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The Panama Canal joins the Pacific and Atlantic, making it a critical route for global maritime trade — but this interoceanic link also increases the risk of unintended introductions of marine species to new waters. 

The Panama Canal’s recent expansion has raised concerns a bout its new capacity to facilitate the movement of marine species. With more direct routes and increased water flow, understanding how this expansion may affect aquatic biodiversity is important for both ecological health and local livelihoods.

An international team of researchers — from the Leibniz Institute of Freshwater Ecology and Inland Fisheries, Freie Universität Berlin, Smithsonian Tropical Research Institute, and Harvard — analyzed fish community data from Gatun Lake, a central freshwater body in the canal system, both before (2013–2016) and after (2019–2023) the canal’s expansion. 

The team investigated the sizes of fish populations, species composition, and the origins of introduced species to determine whether the expansion altered the ecosystem and increased the likelihood of species movement between the Pacific and Atlantic Oceans. This long-term dataset allowed scientists to examine the ecological impact of the infrastructural changes on the connectivity between ocean basins. 

Findings

Following the expansion of the canal, the fish community became more abundant and active, and its composition shifted. 

Before expansion, the canal was mostly inhabited by introduced freshwater species (57%), introduced marine species (26%), and local freshwater species (17%). After expansion, introduced marine species became dominant, making up 76% of the catch, while introduced freshwater species dropped to 13% and local freshwater species to 11%. 

In addition, large marine predators have dominated the lake’s ecosystem after the canal’s expansion, signaling a fundamental reorganization of the food web in the area. 

While most introduced marine species in the area originate from the Atlantic Ocean, four out of the five Pacific-origin fish species were detected only after the canal’s expansion. This suggests that the expanded canal has increased movement from the Pacific Ocean, raising concerns about the two-way interoceanic travel of species. 

Ecological Impacts

The dominance of large marine predators poses serious ecological risks. Top predator introductions are associated with the loss of local fish species, bottom-dwelling invertebrates, and zooplankton — which can set off a chain reaction in the food web that causes phytoplankton to grow out of control, potentially harming water quality and oxygen levels. 

Moreover, the evolving fish community affects local fishing practices, as artisanal fishers must adapt to new species and altered food webs. 

For scientists, this rapidly changing environment offers a unique natural laboratory to study how marine species adapt to freshwater systems, offering insights into evolution under rapid environmental change. 

the full study
“New Fish Migrations into the Panama Canal Increase Likelihood of Interoceanic Invasions in the Americas” in Current Biology 

more on healthy ecosystems

Mason Ibrahim is the communication fellow for North Carolina Sea Grant’s award-winning Hook, Line & Science series, which published an earlier version of this story. Visit HookLineScience.com.