Ballast water often leads to marine species being transferred to different marine environments, posing great risks in oceans. Specifically, five invasive species that have been seen disrupting marine environments are:

#1 Northern Pacific sea star (Asterias amurensis)

This species although is native to the coasts of northern China, Korea, Russia, and Japan, has been seen in the southern coasts of Australia. It is able to eat a wide range of other organisms and is a great challenge for Australia's waters, mostly because it consumes the eggs of the endangered handfish.

It can also live in a variety of temperatures and water salinities and can carry up to 20 million eggs, giving it the potential to spread far and wide.

#2 Cholera (Vibrio cholera): 

This species can rapidly spread through ballast water, being a crucial threat to humans if ingested via drinking water or seafood.

It’s not only larger organisms that are causing problems. Bacteria such as Vibrio cholera can quickly spread via ballast water, posing a serious threat to humans if ingested via drinking water or seafood. It is reported that a cholera outbreak caused by ballast water discharge led to 12,000 deaths in Latin America.

#3 Zebra mussels (Dreissena polymorpha):

The zebra mussels spreads either through larvae in ballast water, or by attaching itself to vessels and other solid objects. This species is able to severely affect water treatment plants by clogging pipes in the water.

Moreover, when it is attached to vessels, it increases ship resistance, heavily affecting fuel costs and emissions. If not treated rightly, it can increase corrosion of steel and concrete, making equipment and infrastructure more susceptible to failure.

#4 Comb jelly (Mnemiopsis leidyi):

Although it moves slowly, it has managed to invade numerous non-native environments, such as the Black Sea, Caspian Sea, and the Baltic and North Seas.

It has a negative impact on the shipping industry, as it is known for eating ten times its body weight.

#5 European green crab (Carcinus maenas):

This green crab (also known as a shore crab) originally came from Europe. It is adaptable and has now been seen in Southern Australia, South America, South Africa, and coastlines in the United States.

In light of the marine pollution and disruption resulting from invasive species, amendments to an international treaty aiming to prevent the spread of potentially invasive species in ships' ballast water entered into force on 13 October 2019.

The amendments set out an implementation schedule to make sure that ships manage their ballast water to meet a specified standard (D-2 standard). They also make mandatory the Code for Approval of Ballast Water Management Systems, which establishes how ballast water management systems used to achieve the D-2 standard have to be assessed and approved.