Understanding Marine Invasive Species for Invasive Species Awareness Week

Published on 2/25/25

Written by Jessica Colla

Invasive Species Awareness Week (ISAW) is an annual event dedicated to raising awareness about the profound impacts of invasive species on ecosystems worldwide. Established in 2010, ISAW highlights the importance of preventing the introduction and managing the spread of these species to protect biodiversity, economies, and human health.

This blog dives into the stories of marine invaders, their impacts, and what we can do to combat their spread!

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As a professional marine biologist, I’ve had firsthand experience with invasive species management. One of the most memorable projects I participated in was conducting lionfish population surveys and removal efforts in the Bahamas. These striking fish, though beautiful, wreak havoc on coral reef ecosystems. They prey on vulnerable native species and outcompete them for resources like food and shelter.

Witnessing the resilience of these ecosystems when given a chance to recover from invasive species presence inspired my dedication to sharing knowledge about invasive species.

Crown of Thorns Seastar Population Management in Fiji

Performing a Lionfish Dissection in the Bahamas

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Understanding Marine Invasive Species

Marine invasive species are non-native organisms introduced into oceanic environments where they establish, proliferate, and cause harm to native ecosystems. These species often outcompete native organisms for resources, alter habitats, and disrupt ecological balances.

Location, Location, Location 

The impact of an invasive species often hinges on its location. Within its native range, an organism is typically harmless because predators, prey, and competitors have co-evolved alongside it, creating a balanced ecosystem.

For instance, lionfish in their Indo-Pacific habitat coexist with predators that keep their population in check and prey that have evolved defenses against their hunting strategies. However, when lionfish were introduced to the Atlantic Ocean, they found an environment devoid of natural predators, allowing them to proliferate unchecked. Native prey species in the Atlantic, unfamiliar with the lionfish's ambush predation tactics, became easy targets, leading to significant declines in biodiversity.

Introduced vs. Invasive Species

This imbalance highlights the critical distinction between an invasive species and an introduced species. While both are non-native, an introduced species may integrate into a new ecosystem without causing harm, such as many ornamental plants used in landscaping.

An invasive species, by contrast, disrupts its new environment, causing ecological or economic harm due to its ability to outcompete, predate, or reproduce at an extraordinary rate. Understanding this distinction is key to addressing the threats posed by invasive species and preventing the spread of those with the potential to wreak havoc on ecosystems.

Threats close to home

While invasive species are typically non-native, some native species can also become threats under certain conditions. These native pest species experience population booms due to changes in environmental factors such as habitat degradation, overfishing of their predators, or climate shifts.

A well-documented example is the Crown-of-Thorns Seastar (Acanthaster planci), also known as COTS, a coral-eating species native to the Indo-Pacific, including the Great Barrier Reef. When their natural predators decline and nutrient availability increases—often due to human activities like agricultural runoff—these seastars undergo explosive population growth, devastating coral reefs.

Though these organisms are part of their native ecosystems, their unsustainable growth can cause significant ecological damage, blurring the lines between natural population dynamics and human-induced environmental disruptions.

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Case Studies:

Lionfish (Pterois spp.)

Originating in the Indo-Pacific, lionfish have invaded the Western Atlantic, Gulf of Mexico, and Caribbean. They are voracious predators that consume over 50 known species of fish and invertebrates, leading to significant declines in native populations. Check out the Florida’s Fish & Wildlife Conservation Commission page for more information here!

On survey dives in the Bahamas, I saw the devastating effects firsthand—reefs that were once teeming with native herbivorous fish were eerily quiet, blanketed in algae due to the lionfish’s impact. In prime habitat, rocky outcrops with ample cover for ambushing prey, I regularly encountered dozens of lionfish in only a few square meters--an unnatural density for these species in their native waters.

Efforts to control their population outbreaks include organizing spearfishing derbies (like this one organized by Reef Environmental Education Foundation, also known as REEF) and “round-up” fishing events, promoting lionfish as an edible delicacy to enjoy on local restaurants, and developing traps specifically designed to target them. I’ve been lucky enough to eat many delicious lionfish tacos in my lifetime!

European Green Crab (Carcinus maenas)

Native to Europe, green crabs have invaded North American coastlines, Australia, and South Africa. They prey on native shellfish, including clams and young oysters, disrupting fisheries and damaging eelgrass beds.

Here in Washington state, you can report sightings of European Green Crab to the Washington Department of Fish & Wildlife. I had a great conversation with a department representative, who said they recently trapped and removed hundreds of green crabs from a single estuary—a stark reminder of their impact on local ecosystems. Learn more about EGC’s here!

Green Crabs are edible despite being a less marketable species. So … support invasive species eradication through culinary efforts like crab cakes!

Zebra Mussel (Dreissena polymorpha)

Zebra mussels, originally from the Caspian and Black Sea regions, have spread to the Great Lakes and other freshwater systems, attaching to boats and water infrastructure.

I once spoke with a dive operator on Lake Michigan who described scraping off bucketloads of mussels from their dock annually. Their filter-feeding alters water clarity and disrupts food webs, threatening native mussels. Public education campaigns and strict boat cleaning protocols are critical to their management.

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The Role of Human Activities in the Spread of Invasive Species

Human activity is the primary driver of invasive species translocation:

Ballast water discharge from ships is a major vector; vessels fill their tanks with water from one port and release it in another, often carrying microscopic larvae and other organisms. For example, the zebra mussel was introduced to North America through ballast water in the 1980s, leading to massive ecological and economic damage.

