WASHINGTON — All the world’s seas are bedeviled by global warming, pollution and overfishing, but the Mediterranean and the 20-plus nations that ring it face another threat: A rising flood of invasive marine species flowing through the Suez Canal.

On Aug. 6, 2015, over the objections of environmentalists and the reservations of many economists, the canal’s latest expansion opened to shipping. The new 22-mile channel will double the canal’s capacity, allowing 97 ships to pass through each day. It also opens a wider path for invasive species from the Indian and Pacific Oceans to flood through the Red Sea into the Mediterranean.

Once they’re in, there’s no way to get them out, and the changes they bring are irreversible. Israeli scientists have identified more than 450 alien species of fish, invertebrates and algae that are not part of the Mediterranean’s natural ecosystem. Several pose public health hazards, while others threaten fisheries and tourism and denude underwater ecosystems, greatly reducing biodiversity.

Egyptian authorities say the $8.5 billion project will reduce bottlenecks and increase toll revenue from $5.3 billion to $13.2 billion a year by 2023. But these benefits come at the cost of continuing environmental degradation. “The recent doubling of the canal will decimate coastal ecosystems with dire implications for the regional economy and human health. We can’t continue to overlook this threat,” warns Dr. Bella Galil, a senior scientist at Israel’s National Institute of Oceanography.

It can take generations, she says, for an alien species to expand its range. The presence of Red Sea fish in the Levant Basin, for example, was not recorded until 1902, more than three decades after the canal first opened in 1869. Subsequent waves have followed major canal expansions in 1980 and in 2010. The eastern Mediterranean, mere miles from the canal’s mouth, has been hardest hit, and experts from Turkey, Cyprus, Greece, Israel and Lebanon say this invasion has drastically altered fisheries.

In the 1970s, according to Dr. Dor Edelist, a marine ecologist at the University of Haifa, invasive species constituted 21 percent of Israeli trawler catch; today, more than half are alien. In the first decade of this century, Israel’s Mediterranean fishery brought in $14 million to $26 million a year. Today, it’s about $16 million, of which $6 million to $10 million are invasive species. Some are edible, like the goldband goatfish, but it has replaced the native species, red mullet. Gone too are native food fish like European hake and porgies. Turkish and Lebanese fisheries report similar losses.

Putting a precise figure on the economic impact is difficult. Standard commercial fisheries statistics tell how much fish is caught and sold, but fishermen are notorious for underreporting their catch. And no one is tracking the economic loss from season to season as commercial species collapse or as environmental degradation reduces tourism.

Three alien species have been particularly destructive. Rabbit fish have devoured algal forests, leaving wide areas of bare rock and undermining the complex ecosystems of the Levant Basin.

A more recent arrival is the poisonous silverside puffer fish, native to the Indian and Pacific Oceans. Puffer fish eat 20 percent to 33 percent of fish caught on long-line hooks and often chew through a trawler’s nets, according to Aylin Ulman, a doctoral student at the University of Pavia, who studies Turkish fisheries. “Where gill nets used to last 15 years, puffer fish cause so much damage that nets have to be replaced in just a few months,” he says. Researchers say Greek fishermen face the same issues in the Aegean and off Crete. Among other prey, they devour such staple foods as squid, octopus and cuttlefish. Off the coast of Cyprus, the octopus catch has plummeted from 175 tons per year in 2001 to below 50 tons in 2009, according to the Sea Around Us, an environmental fisheries program run by the University of British Columbia.

Another voracious and painfully venomous predator, the nomad jellyfish, entered the Mediterranean in the 1970s. Now they form large swarms every summer, washing up on shores, endangering beachgoers and divers, blocking the water-intake pipes of power and desalinization plants. Swarms have reached the Straits of Sicily and are endangering Atlantic bluefin tuna eggs, threatening a fishery already on the verge of collapse.

Though we can’t remove invasive species, we do have the engineering expertise to stem the migration. The Panama Canal, which opened to shipping in 1914, offers an example of what might be accomplished. It operates a series of locks that function like sets of double doors, allowing ships to pass while making it more difficult for alien species to follow. Moreover, the fresh water of Gatun Lake, which forms a major part of the canal complex, provides a 21-mile barrier that impedes the migration of most saltwater species.

The Suez Canal once had its own salinity barrier, known as the Bitter Lakes. Previous expansions and agricultural wastewater dumped into the canal flushed it away, but recreating it could be cost-effective. Installing locks for the Suez Canal, located in a much simpler physical environment than the mountainous Panamanian region, should be easier and less costly than the $3.2 billion the Panama authorities expect to pay for modernized lock equipment.

Scientists and environmentalists have appealed to the European Commission to install locks and salinity barriers in the Suez Canal and have requested an environmental impact assessment. Despite Egypt’s assurances that the information would be provided by May, European Union officials say they have still not received a definitive report. But in discussions last October conducted by the United Nations Environment Program, the Egyptians reportedly said they would not sign an updated United Nations Mediterranean Action Plan unless language stating that invasive species are coming through the Suez Canal was removed. The MAP draft decision, with the language regarding the Suez Canal in brackets, goes to the Barcelona Convention for the Protection of the Mediterranean for review in February.

Observers say that Brussels doesn’t want to lean too hard on Egypt because President Abdel Fattah el-Sisi is cooperating in dealing with the refugee crisis. Many European Union member states with their own national interests in the Mediterranean see the Suez expansion as a sovereign decision by the Egyptian government and are loath to interfere.

But Egypt and its neighbors are losing sight of the big picture. For Egypt, with its large underemployed population, managing the fishing industry more wisely would employ more people and have greater long-term economic benefits than building expensive canal infrastructure that is vulnerable to a volatile global economy.

So, how can these competing interests be resolved? The problem may require new ideas and neutral leadership. In the mid-2000s, overfishing and environmental degradation was ruining fisheries off California. The Nature Conservancy bought up boats and licenses and leased these back to fishermen willing to employ more sustainable methods and use reporting software to help the NGO develop baseline data on the fishing stocks themselves. The result: Local fishermen are still fishing, and fish stocks are coming back. The program has been copied by several New England fisheries.

There’s surely a creative solution for the Mediterranean’s problems, and the place to start is by rebuilding salinity barriers in the Suez Canal. As we become more aware of the risks to our planet, we must remember that human beings, by nature, are not only competitive — we’re also cooperative.

D. Rachael Bishop