Observed Dispersal of Invasive Yellow Flag Iris (Iris pseudacorus) through a Saline Marine Environment and Growth in a Novel Substrate, Shell Hash

Invasive in North America, Iris pseudacorus is commonly considered a freshwater species; however, I. pseudacorus can tolerate some saltwater, and is observed in brackish coastal habitats such as estuaries and marshes. Despite this tolerance, saltwater depresses I. pseudacorus reproduction, growth, survival, and dispersal ability. This raises the question of whether I. pseudacorus can spread through a marine environment and establish away from sources of freshwater. This study reports the observation of 104 established juvenile I. pseudacorus individuals in coastal habitat on two islands in southern British Columbia, Canada. Two islands that are devoid of aboveground freshwater sources such as streams, rivers, or lakes that connect to marine habitats. Individuals were also observed growing in a novel substrate, shell hash (fragments of bivalve and gastropod shells that accumulate in areas of low hydrological energy). To the best of our knowledge, this is the first confirmed case of I. pseudacorus growing in a high salinity (30 PSU) shell hash environment. Despite the need for more study, this observation suggests that a broader range of coastal habitat may be susceptible for invasion by I. pseudacorus than previously thought.