comment A new wave of marine fsh invasions through the Panama and Suez canals Recent engineered expansions of the Panama and Suez canals have accelerated the introduction of non-native marine fshes and other organisms between their adjacent waters. Measures to prevent further invasions through canals should be incorporated into global shipping policies, as well as through local eforts. Gustavo A. Castellanos-Galindo, D. Ross Robertson and Mark E. Torchin he world is inexorably connected by respectively. Canal expansion projects Tables 5 and 6), and to more ship traffic and shipping corridors that are expected have been fundamental to the economies lock usage. The new locks have a different to be increasingly used in coming and competitiveness of both countries. design to the original locks and may T1,2 years as world maritime trade grows Recent expansion of the Suez Canal, which serve as more effective fish ladders. They by an estimated 3.5% per year3. Canals finished in 2015, included the construction include large water-saving basins designed have transformed shipping routes since of an additional, 35-km long channel. to retain and recirculate some of the lockage at least the sixth century bc. Alongside Expansion of the Panama Canal, completed water. They also bypass Miraflores Lake, their role in global economies, they have in 2016, included the construction of new which separates two sets of original locks on established connections between ocean larger locks that allow the transit of large the Pacific side and restricts organisms from basins and marine biotas that were separated NeoPanamax vessels. moving into Lake Gatun (Fig. 1). for millions of years4. Two of these, the Previous predictions8–10 that these Panama and Suez canals, are major shipping expansions would lead to an increase in Future scenarios for shipping and fsh corridors that are considered hotspots for NNS introductions are proving correct. invasions at both canals biological invasions5. Eight new Lessepsian fish species have The Panama and Suez canals are important The Suez Canal (opened in 1869) is a passed through the Suez Canal into the corridors for world trade; their use shortens marine, sea-level canal and the Panama Mediterranean since 2015 (Supplementary shipping distances and reduces CO2 and Canal (opened in 1914) is a freshwater Table 1), representing an 8% increase in sulfur emissions. When they were originally canal approximately 29 m above sea species number and a twofold increase built, little was known or thought about level and accessed by locks at each end. in the average annual detection rate11 the environmental consequences of their Previously, both canals incorporated compared to the period 1869–2015. In construction. However, the considerable constraints to biotic exchange between the Panama, we have documented an increase body of knowledge now available on the marine biogeographic regions that they in marine species just four years after the risk of NNS introductions can inform connect. The Bitter Lakes of the Suez Canal expansion. Over the century prior to the future environmental risk assessments. historically served as hypersaline barriers 2016 expansion, 18 marine fish species Changes in shipping routes due to ongoing that limited movement of marine species, were recorded inside Lake Gatun. Between shifts in trade and climate change may alter but the progressive enlargement of the 2019 and 2020, using the same standardized usage patterns of both canals15. Tariffs, canal has diluted these lakes. This enhanced gillnet sampling methods at the same sites transit times and capacity are all factors habitability of the canal has facilitated the as in ref. 12, we recorded 11 previously that influence competition between the establishment in the Mediterranean Sea of unreported marine fishes contributing to a two canals and contribute to the rationale over 400 marine non-native species (NNS), total of 29 now known to occur in the lake for canal expansions. Climate change may including more than 100 species of marine (Fig. 1, Supplementary Table 2). Further, the also alter the pace of NNS introductions fishes, from the Red Sea6 (called Lessepsian abundance of some marine species (jacks, through the canals: the ‘tropicalization’ of migration7). Within the Panama Canal, snooks, marine mojarras and ladyfish) has the Mediterranean is expected to provide Lake Gatun, a large artificial freshwater greatly increased in parts of the lake, almost conditions more suitable for establishment lake enclosed by the locks, has formed a entirely replacing the freshwater fish present of Lessepsian migrants from the Red Sea16. barrier preventing most marine species shortly before 201612 (Supplementary Similarly, recurring drought in Panama in