There are not really different “oceans” or “seas” but one interconnected ocean that covers 71% of our planet. Despite being one huge body of water, there are a variety of natural barriers (for example, created by temperature differences, currents, and physical structures) that have created varying marine habitats with life that has evolved in “isolation” from others. Accordingly, each of these can have completely different species of plants, animals, and microorganisms making up the ecosystem.
As humans have moved throughout the ocean, some species have moved with them; introducing plants, animals, and microorganisms into areas far from their natural range. This can happen intentionally, but usually is unintentional. Regardless, species that have been moved into a new area where they don’t naturally occur are called introduced or alien species.
Some of these marine immigrants perish in the unknown habitat. Some of them live out their life without affecting their new home. But some of them thrive in the new area without the old checks and balances (like predators or disease); these are invasive species. Invasive species have had an enormous impact on marine biodiversity, ecosystems, and sometimes human economy and health.
The number of introduced species has doubled in the last 50 years worldwide; in 2019 there were 1,711 known. Not all of these will go on to cause damage in their new environment; in 2019, the IUCN listed 59 marine invasive species.
Invasive species thrive in their new environment because they don’t have natural predators or natural deterrents such as disease to keep the population under control. This can allow the population to grow very quickly.
Invasive species can alter an ecosystem in a variety of ways:
In the United States alone, $1.4 trillion in annual damages and 42% of threatened and endangered species can be attributed to invasive species.
Here are some examples to help understand the impact invasive species can have:
Green Crab (Carcinus maenas)
This European and North African native has established populations on both coasts of North America, South America, Australia, South Africa, and Japan. They first appeared on the east coast of North America in the 1800’s, presumably as ship ballast. Since that time they have had an enormous impact on shellfish in every area where they live as one small crab will eat three-dozen small mussels every day.
Killer Algae (Caulerpa taxifolia)
This green seaweed is native to the Indian and Pacific Oceans. It was bred for the aquarium trade throughout the world. Likely through people emptying their aquariums into local waterways, killer algae has spread to the west coast of the United States (where it has since been eradicated), Japan, Australia, and widely throughout the Mediterranean Sea. This algae forms dense meadows that crowd out native algae and seagrasses. It produces toxins that herbivorous fish cannot eat so it not only replaces local plantlife, but local fish can’t find food.
Sea Walnut (Mnemiopsis leidyi)
This comb jelly (stingless jellyfish-like animal) is native to the east coast of North and South America. However, in 1982 it was discovered in the Black Sea where, without any predators, it decimated local fish populations (anchovies, scad, and sprat). Not only did the sea walnut feast on zooplankton, an important food source of local fish, but it also fed on the eggs and larvae of those same fish. In less than 15 years, sea walnuts accounted for 90% of the biomass in the Black Sea! Sea Walnuts have since been discovered in the Caspian, Mediterranean, Baltic, and North Seas.
Zebra Mussel (Dreissena polymorpha)
This fresh and brackish water mollusk was originally native to the Capsian and Black Sea lagoons and rivers. In 1998, it was discovered in the Great Lakes of North America and has since spread throughout rivers and lakes in eastern and central North America from Canada to Mexico. These little mollusks have proven so prolific in their new environment that not only have they starved out native mollusk species, but their sheer numbers interfere with human structures such as intake pipes and ship rudders! From 1989-2000, between US$ 750 million and US $1 billion was spent dealing with invasive zebra mussels.
Lionfish (Pterois volitans & Pterois miles)
Originally from the Indian and Pacific Ocean regions, lionfish were introduced by the aquarium trade into the Gulf of Mexico and have since spread throughout the Western Atlantic and Caribbean. Not only do lionfish have no natural predators in this region and have very high breeding rates (one female can spawn over 2 million eggs each year!) but they are temperature and depth resistant so they adapt to new environments easily . Dense lionfish populations can consume up to 460,000 reef fish per acre per year!
Chinese Mitten Crab (Eriocheir sinensis)
An interesting example of a non-threatening introduced species becoming an invasive species is the Chinese Mitten Crab in the UK. This crab was found off the UK shores for 60 years without noticeable signs of being invasive. But, in the 1990’s, after several dry summers changed the river flow, the crabs were able to settle, and reproduce in large numbers. Chinese mitten crabs now travel long distances upstream, feeding on native species and burrowing into river banks leading to bank collapse.
There are a number of ways in which humans help other species to travel from their native waters to different parts of the world. Some are easier to control than others.
