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Sample Sidebar Module

This is a sample module published to the sidebar_bottom position, using the -sidebar module class suffix. There is also a sidebar_top position below the search.
Ecosystem Impacts

Ecosystem Impacts

Invasive species are collectively known to have negative impacts on native biodiversity and ecosystem functioning (Sakai et al. 2001, Strayer 2010). NZMS are spread through ballast water in ships, on fishing and boating gear, through contaminated fisheries, and in the guts and on the bodies of migratory animals. The ecosystem impacts of NZMS are variable and often dependent on their density in the invaded region, which can be exceptionally high (Kerans et al. 2005, Neiman et al. 2013, Bennett et al. 2015). In the United States, the highest reported densities are around 500,000 snails m-2, such as in Polecat Creek, Wyoming (Richards 2002, Hall et al. 2003), nearing the globally highest recorded density of 800,000 snails m-2 in Lake Zurich, Switzerland (Dorgelo 1987). Comparatively, NZMS reach maximum density around 50,000 snails m-2 in their native range. 

Ecosystems under anthropogenic stress are more susceptible to invasive species colonization due to a lack of native species, niche availability, and weakened ecosystem resilience. As such, NZMS are particularly effective at colonizing impaired ecosystems and those in the early stages of ecological succession (Schreiber et al. 2003, Alonso and Castro-Diez 2008). 

While ongoing research around the world aims to better understand the impacts of NZMS in invaded ecosystems, there has been little research conducted in the Great Lakes region. The Great Lakes New Zealand Mud Snail Collaborative is working to understand the consequences of NZMS on the Great Lakes and its tributaries.

Effects on Benthic Macroinvertebrate Communities 
NZMS compete with native macroinvertebrate (aquatic insect) populations for resources, such as food and habitat. Through these interactions, NZMS have the potential to alter native macroinvertebrate assemblages (Kerans et al. 2005). However, impacts appear to be dependent on NZMS density and other environmental factors and are species-specific; interactions range from interference competition to potential facilitation, and the presence of NZMS often leads to diminished biodiversity of native macroinvertebrates (Cada 2004, Kerans et al. 2005, Riley et al. 2008, Kerans et al. 2010, McKenzie et al. 2013, Spyra et al. 2015, Hansen et al. 2016). Of particular interest is their interactions with native snails (Riley et al. 2008), which perform important functions in water bodies, due to concerns of NZMS potentially outcompeting them. As the preferred food source of NZMS is periphyton – the nutritious microbial conglomerations that live on submerged surfaces – they likely have the greatest effect on other macroinvertebrate consumers of periphyton, such as snails (Levri et al. 2017). NZMS alter the composition and abundance of periphyton communities in their invaded ecosystems, resulting in potentially negative interactions with species that have similar niches (Cada 2004, Bennet et al. 2014). In some cases, native snails have been shown to adapt their diets to reduce their reliance on periphyton in the presence of NZMS (Larson and Ross-Black 2016).  

Effects on Nutrient Cycling and Trophic Level Processes
As primary consumers, snails provide an important link in aquatic ecosystems between primary producers (plants and algae) and higher consumers. The presence of NZMS is suspected to impair trophic level energy transfer and, subsequently, numerous other processes. NZMS are adaptive primary consumers that can utilize several food sources, such as detritus and periphyton, and fix carbon and nitrogen at high rates. Hall et al. (2003) found that NZMS consumed 65-92% of the primary production and excreted 65% of the ammonium needed by microbes and plants in three studied streams in the Greater Yellowstone area. As such, NZMS can dominate carbon and nitrogen fluxes in aquatic ecosystems in areas of high density. As is discussed in the Effects on Vertebrate Communities section below, NZMS often do not decompose in consumer digestive tracts. Therefore, NZMS represent a roadblock in the process of energy transfer throughout the food web, locking up stores of carbon and nutrients in their biomass and not passing this energy on to higher trophic levels. This becomes particularly concerning in areas where NZMS reach high densities and begin to dominate the macroinvertebrate community.

Effects on Vertebrate Communities
In invaded ecosystems, NZMS may alter the diet of benthivorous predators by dominating macroinvertebrate communities, an important food source for fish. NZMS often survive passage through the digestive tracts of fish predators, depending on the species (Fig. 1), due to the hardness of their shells and the aid of their operculum. As such, predators are provided little energy and nutritional value despite feeling full, even in their native range (McCarter 1986). Even when NZMS are effectively consumed, they are not efficiently assimilated – this leads to diminished body condition in fish whose diet they are a substantial part of (Vinson and Baker 2008). No studies to date have indicated positive prey selection for NZMS, likely due to the high cost to reward ratio posited by their shell hardness and small amount of soft tissues (Rakauskus et al. 2016, Butkus and Rakauskas 2020, Butkus and Višinskienė 2020). However, as NZMS populations increase, fish incorporate them into their diet at increasing rates either to compensate for diminishing numbers of native macroinvertebrates or through accidental ingestion (Vinson and Baker 2008). This poses significant concern over the effects of NZMS on native fish communities.