Impact of Invasions on Water Quality in Marine and Freshwater Environments

Water quality of marine and freshwater environments, including brackish waters, can be highly impacted by the introduction, establishment, and spread of non-native species. Phytoplankton are among the most common arrivals, with the bloom-forming species, such as toxic freshwater cyanobacteria and marine dinoflagellates, being of particular concern. Their massive population increase may lead to water discolouration, reduced transparency, changes in nutrients cycling, events of anoxia, and release of potent toxins contaminating the food web and drinking water. Top-down control that regulates primary productivity is carried out by filter-feeding organisms. Bivalve mollusks are often the dominant filter feeders in many aquatic systems. The high filtration rates of some non-native bivalves may significantly increase the ecosystem filtration capacity, resulting in drastic changes of phytoplankton biomass and composition. Invasive bivalves also have a marked role removing other suspended particles, which result in increasing water clarity with subsequent growth of submerged vegetation. This apparent benefit may not be innocuous because changes in phytoplankton composition may lead to dominance of toxic algae species. Biomagnification of contaminants filtered from the water column, biofouling, and increase of sedimentation are among other detrimental effects associated with the increase of non-native bivalve populations. In this chapter, the main impacts on water quality raised by non-native phytoplankton and bivalve species are reviewed.