The Mediterranean Sea is among the world’s great environmental jewels. The sea is highly saline, almost entirely enclosed by land and contains immense biodiversity. Scientists have long worried that its health is imperiled. Swelling coastal populations and ship traffic have brought overfishing and pollution. Climate change threatens to roil the waters still further.

One threat that is now gaining particular attention: the arrival of invasive species. One of the Mediterranean’s few outlets is the 146-year-old Suez Canal, which links it to the Red Sea and the ocean beyond. This creates a vital shipping route between Europe and Asia. But scientists fear that an expansion of the canal could bring more invasive species to the Mediterranean’s fragile waters.

Last year, Egypt announced plans to quickly build 45 more miles of waterway — a parallel canal, in part — so that ships can pass through more quickly than they do now. With the existing canal, they often must wait because the channel is narrow — about 1,000 feet wide at its slimmest point.

Because of the Suez and its expansion, the Mediterranean Sea’s problem with invasive species is becoming “worse than anywhere else on earth,” said Bella Galil, a senior scientist with Israel’s National Institute of Oceanography.