A Living Plague

Illustrated by: Helen Xiu

Off the coast of Florida, a slow alien invasion is in progress. Native to the South Pacific, the lionfish now gobbling up the reef is more familiar to most as an aquarium dweller. Indeed, the most likely source of the invasion is unwanted pets released into the ocean [2]. In humans, its venomous spines can cause intense pain and in some cases, paralysis and respiratory distress. Its lack of natural predators and voracious appetite devastates both ecologically and commercially important fish populations. In the warm waters of the Bahamas, it has gobbled up between 65-95 percent of native reef fish in just 30 years [3]. The proposed solution? Eat them. Lionfish are increasingly in demand in local restaurants, encouraging fishermen to hunt them down. However, as more diners find an appetite for the prickly predator, conservationists also may have to contend with the possibility that they will become popular enough to be overfished in their native waters as well [2]. In many ways, the lionfish is emblematic of the damage invasive species can have on native environments, species, and subsequent impacts on human health. 

Though lionfish are one of the flashiest invasive species, its impact on humans is for now mostly limited to run-ins with commercial fishermen and unwary swimmers. Other species pose a more systemic threat by damaging crops, injuring people and livestock, and uprooting entire communities. Plants, harmless in their native ranges, can reshape entire ecosystems. The prickly pear cactus, introduced to Kenya as an ornamental plant by European colonizers, has been overtaking the fragile rangelands that cattle herders and their animals depend upon. Animals who attempt to feed on the plant ingest thorns that catch in their stomach lining which cause them to eventually die. Even grazing on other plants nearby can result in livestock being blinded by thorns. As a result, the herders are forced off of their lands and lose access to the medicinal native plants that have been choked out by the cactus [4]. Other species like the fall armyworm (another North American species that has spread extensively across Africa) directly attack important crops like corn. The extensive insecticide use required to control it means farmers are forced to choose between a potentially tainted harvest or none at all [4]. The impact of invasive species such as these is felt most by developing nations that do not yet have the extensive infrastructure and technological and economic resources to control their spread. In the U.S, control of invasive species costs the nation $120 billion annually [5].

While the prickly pear cactus and fall armyworm attack crops and livestock directly, other invasive species worsen the effects of climate change by reshaping habitats. For example, buffelgrass was originally introduced in the United States to provide forage for cattle and then to prevent soil erosion. However, it spread out of control and has overtaken much of the desert region of the American southwest [4]. The highly flammable grass has grown over the fire-resistant desert, contributing to the increasing incidence of major wildfires in the area. These resulting fires directly threaten human life and property and cause declining air quality. In places like South Africa, invasive trees like black wattle and cluster pines use five times more water than native trees and are taking an enormous toll on the nation’s water supplies [6]. In 2018, Cape Town nearly became the first major city to run out of water, forcing strict water usage restrictions. As climate change prolongs droughts and causes more wildfires, invasive species increase the damage. 

However, most media attention has been given to invasive species as vectors of disease. They have perhaps the most noticeable impact on human health, as increasing globalization means that epidemics can now cross oceans in a day. Invasive species arrive every day in ship ballasts and airplane holds, and the pathogens they carry with them hitch a ride as well. The Norway rat, or brown rat, is perhaps the most prolific invader, originating in northern China and spreading to every continent except Antarctica.It is not only a carrier of diseases like bubonic plague, typhus, Weil’s disease, toxoplasmosis and trichinosis, but also carries parasitic mites and fleas [5]. Other species like zebra mussels are hosts for roundworm, which humans pick up through eating improperly cooked fish or drinking roundworm infested water [3]. The most famous example in recent memory is the Asian Tiger mosquito, which carries Zika, chikungunya and dengue viruses. The warmer temperatures brought on by climate change have allowed it to flourish in its introduced environment [1]. Its range in the United States now extends as far north as the Great Lakes region, and outbreaks of diseases previously rarely found in the continental U.S have become more frequent. 

Invasive species clearly take a massive toll on human life, property and infrastructure. However, history is littered with misguided attempts to resolve these problems. In 1883, in an attempt to control the rat population that had accidentally been introduced to Hawaii, European plantation owners released mongoose into the island [2]. However, as mongoose are diurnal and rats are nocturnal, the mongoose instead devastated the islands’ native bird population. Today in Hawaii, conservationists are attempting to control the spread of the invasive strawberry guava tree by introducing the Brazilian scale, an insect that feeds exclusively on strawberry guava trees. The strawberry guava produces fruit at such a high rate that it outcompetes native trees, forming vast monocultures that drastically impact the watershed [2]. However, the strawberry guava is also grown as a crop and Hawaii residents worry about their own trees and fear that the insect meant to control it will create larger problems just as the mongoose did in 1883. As with the lionfish and other invasive species discussed, every proposed solution comes with its own set of risks. Additionally, many people are resistant to attempts to control species that are beneficial for humans in the short term like the strawberry guava tree or buffelgrass. Ultimately, conservationists must somehow walk the knife’s edge of controlling invasive species with a “do no harm” mentality. 

Edited by: Julia Bulova
Illustrated by: Helen Xiu

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