The aquarium trade also contributes significantly. Lionfish, now one of the most destructive invasive species in the Atlantic, were likely introduced through the release of unwanted pets into the wild. A dive shop in Florida once recounted how hobbyists used to release their lionfish into the ocean thinking it was an act of kindness, unaware of the catastrophic consequences.

Hull fouling is another major contributor, with marine organisms attaching to the bottoms of ships and hitching rides across the globe. During a fieldwork project in Australia, we examined invasive sea squirts that had traveled on the hulls of recreational boats, displacing native species and altering marine habitats.

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Ecological & Economic Impacts

Marine invasive species cause extensive ecological damage, often leading to biodiversity loss by outcompeting native species or preying on them directly. For example, the introduction of the Indo-Pacific lionfish to Atlantic reefs has decimated native fish populations crucial to reef health, such as grazing herbivores.

Beyond ecology, invasive species impose significant economic burdens. In the United States, invasive species cause an estimated $120 billion in damages annually, affecting industries such as fisheries, tourism, and infrastructure. The costs of controlling zebra mussels in the Great Lakes alone have reached tens of millions of dollars per year.

Ecosystem services are also disrupted. For instance, green crabs degrade eelgrass beds that provide essential habitat for fish and buffer coastlines against erosion. Such changes have cascading effects on local economies that rely on these services.

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Management & Prevention Strategies

Preventing the introduction of invasive species is far more cost-effective than managing established populations. Policies regulating ballast water discharge and hull cleaning have been implemented in many regions to reduce the spread of marine invaders. Early detection and rapid response (EDRR) systems are critical, as they allow for swift action to eradicate invasive species before they become established.

Community involvement is equally important. Invasive species awareness campaigns have empowered recreational boaters and aquarium owners to take action, such as cleaning equipment and avoiding the release of non-native species. During Invasive Species Awareness Week, citizen science programs often encourage individuals to report sightings of invasive species, providing valuable data for management efforts.

Here are some ways individuals can help support invasive species prevention and management:

1. Educate Yourself and Others

Understanding invasive species, their impacts, and how they spread is the first step to prevention. Share your knowledge with friends, family, and your community to raise awareness. Participate in events like Invasive Species Awareness Week to learn more and spread the word.

2. Clean, Drain, and Dry Recreational Equipment

If you boat, sail, kayak, fish, or dive, thoroughly clean your gear before moving it to a new location. Aquatic invasive species like zebra mussels and Eurasian milfoil can hitchhike on boats, paddles, and even wetsuits!

Clean: Remove visible mud, plants, and animals from all gear.

Drain: Empty all water from boats, live wells, and bilges.

Dry: Allow equipment to dry completely before using it in another water body.

3. Be Responsible with Pets and Plants

Avoid releasing aquarium pets, plants, or water into the wild. Non-native species, like the lionfish or invasive aquatic plants such as hydrilla, often originate from aquarium trade and releases.

Return unwanted pets to stores, shelters, or rehoming programs.

Dispose of aquarium plants responsibly by freezing or sealing them in a bag before discarding them.

4. Volunteer for Local Conservation Programs

Join community initiatives like invasive species removal projects, beach cleanups, or habitat restoration events. Many organizations, like local conservation groups or state wildlife agencies, organize invasive species control efforts such as green crab trapping or lionfish derbies.

5. Report Invasive Species Sightings

If you encounter a suspected invasive species, report it to local or national agencies. Early detection and rapid response (EDRR) can prevent the species from establishing and spreading. Many regions have hotlines or apps, such as iNaturalist or EDDMapS, to report sightings.

6. Follow Local Regulations

Abide by laws and guidelines designed to prevent the spread of invasive species, such as not transporting firewood to new areas or complying with ballast water discharge regulations. These rules are in place to protect local ecosystems and prevent accidental introductions.

7. Support Policies and Research

Advocate for and support policies aimed at controlling invasive species, such as funding for research, prevention programs, and rapid response initiatives. Consider donating to organizations working on invasive species management and eradication.

8. Participate in Citizen Science Projects

Get involved with citizen science programs focused on monitoring and managing invasive species. Projects like the Great Lakes Invaders Watch or Reef Check empower individuals to contribute data that helps researchers track the spread and impact of invasives.

9. Be a Responsible Traveler

When traveling, avoid transporting species unintentionally. Clean hiking boots, fishing gear, and luggage to prevent carrying seeds, insects, or other organisms to new areas. Avoid purchasing or transporting non-native plants, animals, or souvenirs that may introduce harmful species.

10. Promote Native Species

Opt for native plants in landscaping and gardening to reduce the risk of introducing potentially invasive species. Native species support local ecosystems, providing habitat and food for native wildlife. Seek advice from local extension offices or nurseries on native alternatives.

By taking these steps, individuals can play a significant role in preventing and managing invasive species, safeguarding ecosystems, and supporting biodiversity conservation.

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Conclusion

Marine invasive species pose significant threats to global biodiversity, economies, and human health. During Invasive Species Awareness Week, it is imperative to recognize the role of human activities in their spread and to engage in proactive measures to prevent and manage these invasions. Through collective efforts in policy implementation, public education, and scientific research, we can mitigate the impacts of invasive species and protect the health of our marine ecosystems for future generations.

For more information, check out the National Invasive Species Information Center, OR your own region’s invasive species website (here is an example from Washington’s Invasive Species Council) to find the most impactful invasive species near you, and what you can do to help!

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