From barren deserts and dense forests, to oceans and mangroves, invasive species can pop up anywhere. Learning what they are, how they spread, and why they might be harmful to ecosystems can help us understand their impact on our planet.
What is an invasive species?
A species becomes invasive when it enters another habitat which wasn’t already home to it. This creates a clear distinction between native and non-native organisms, as a non-native species integrating into a new habitat is often considered invasive.
Invasive species can include fish, plants and crustaceans.
How do invasive species spread?
Research suggests that invasive species spread because of climate change. Additionally, harmful human activities such as overfishing and hunting can lead to some fish entering new habitats in search of food and shelter, causing invasive species to be introduced into a new environment.
An invasive species that can survive in their new environment can spread quickly since they often no longer face the same threats from their native habitat. In the absence of natural controls like diseases and predators, their population size can easily begin to outnumber that of other native species.
Why are non-native species harmful to ecosystems?
Non-native species can impact our ecosystems and surrounding aquatic life in several different ways.
One of the main concerns is that non-native species can cause a significant decline in the populations of native species, including animals, plants and other organisms. This is because the invasive species compete with natives for limited resources, potentially even altering the habitat. If native species decline while the number of invasive species increases, it can reduce biodiversity in the habitat and alter the food chain. Damage caused to the environment by invasive non-native species can lead to consequences for our food, lifestyle, economy and climate.
It’s important to make the distinction between non-native species and invasive species, since not all non-natives are harmful to the ecosystem. Some are deliberately or accidentally introduced to an environment and can have a positive impact on the environment. In reality, only around 1 in 10 non-native species will become invasive. A great example of a non-native species that isn’t harmful is tomato plants, which originally come from Ecuador and Peru but have been introduced to other countries such as the US and UK.
Examples of invasive fish species
Let us introduce you to some examples of invasive fish species, starting with one we have here at Blue Planet Aquarium…
Lionfish
All 12 species of lionfish are native to the Indo-Pacific Ocean, which is a tropical marine habitat. However, they’ve also spread to the West Atlantic Ocean, Caribbean Sea and Mediterranean Sea, making them an invasive species in these waters. Lionfish are considered to be invasive as they are skilled predators, they do not have a lot of natural predators and will predate on a lot of smaller fish and invertebrates. As such, fishermen and hobbyists alike are encouraged to actively search for and catch lionfish wherever they’re found swimming around beyond their native regions.
Walking catfish
Walking catfish (Clarias batrachus) originate from the warm waters in Southeast Asia, preferring ponds and canals. Humans introduced these extraordinary creatures into the waters around Florida in the early 1960s, quickly spreading along the coastline of North America. As natural predators of various creatures, including eggs or larvae of other fishes, small fishes, and several invertebrates, the walking catfish population in Florida threatens the biodiversity of numerous species.
As you might guess from their name, this species uses its special fins and tail to walk on dry land, essentially making it easy for them to wriggle from one body of water to another. This is thought to have helped them spread rapidly when introduced to the US!
Carps
Managing to simultaneously be classified as invasive, despite being vulnerable to extinction, the common carp (Cyprinus carpio) is a unique species.
Carp are native to Europe and eastern Asia, but they can be found in waters all over the world except the North and South poles and northern Asia. As bottom-dwelling fish, they feed by rummaging through the sediment at the bottom of a body of water, destroying the habitats of many other species and eating eggs of other fish.
Mosquitofish
First introduced as a way to control mosquito populations, since they primarily feed on mosquito larvae, mosquitofish (Gambusia affinis) are now classified as invasive in many regions, including Europe and Australia. The main reason for this is their aggressive behaviours towards native species when it comes to food, which also means they become less effective at controlling mosquitoes because they’re preying on other food sources.
Trout
Rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta) are some of the most invasive trout species in the world.
Brown trout, with their distinctive yellow and brown bodies with black and red spots along their side and back, are originally native to Europe, western Asia and North Africa, but they have now spread to almost everywhere in the world. This is largely due to them competing and winning against native trout species and other fish for food.
Meanwhile, rainbow trout have silver or green bodies lined with a distinct pink stripe that makes them easy to identify. This species is native to the western US, but as with the brown trout, it can now be found swimming around in almost all the waters around the planet, thanks to their unique adaptability. Easily overpowering other fish populations in streams, they tend to out-compete similar species and even drive some to extinction.
Check out our blog for more insights on what’s lurking in our oceans, rivers and seas. Better yet, why not visit Blue Planet Aquarium, where you can meet our exciting marine species? We’d love to welcome you soon!