Global agriculture, as with aquaculture, is dependent to a significant extent on alien species, as is the case for all major food crops and husbanded terrestrial animals. However, voluntary and or accidental introduction of alien species is thought to negatively impact local biodiversity.

Approximately 17% of the world's finfish production is based on species alien to their environment. Tilapia, native to Egypt’s Nile River, easily adapted across the globe and is now farmed in over 85 countries doubling during the past decade to about 3.7 million tons with Asia representing about three quarters of world tilapia production.

Farmed salmon represented less than 10% of the global supply 20 years ago; it now accounts for over 60% of the salmon market. Between 1990 and 2000, the Chilean salmon farming industry grew 10 times while overall world production doubled. This performance is remarkable considering that commercial salmon farming in Chile started only a little more than 20 years ago. Unlike many other exporting countries – Norway, Canada, the UK and USA – salmon is not a species native to Chile, which currently ranks as the second largest exporter trailing only Norway.

The Pacific oyster was introduced to Northwest America from Japan in the 1920s and has grown into a $72 million industry. The Pacific oyster was then introduced to France in the 1970s with 562 tons of adult oysters from Canada and 5 billion spat brought in from Japan. By 2000 this alien shellfish represented 95% the country’s harvest amounting to 180,000 tons per annum. France in now the top producer and consumer of oysters in Europe and 130,000 tons are the Pacific oyster compared to only 1,500 tons of the native oyster. Moreover, the Pacific oyster is cultivated all along the French coast and 80% of the crops is produced from "alien" now naturalized spat.

The above remarkable stories validate immigration, adaptation, and proliferation of a foreign species for benefiting the economy of many nations. After decades of debates ecologists are increasingly classifying alien species as “naturalized or endemic”.

Invasion of Alien Species

Species invasions have occurred for as long as life populated the seas and there are now about 2.2 million species in the ocean. Invading species are particularly successful in disturbed habitats, especially those altered by human activities and climate change. Thus, these invaders have colonized human-altered environments having unprecedented and complex ecological tolerances that they have adapted to and which the native species could not.

Traditional ecologists and environmentalists are instigating a jihad against introduced species fearing "invasive species" as aggressive outsiders causing a holocaust among natives. In reality, the diversity and spontaneity of new “immigrant” biological communities mirror a modern transformative society. Indeed, the same processes that have galvanized globalization of the world economy – unfettered trade and travel among nations - have also caused the globalization of the environment.

In the progressive camp, Dr. Mark Davis a renowned biologist at Macalester College opines: “There is no evidence that even a single long term resident species has been driven to extinction, or even extirpated within a single U.S. state, because of competition from an introduced plant species”. Yet the spurious threat of extinction persists as one of the chief reasons given for trying to prevent the introduction of alien species.

Also in the progressive camp, Dr. Tomás Carlo, an assistant professor of biology at Penn State University whose research is published in the journal of “Diversity and Distributions”, logically articulates this viewpoint: "The fundamental goal is to return a natural area to its original, pristine state, with the native species occupying the dominant position in the community. But the problem is that humans already have changed most native communities beyond recognition, and many native species are now rare. Invasive species could fill niches in degraded ecosystems and help restore native biodiversity in an inexpensive and self-organized way that requires little or no human intervention. Nature is in a constant state of flux, always shifting and readjusting as new relationships form between species, and not all of these relationships are bad just because they are novel or created by humans. We need to be more careful about shooting first and asking questions later -- assuming that introduced species are inherently harmful. We should be asking: are we responding to real threats to nature or to our cultural perception and scientific bias?"

Exotic species receive unwarranted attention and create unnecessary worry. However, Dr. Dov Sax, an ecologist at Brown University and Dr. Steven Gaines, a marine biologist at the University of California, Santa Barbara, and several other researchers argue that attitudes about exotic species are too simplistic. While some invasions are indeed devastating, they often do not set off extinctions. They can even spur the evolution of new diversity. “I hate the ‘exotics are evil’ bit, because it’s so unscientific,” Dr. Sax said.

Dr. Sax and Dr. Gaines have analyzed the rise of exotic species on island chains and found that invasive plants have become naturalized at a steady pace over the last two centuries, with no sign of slowing down. In fact, the total diversity of these islands has doubled. For example, there are more naturalized invasive plant species in New Zealand than native species and they claim that the New Zealand invasion has not led to a mass extinction of native plants. The number of documented extinctions of native New Zealand plant species is a grand total of three.

Dr. James Brown a researcher at the University of New Mexico concurs with this theory. Whenever he visits a river where exotic fish have been introduced, “I ask, ‘Have you seen any extinctions of the natives?’ The first response you get is, ‘Not yet,’ as if the extinction of the natives is an inevitable consequence. There’s this article of faith that the net effect is negative.” Dr. Brown does not think that faith is warranted. In Hawaii, for example, 40 new species of freshwater fish have become established, and the 5 native species are still present. Dr. Brown and his colleagues acknowledge that invasive species can push native species out of much of their original habitat. But they argue that native species are not becoming extinct, because they compete better than the invasive species in certain refuges.

Could it be that whether the impacts of introduced species are positive or negative? Good or bad is a subjective value judgment rather than an objective scientific finding. “It’s not that this is all good or all bad, and I’m not sure science should be the arbiter,” Dr. Brown said. “Placing values on these things is the job of society as a whole.”

Aquatic Homogenization

Biological homogenization is the dominant process shaping the future global biosphere. As global transportation becomes faster and more frequent, it is inevitable that biotic intermixing will increase. Unique local biotas will become extinct only to be replaced by already widespread biotas that can tolerate human activities and climate change. This process is affecting all aspects of our world: language, economies, and ecosystems alike.

Emerging evidence shows that most species are declining because of human activities and climate change “losers” are being replaced by a much smaller number of expanding species that thrive in human-altered environments, the “winners”. The ultimate outcome is the loss of uniqueness and the growth of uniformity. The oceans are witnessing a broad and complete reorganization of species distributions and marine communities are becoming increasingly homogenized as a result.

There are few if any marine, coastal, or inland water systems that have not been impacted by aquatic aliens. At least 70 alien species have been found in every estuary that has been surveyed in the continental United States. San Francisco Bay is one of the most invaded bodies of water and one of the best studied. A new aquatic species becomes established every 14 days and there are now over 230 foreign species in the bay. They are introduced through ballast water, hitchhiking on ship fouling, and intentional transplants.

The construction of canals can remove dispersal barriers allowing species to cross between water systems that may have been isolated for millions of years. The opening of the Suez Canal introduced 250 new fish species into the Mediterranean Sea from the Red Sea. Consider: only a single extinction resulted.

The existential exigencies of climate change, deglobalization, changing demographics, and inevitable wars causing famine and malnutrition require a rethinking of this maligned topic. Consider that the number of people globally affected by hunger rose to as many as 828 million in 2021 - 46 million people more from a year earlier, and 150 million more from 2019 according to the United Nations.