Most marine invasive species are transported via ship ballast. Large ships fill their tanks with seawater to counterbalance the weight of their cargo. They fill the tanks in their loading port (up to 20 million gallons/75 million liters) and release the water, along with whatever is in it, at their destination. An estimated 7000 species are carried daily in ballast from schools of fish to microscopic organisms. Annually over 10 billion tons of ballast water is transported by ships around the world each year.
It isn’t only through ship ballast that invasive species hitch a ride. Biofouling is the accumulation of microorganisms, plants, algae, or small animals on underwater surfaces. Ships provide plenty of underwater surface for invasive species to attach. Hulls, anchors, and other marine equipment can unintentionally bring invasive species with them.
Many people enjoy having exotic marine life in home aquariums. However, sometimes the plant or animal grows too big, reproduces too prolifically, or becomes aggressive to others in the aquarium. Regardless of the reason, well-meaning aquarium owners can choose to release their marine pets “back” into the ocean. Unfortunately, where the pet owner lives, may be very far from where the plant or animal should live, thus potentially introducing an invasive species.
Many aquaculture farms raise non-native species for human or animal consumption. Sometimes, due to overspill into surrounding waters, or an escape, these animals can enter the local habitat. Similarly, eggs can be released by farmed animals and can survive and multiply in the surrounding environment. This can lead not only to invasive species, but interbreeding between farmed and wild strains.
Sea Temperature Rise
As sea temperatures continue to rise, organisms will migrate into cooler waters and non-native habitats. This creates competition for limited resources as invasive species enter new ecosystems.
There are millions of tons of plastics and other trash floating in ocean currents. Because they are buoyant and slow to degrade, plastics offer marine organisms the opportunity to travel for long periods of time over great distances. After the 2011 tsunami in Japan, 289 Japanese marine organisms travelled to western North America over a period of five years on pieces of plastic debris!
Many of the things you can do to help with other ocean issues, such as reducing your carbon footprint, reducing plastic pollution and helping to clean up on land and in water can generally help with the spread of invasive species as well.
There are also specific things you can do:
If you fish:
If you have a boat:
If you are a scuba diver:
Invasive species are a difficult focus for conservation organizations as they vary regionally, and methods of mitigation are customized based on a number of factors and with a number of players including local and national governments.
One organization working to educate and make a difference with invasive lionfish in the Gulf of Mexico is REEF, Reef Environmental Education Foundation.
Please look online to see if there are marine invasive species in your area and if there are organizations who need your support!
Ballast Water Regulations, International Maritime Organization
In 2017, the International Maritime Organization introduced new regulations requiring ships to exchange or treat their ballast water before entering coastal areas. Ship captains can prevent many invasive species from invading new areas simply by flushing and refilling ballast tanks with water from the open ocean before they arrive in port (in deep water far from the coast, animals flushed out of the ship’s tanks are not likely to survive). Alternatively, they can use on-board treatment technology to treat the ballast water before its release in ports. This has been ratified by countries representing 70% of all global maritime shipping.
Green Crabs, Nova Scotia
Faced with an exploding population of invasive green crabs, park authorities in Nova Scotia, Canada, got creative! Since 2015, Parks Canada has run an ecotourism initiative taking tourists to haul traps and remove crabs while learning about the ecosystem and invasive species.
With a goal not of eliminating the invasive crabs but keeping their population at levels that allow other species to thrive, they are also working with fishers and scientists to find alternate uses for the crabs: from lobster bait to using their shells to create more eco-friendly biopolymers or using them as fertilizer. Having a scientific or commercial market for the invasive species creates an economic incentive to remove it!
Invasive Species Program, Reef Environmental Education Foundation
Invasive lionfish are destroying huge numbers of coral reef dwellers in the Gulf of Mexico and the Caribbean. REEF (Reef Environmental Education Foundation) has a database for sightings of lionfish in these waters and they work with government agencies throughout the region to develop lionfish response plans. They train divers and snorkelers on safe and effective collection and run Lionfish fishing derbies to help reduce the population. In 2020, 1321 lionfish were caught in one weekend. Overall, the REEF derbies have removed more than 23,000 invasive lionfish since 2009.
Gregory Ruiz, Smithsonian Environmental Research Center
Gregory Ruiz, a Senior Research Scientist at the Smithsonian Environmental Research Center, has studied the environmental impact of marine invasive species for over 30 years. His work resulted in a federal reporting system, improved enforcement policies, and environmentally safer shipboard management practices. Ruiz’s analysis found that voluntary reporting achieved only 40% compliance with regulations; which prompted significant fines that resulted in 90% compliance one year later. His work has reduced the accidental importation of invasive species into the US and has had an impact worldwide through the International Maritime Organization.