Challenge 7: Arresting the Alien Invasion: Combating Invasive Species

## THE PROBLEM

Invasive species can spread quickly once introduced into a new ecosystem. Surveillance and detection remain key barriers to preventing their spread into new regions and water systems. Once established in a new ecosystem, invasive species often disrupt finely balanced ecosystems because they are free from the competition or predation that exists in co-evolved systems. For example, species like the lionfish have begun to disrupt food chains in many areas, preying on valuable species and critical members of the ecosystem while multiplying due to the lack of natural predators.

## THE CHALLENGE

This challenge seeks new globally scalable systems, technologies, or financial innovations that aid the monitoring, prevention, and systematic removal of invasive species in ocean ecosystems.

This challenge focuses on:

1. Designing rapid, low-cost, immediate surveillance tools that can detect individual organisms in novel habitats and within carriers for such invasive species.

2. Creating novel technologies to prevent the introduction of invasive species at all scales (including microorganisms).

3. Developing innovations that could remove 95% of an invasive species in a novel habitat within five years, bringing the ecosystem back to pre- invasion baselines.

## PROBLEM STATEMENT

Globalization and increased international trade have progressively removed the common and natural barriers to alien species introduction into ocean ecosystems, resulting
in the loss of biodiversity and the homogenization of habitats. These sudden introductions brought about by the rapidity of global trade as well as the growing market for exotic aquarium species can lead to massive changes in the ecology of coastal and ocean ecosystems. Alien invasive species may compete with local species for limited supplies of food and habitat. They may serve as novel predators or introduce foreign diseases, driving native species locally extinct. The introduction of an alien invasive species to a coastal or ocean ecosystem can completely disrupt food chains, transform habitats, and drive down the abundance and health of keystone ecosystem species. Such invasive species may range from new apex predators, like lionfish, to invasive plants, to novel pathogens. Examples include the Chinese mitten crab, European green crab, Cladoceran water flea, zebra mussels, lionfish, and the North American comb jelly.

Invasive species may be introduced though novel connections between previously closed natural barriers (e.g., the Panama Canal, the Suez Canal) or through movement across traditionally natural barriers. Shipping carries 90% of internationally traded goods, and it is a significant conduit for invasive species. Many invasive species are spread through the ballast water of massive cargo ships along trade routes and then through natural waterways. As a result, many harbors around the world now share remarkably similar— and low biodiversity—ecosystems.

The zebra mussel, now one of the most common freshwater shellfish globally, was accidentally introduced to U.S. waterways where it quickly out- competed endemic species.

International trade in live marine organisms has also led to the expansion of invasive species. The spread of personal salt-water aquariums stocked with exotic species has increased demand for charismatic species around the world, like the lionfish, and inadvertently, contributed to their release into novel ecosystems where they no longer have predators to keep their populations in check. After the highly voracious and fecund lionfish was introduced off the coast of Florida, it quickly expanded its range and abundance to the entire eastern United States, the Gulf of Mexico, and the Caribbean Sea within the span of 15—20 years. In the process, it has severely depleted juveniles of grouper and snapper and has taken up a dynamic position at the top of the food chain with few, if any, natural predators for healthy lionfish across the entire eastern seaboard.

Aquariums can also inadvertently harbor microorganisms—like algae—that can have a dramatic impact on local ecosystems. “Killer algae” (Caulerpa taxifolia), a species native to the Indian and Pacific oceans was released from aquariums in Europe and has become a massively destructive force throughout the Mediterranean, altering the structure of ecosystems throughout the sea. In California, where killer algae also became a problem, a large-scale campaign of poisoning the invasive species was successful in eradicating it from most habitats.

EMERGING SOLUTIONS

To date, the majority of solutions to marine invasive species have focused on either preventing their invasion by treating the source, or on eliminating the species once they have invaded.

**Prevention:** As ballast water is a major source of invasive species, innovations have focused on treating it. These include using damaging properties of light (UV radiation), filtration systems, oxidation, and chlorination. Unfortunately, no ballast water treatment method can completely eliminate the risk of introducing exotic species. Alternative solutions include changing fundamental hull designs to allow for continuous flow of water through the hull as ballast, or eliminating the use of ballast water altogether.

**Surveillance:** Advances in the efficacy and costs of molecular biology have enabled better detection and surveillance of invasions without having to isolate the targeted organism. This approach, termed Environmental DNA (eDNA), analyzes nuclear or mitochondrial DNA that is released from an organism into the environment. Sources of eDNA include secreted feces, mucous, and gametes; shed skin and hair; and carcasses. eDNA has allowed for breakthroughs in monitoring invasive species because it can detect species abundance at low densities, including upon an initial invasion by larvae or seeds. Early detection decreases both the costs of control and the impact on ecosystems.

**Eradication:** Eradication once a species has invaded is much harder than preventing the invasion. Biocontrol is the regulation of a pest species through the introduction of a natural predator. It has been proposed as a tool for controlling invasive species, however, it has had unintended consequences in terrestrial systems. Biocontrol proposals for marine systems include viral or microbial biocontrol of algal blooms, predatory control of ctenophores (comb jellies), parasitic regulation of the European Green crab, and introduction of sea slugs and plant hoppers to control green algae and salt marsh cord grass. The challenge of biocontrol is to guarantee host specificity—that the species being introduced will not prey on other endemic species instead of the one it is intended to control.

Biocontrol isn’t restricted to living animals anymore. The Queensland University of Technology developed an autonomous star-fish killing robot, which seeks out crown-of-thorns starfish through a computerized imaging system, and then gives them a lethal injection. Although the crown of thorn starfish is not an invasive species in Australia, the decline of its predators coupled with increased organic material flowing into the ocean from terrestrial sources has led to its massive overpopulation and the subsequent destruction of its ecosystem. This process is not dissimilar to the way invasive species often harm native ecosystems, providing a glimpse into a possible technological solution for other habitats.

Synthetic biology offers another set of potential solutions: the ability to edit genomes and encode lethal genetic instructions that could be turned on or off (kill-switch genes) as has been done with the mosquito, Aedes aegypti, which is responsible for Dengue Fever and Chikungunya.

**Changing Market Demand:** Rather than directly addressing the number of species, we may seek to increase the demand for those species. We can increase financial incentives for the eradication of certain species by creating markets, providing incentives and bounties, and encouraging recreational harvest. For example, throughout the Caribbean a concerted effort was made to create a high-end market for lionfish.