the Caribbean Sea and Eastern Pacific Tables 3 and 4). is expected to reduce freshwater input to from moving to the opposite ocean because Higher abundances of marine fish in Lake Gatun and potentially increase salinity they do not tolerate freshwater. However, Lake Gatun increase the risk of such species and the risk of marine NNS transiting the the Panama Canal has also recently been invading in both directions to the opposite canal. There are hundreds of native species expanded, allowing more movement of ocean. Proxies such as salinity-tolerant of marine fishes on the Pacific and Atlantic marine fishes into Lake Gatun. diatom species in lake sediments reveal a coasts of Panama that are known to tolerate long-term increase in salinity of the lake13. brackish water (Supplementary Note 1), and Recent expansions of the Panama and However, the recent changes in the lake even a slightly brackish canal could allow Suez canals fish community may be due to more recent some to cross to the opposite ocean. Activity through the Panama and Suez increases in salinity14, as observed from Now is the time to incorporate these canals account for 10% of the gross domestic comparison of data collected before and economic, social and environmental product (GDP) of Panama and Egypt, after the canal expansion (Supplementary scenarios with scientific knowledge about NATURE ECOLOGY & EVOLUTION | www.nature.com/natecolevol comment Suez Canal Panama Canal New channel Old channel Pacific side Atlantic side Old New Old Miraflores 30 Lake 100 Old 20 75 50 New 10 Number of fish species 25 Number of fish species 0 0 1869–2014 2015–2020 1914–2016 2016–2020 Pre- versus post-expansion Pre- versus post-expansion Fig. 1 | Major, recent expansion works in the Suez and Panama canals, and the increase in non-native marine fish species in the Mediterranean Sea (Suez) and Lake Gatun (Panama). Note the dual channels of the Suez Canal, large recirculation (water-saving) basins beside the new Panama locks, and old Pacific locks with Miraflores Lake in between. For fish data, see Supplementary Tables 1 and 2. Credit: Suez Canal images adapted from NASA Earth Observatory images by Jesse Allen, using Landsat data from the US Geological Survey (USGS) Global Visualization Viewer (GloVis); Panama Canal images contain modified Copernicus data (2018) processed by Sentinel Hub. the risk posed by NNS. The introduction assessments. Further, through the 2017 for most marine species, and that can of the Indo–Pacific lionfish into the Ballast Water Management Convention, the be restored. Past actions to limit NNS in Greater Caribbean17 serves as an example International Maritime Organization (IMO; the Great Lakes of North America could of possible ecosystem consequences of the UN agency responsible for sustainable provide alternative approaches. For example, the introduction of NNS through the two shipping) has implemented guidelines and environmental DNA24 and sonar detection25 canals. The lionfish became a Lessepsian obligations to reduce the spread of NNS could be used for studying movements of migrant invading the Mediterranean in via ship ballast water, sediment and hull NNS in the canals, and acoustic, electric around 2012, and enhanced access to that biofouling20,21. We suggest that canals should and hydrological fish deterrents26,27 could sea may have facilitated its ongoing rapid be explicitly included in these legal agendas. be tested. Combined with the appropriate population expansion there18. The lionfish, Considering the slow pace of international decision-support tools28, these measures which has severely impacted Caribbean policy making, an additional way to manage could enable effective management of NNS. reefs through its consumption of native NNS in canals could be to engage key actors Finally, the socio–ecological consequences fishes and crustaceans17, is an ecologically of the shipping industry that are willing to of NNS introduced via the two canals are resilient species that can tolerate low salinity address this issue in the quest for a more poorly understood. In the Mediterranean, conditions. Its presence near the Atlantic sustainable ocean economy22. The UN NNS have replaced native species in several entrance to the Panama Canal poses a Decade of Ocean Science for Sustainable fisheries and blooms of unwanted NNS, such risk for it invading the Eastern Pacific if Development (2021–2030) provides the ideal as jellyfish, impact tourism6,29. Any measure increased salinification of Lake Gatun framework to accelerate the science and to manage NNS in canals should include all continues. management needed to control NNS in canals stakeholders and acknowledge all potential The risks of transporting NNS are being and more broadly in the shipping industry.