A risk-based decision model and risk assessment of invasive mussels

Ecological risks and economical impacts of zebra mussels (Dreissena polymorpha) include alterations in the transfer of energy and cycling of materials in aquatic systems, increased accumulation of contaminants in aquatic food chains, clogging of water intakes, and damage to related infrastructure. A risk-based decision model was developed to assess the likelihood of zebra mussel invasion and establishment throughout the St. Croix Basin. The risk-based decision model CASM_ZM is a version of the comprehensive aquatic systems model (CASM) and that was modified to simulate the growth, reproduction, and spatial distribution of zebra mussels. As a risk management tool, the model simulates the population dynamical complexity of zebra mussel populations, as well as their impacts on phytoplankton, zooplankton, benthic invertebrates, fish and natural mussel populations. The CASM_ZM is based in part on a set of zebra mussel's physical–chemical habitat requirements such as calcium concentration (17 mg/L), total hardness (57.5 mg/L), conductivity (62 μS/cm), dissolved oxygen concentration (6 mg/L), salinity (7 PSU), pH (6.8 and 9.4), Secchi disk depths (75 and 205 cm), and water temperatures for growth (14 °C) and reproduction (30 °C). The CASM_ZM also includes a bioenergetics framework that describes the growth of zebra mussels and their trophic impacts on aquatic food webs. The CASM_ZM can be used to forecast the risk of successful dreissenid invasions and assess the associated impacts of invasive mussels on food web dynamics of previously uninfested aquatic systems throughout the St. Croix Basin.