Invasive Marine Species

Carl Safina surfacing with a netted lionfish

Invasive species are animals and plants that hitchhike or ride along to places where they are not normally found.  In their new homes, invasive species can sometimes create big problems for native species and ecosystems.

The main source of marine invasive species is the global shipping industry, specifically through ballast water.  Species can also be introduced through aquaculture, bait and bait-related packaging, and the live seafood and aquarium trade.

Ballast water remains the primary route for invasive species introduction.  When a cargo or large passenger ship is empty, hundreds of gallons of water – and any marine species in that water — are sucked into tanks in the ships’ hull to stabilize and level the boat.  This is ballast water.

As the ship moves to another port, the marine organisms in the ballast water get a free ride to a new marine environment–halfway across the world sometimes.  When the ballast water is pumped out to load the cargo, any surviving creatures pour into the new waters.

Freed from their predators and diseases, their numbers sometimes explode, and they overrun their new habitats.

Zebra mussels, known for clogging up waterworks throughout the Great Lakes, and lionfish, a Pacific and Indian-ocean species that somehow reached the Caribbean in the early 1990s, are two examples of invasive species.

Lionfish eat large numbers of native reef fish and have few predators in their new territory.  They’re abundant now and spreading all along the southeast US coast and have been found as far north as Rhode Island. Check out Carl Safina’s lionfish blogs (4 parts) and the Saving the Ocean episode on PBS TV covering the lionfish invasion.

Various groups are taking action to suppress the wide variety of invaders and reduce the chances of new arrivals.

3 things you can do to help stop invasive species:

1. Research proposed actions that would regulate ballast water.
2. Don’t release aquarium fish into local waters.
3. Volunteer in local campaigns to remove invasive species.

Other great ways you can make a difference.


Scourge of the Lionfish – Saving the Ocean, PBS TV
Marine Invasive Species – Int’l Union for the Conservation of Nature
Zebra Mussel – US Department of Agriculture
The Invasive Lionfish – USGS, You Tube
Taking on the Invaders – Nature Conservancy
Gulf of Maine Invasive Species Report – Gulf of
Ballast Water Management – US Coast Guard
Filleting the Lionfish – NOAA
Invasive Species – American Museum of Nat History, You Tube