which possibly results in the accumulation of toxic metabolites such as sulfide, which can have adverse effects on seagrass growth (Morton, 1974; Ito and Kajihara, 1981; in Reusch and Williams, 1998).
Location Specific Impacts:Sacca di Goro Lagoon (Italy) 
Competition: Musculista senhousia probably competes with suspension feeders, such as Ficopomatus enigmaticus and Mytilaster minimus, in the Sacca di Goro Lagoon (Italy) (Mistri, 2003; Mistri et al. 2004).
Economic/Livelihoods: Large areas of the Sacca di Goro and the Gulf of Olbia are dedicated to the culture of Manila and carpet-shell clams (Ruditapes philippinarum and Tapes decussatus), respectively, the presence of mats of M. senhousia has been claimed to reduce clam growth and survival, however, experiments conducted by Mistri (2004) found that the presence of the mussel had no effect on either clam species.
Modification of natural benthic communities: Some changes in the macrobenthic community have been observed since the arrival of Musculista senhousia in Sacca di Goro (Italy), suggesting a positive effect on species diversity, especially detritivores and herbivores such as Neanthes succinea, Streblospio shrubolii and Microdeutopus gryllotalpa (Mistri, 2003, Mistri et al. 2004). Gulf of Olbia (Italy)
Economic/Livelihoods: Large areas of the Sacca di Goro and the Gulf of Olbia are dedicated to the culture of Manila and carpet-shell clams (Ruditapes philippinarum and Tapes decussatus), respectively, the presence of mats of M. senhousia has been claimed to reduce clam growth and survival, however, experiments conducted by Mistri (2004) found that the presence of the mussel had no effect on either clam species. Auckland Harbour (New Zealand)
Reduction in native biodiversity: Creese et al. (1997) found significantly fewer macrofaunal invertebrates under mussel mats in the Tamaki Estuary, New Zealand, compared to areas of beach which did not have mussels. Infaunal bivalves were the most adversely affected by M. senhousia, showing an 8-fold decrease in abundance within mats. Tamaki Estuary (New Zealand)
Reduction in native biodiversity: Creese et al. (1997) found significantly fewer macrofaunal invertebrates under mussel mats in Tamaki Estuary, New Zealand, compared to areas of beach which did not have mussels. Infaunal bivalves were the most adversely affected by M. senhousia, showing an 8-fold decrease in abundance within mats. New Zealand
Reduction in native biodiversity: Creese et al. (1997) found significantly fewer macrofaunal invertebrates under mussel mats in Tamaki Estuary, New Zealand, compared to areas of beach which did not have mussels. Infaunal bivalves were the most adversely affected by M. senhousia, showing an 8-fold decrease in abundance within mats. United States (USA)
Reduction in native biodiversity: Musculista senhousia may have adverse impacts on Zostera marina beds which are patchy and sparse. This may have implications for Z. marina conservation management, as many beds are already seriously degraded and limited in southern California (Reusch and Williams, 1998). Mission Bay (San Diego) (United States (USA))
Competition: Eelgrass (Zostera marina) is conditionally threatened by Musculista senhousia, which interferes with its vegetative growth when at high densities. At present, M. senhousia presence is negatively correlated with eelgrass (Zostera marina) beds, with the mussels growth rates decreasing with increasing eelgrass patch size. However, increasingly frequent phytoplankton blooms resulting from coastal development and eutrophication could result in an increased threat to eelgrass, as increasing phytoplankton availability to M. senhousia enhances mussel survival and growth, therefore combining the negative effects of phytoplankton blooms on eelgrass populations with increased survival of M. senhousia (Allen and Williams, 2003).
Reduction in native biodiversity: Musculista senhousia mats supported higher densities of the tanaid (Leptochelia dubia) and the gastropod Barleeia subtenuis at Mission Bay, California, USA (Crooks, 1998), while Crooks and Khim (1999) found that M. denhousia mats enhanced populations of the snail Barleeia subtenuis, nemerteans and amphipods, while the polychaete Pseudopolydora paucibranchiata and planktonic developers were inhibited. Crooks (2001) showed that M. senhousia negatively affects the survivorship and growth of the clams Chione undatella and C. fluctifraga. California (United States (USA))
Reduction in native biodiversity: Musculista senhousia may have adverse impacts on Zostera marina beds which are patchy and sparse. This may have implications for Z. marina conservation management, as many beds are already seriously degraded and limited in southern California (Reusch and Williams, 1998).
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