A red lionfish with a scuba diver. Who is the worst ocean invasive species?
An invasive species, the red lionfish. Photo by Giles Harvey / Pixabay

A big cause of environmental change is the invasion of non-native species. Here we look at the top 5 worst ocean invasive species that are currently blighting our oceans.

Invasive species can be moved around the world by latching onto ships or being carried by ballast water. They can be transported accidentally with other cargo. Or used as pets then discarded into the wild. Or be released deliberately into different habitats for commercial purposes.

The problem with this is that these species’ may not have a natural predator and may thrive in a new environment. While this could be a good thing, often it is not. As the species can consume and take over the local habitat, this drives local species’ out or destroys them completely.

Check out our Top 10 Most Dangerous Marine Animals.

Worst Ocean Invasive Species

Northern Pacific Seastar

Scientific Name: Asterias amurensis
This seastar was originally found around Japan, South Korea, and Russia. They have now made the long journey down to the southern coasts of Australia. While its natural habitat is a chilly 7-10°C, it has developed a tolerance and now thrives in warm temperatures of up to 25°C.

The seastar is a ‘voracious feeder‘ and will consume gastropod molluscs, barnacles, scallops, crabs, crustaceans, worms, sea urchins, sea squirts and more. And has even been discovered eating other seastars, dead fish and fish waste if no other food is available! Crikey!

Why is the Northern Pacific Seastar one of the worst ocean invasive species?

Because it eats everything! It is a ‘mariculture pest’ that has affected marine farms and cost millions of dollars in marine farming.

Green Crab

Scientific Name: Arcinus maenas
This green crab originated from Europe and was commercially fished for years. However, due to its wide tolerance in habitat, these crabs have thrived and pose a serious threat to delicate ecosystems around the world.

Green crabs can tolerate temperatures ranging from 0 to 33°C, salinities from 4 to 54, starvation for up to 3 months, and air exposure in damp burrows for up to 10 days, giving them the upper edge against native crabs.

Why is the Green Crab one of the worst ocean invasive species?

Because it is a predator that has been credited as single-handedly (or single-claw!) bringing down the soft-shell industries in several regions of Canada and the United States!


Scientific Name: Pterois
There’s no denying that lionfish are impressive looking creatures. They are also very popular with photographing divers and snorkelers. However, their lack of natural predators has made this quite the invasive species when introduced into new habitats.

The lionfish is a predator native to the Indo-Pacific region. But globally they became very popular in the aquarium trade. This has led them to successfully invade the areas around the United States, the Bahamas, and the Caribbean where they destroy the local eco-systems due to a lack of predators.

Read More: Is a Lionfish Poisonous or Venomous?

Why are Lionfish one of the worst ocean invasive species?

A study in the Bahamas found that a single lionfish per reef ‘reduced young juvenile fish populations by 79 percent in only a five-week period.’ So the baby fish don’t stand a chance!

Crown of Thorns Starfish

Scientific Name: Acanthaster planci
Known as a ‘corallivore,’ these impressive-looking starfish feast on coral which has devastating consequences on our marine eco-system.

A single crown-of-thorns starfish can graze on ten square metres a year of coral and an individual female can produce up to 60 million eggs per year. You do the math here!

Why is the Crown of Thorns starfish one of the worst ocean invasive species?

These starfish, along with storm damage, coral diseases, and temperature-related stresses, are recorded as the most damaging to coral reefs. Apart from our next invasive species…


Scientific Name: Homo sapiens
Ah, the worst invasive species for last! These guys have spread all over the globe. Humans breed slowly but due to their extensive numbers, the total population is consistently growing.

Humans have cleared land, purposely or inadvertently caused floral and fauna extinction, consumed natural resources, and have claimed the ocean too. Their negative impact on our oceans include; mass fishing, general pollution, sunscreen use, kicking of coral, marine life poaching and more.

Read More: Our Top Picks for the Best Reef-Safe Sunscreens

Why are humans the worst ocean invasive species?

Because we actually introduced all of the invasive species included in this list, around the world!

Let us know if you think there are worst ocean invasive species that should be included in this list. Do you think humans take the top spot?