Dispersal of invasive species by ballast water

Introduction

An Invasive species, in other words, something that is non-native to a specific ecosystem, when introduced to a new area, may cause, economic and/or environmental harm to human health. Additionally, invasive species may be introduced to a given area in an unintentional manner. An example of this would be through the transfer of species via ballast waters. The transport of ballast water spreads an estimation of 7000 living species which range in their taxonomy, including Virus, Bacteria, Fungus, Plant, and Animals. These species discharged into new regions alter the ecological balance previously established.

Ballast Water

The purpose of ballast water is to provide transverse stability, improves propulsion, and maneuverability, and compensates for weight loss due to fuel and water consumption. Approximately 10 billion tons of ballast water is transported each year,  accounting for 90% of our world trade. Typically, ballast water discharge contains a variety of biological materials including non-native, invasive,  and exotic species that can cause extensive ecological and economic damage to aquatic ecosystems.

Figure 1. This image provides a visual demonstrating these cargo ships up taking and unloading the ballast water, to and from ports, transferring invasive species.

In doing so, these large ships withdraw up to 20 million gallons of water at their specific loading ports. Including the native species, both plant and animal, before disposing them at their next destination(s). Generally, one wouldn't think this would cause any harm. However, when these invasive species are unloaded, specific physical conditions like temperature and salinity affect how well these the foreign species not only survive but thrive to compete with the species native to that area. This competition is what causes stress within the ecosystems, throwing off ecological and environmental balance.

Invasive Species

Fresh Water Zebra Mussel

Zebra mussel are a Dreissena polymorpha species, that live in freshwater and are native to southern lakes in Russia and Ukraine. The zebra mussel has become an invasive widespread species carried by ballast water. Specifically, North America, Great Britain, Ireland, Italy, Spain, and Sweden are the areas where zebra mussels have become an invasive species. Zebra mussels tend to invaded native species habitats around them and successfully uptake oxygen and food; mostly affecting algae. The invasiveness of zebra mussels is disruptive to the ecosystem they surround. They have the tendency to damage boats, waterways, harbor, water treatments, and power plants, along with monotypic colonization.

The Sea Walnut

Figure 2. Mnemiopsis leidyi, commonly known as the Sea Walnut.

Mnemiopsis leidyi, commonly referred to as sea walnut, is a part of the tentaculate ctenophore species, and the class of comb jellies. Initially, this species is native along the Eastern coast of North and South America. Currently, Mnemiopsis leidyi has become invasive by transfer of ballast water to the Black Sea, Azov, Aegean and Marmara Seas, West coast of Sweden, Southern and Northern Baltic Sea. This carnivorous species feeds on zooplankton, crustaceans, fish eggs and larvae; some consume their own species that are smaller. Specifically, Mnemiopsis has become a problem for local fisheries because they have diminished the zooplankton population.

Green Crab

Carcinus maenas species goes by many names but is most commonly referred to as the green crab. The green crab is native to the Baltic Sea and the North-East Atlantic Ocean. This invasive species is widespread mostly carried out by ballast water, where it has colonized habitats off the shores of North and South America, Asia, and Australia. C. maenas is a voracious predator to many species such as worms, mollusks, oysters, and clams. The competitive and efficiency of this species outcompetes crabs and lobsters in their habitat for food. Specifically, the green crab disrupts eelgrass beds, which are homes for a variety of fish. For aquaculture and fishing industries, this species poses a threat due to their predation for mollusks along with harming eels when they get caught in traps.