INVASIVE SPECIES! Guide to Identify Impostor Creatures While Diving

INVASIVE SPECIES! Guide to Identify Impostor Creatures While Diving

The invaders are here. Yes they are.

But this time they don’t wear horned helmets like the mighty Vikings, not even a black pirate patch that allows you to identify them as the evil invader to be fought.

In the animal world, invaders arrive quietly but steadily, make themselves comfy in the invaded habitat and kick out local species that usually are less aggressive. These are the invasive species, officially recognized as Invasive Alien Species or IAS for acronym lovers.

They cause so much damage that releasing IAS into the wild in, for example, Florida, can result in a $1,000 fine or a year in jail.

But how do they arrive in the first place?

Sarah Speight

Most of the cases are linked to human activities, the invasive species furtively hops (or swims or sneaks) into a human transport and gets a free ride to a new habitat to be conquered! These are the ‘hitch-hikers’ or ‘stowaways’!

The yellow and purple Japanese starfish is an evil hitch-hiker. From Japanese waters they decided they wanted to go south and sneaked in ships ballast water. A few years later there were up to 1,100 young seastars per m³ in Derwent. And they might be pretty but they roam the sea floor eating everything in their path, from fish to other starfish.

Others are plainly man’s fault. Or we could say ignorance’s fault.

We human love infrastructures, and make connecting paths everywhere. The Atlantic is separated from the Pacific by land and I want to cross with my boat? No problem, let’s build a 77 km (48-mile) canal.  These artificial connections between areas that were previously separated facilitate human displacements, but also animal ones.

The jellyfish reef: Can you imagine a coastline with 25 jellyfish per square meter? That is how some Mediterranean shores can look like when thousands of Red Sea jellyfish arrive. The gelatinous critter entered the Mediterranean through the Suez Canal and made itself at home.

People also intentionally introduce invasive species. Men have been tasting oysters all over the world and taking with them the best ones. And oysters go one step further than threatening the local marine life, they carry pathogens and parasites to the new habitats! That’s why it is important to have a strict control in aquaculture and minimize risks.

Here we still get to blame the Vikings! Interestingly archaeological records show that the Vikings brought home with them a species of large North American clam, probably for food.

Spotted! And now how do we get rid of them?

The ocean is the environment a diver knows best, and sometimes is the divers who realize that something is wrong with the species in a dive.

It was divers who in 1999 spotted unfamiliar bivalves in a Northern Australian marina, which turned out to be Black Striped Mussels, the first recorded alien marine pest in Australian tropical waters.

Vagabond Shutterbug

Divers are usually involved in marine IAS eradicating efforts. One of the most impressive stories is how divers successfully eradicated and surveyed the Black Striped Mussels.

Divers had to be protected from crocodiles by armed crocodile spotters! And this elimination is one of the very few successes in the world.

Know your enemies

Let’s take the US as an example. There are an estimated 500 alien marine species only within its coastal waters. Around 200 of these are found in San Francisco Bay alone.

If divers are able to identify them, we are one step forward.

All divers have a favorite spot, you just need a colorful guide of your area so you know the species that should be there and you will be able to spot the impostor right away!

Do you have any invasive species in your area? What are you doing to fight them? Tell us in a comment below!


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