How does ballast water from oceangoing ships spread organisms between ports?

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kudzu — invasive species Kudzu (*Pueraria montana*) along a roadside in southern Virginia, U.S.

Oceangoing ships utilize ballast water to maintain stability and structural integrity when they are not fully loaded with cargo. When a vessel takes on water in one port to compensate for a lack of cargo, it inadvertently draws in local marine organisms, including plants, animals, and microorganisms.

When the ship reaches its destination and offloads its cargo, it must discharge this ballast water to maintain proper buoyancy and balance. This process results in the release of the transported organisms into a new, often foreign, environment. Because these species are frequently introduced into ecosystems where they lack natural predators or competitors, they can become invasive species, potentially disrupting local biodiversity and damaging the health of the receiving ecosystem.1