Invasive Species and Algal Blooms

Algal blooms are not just caused by excessive nutrient addition to a body of water; there are many complex relationships at play. As discussed in earlier posts, climate change, addition of road salt, nutrients and poor storm-water management can lead to a Harmful Algal Bloom. Another contributing factor is invasive species; they can foster excessive algal growth. Invasive macrophyte species will push out native populations that produce allelochemicals that can inhibit phytoplankton blooms from forming. The invasive species that causes the most concern are mussels.

Invasive species are any non-native species that cause either environmental impacts or economic/recreational impacts to a body of water. The most common form of invasive species that can alter the aquatic ecosystem causing favorable conditions for an algal bloom to form are mussels; specifically zebra mussels and quagga mussels. Evidence has shown that invasive mussels can and will selectively feed on forms of algae that do not produce toxins. The mussels will “spit out” any form of algae that produces microcystis, as they focus on diatoms and other “healthier” forms of algae.

Invasive mussels don’t remove nutrients such as phosphorus from the water column; they only alter the way that the nutrients are cycled through the aquatic ecosystem. This results in lower amounts of phosphorus needed to trigger an algal bloom. The implications for nutrient reduction strategies and water quality protection in bodies of water with invasive species can be a challenge.