Research led by Natalie Mastick from the University of Washington reveals an increase in Anisakis nematodes in canned salmon, suggesting a recovering ecosystem linked to marine mammal population growth. The study utilized preserved salmon from 1979 to 2019, finding higher parasite prevalence in certain species, which reflects the impact of conservation efforts. While the rise of parasites indicates ecosystem health, it also raises concerns about infections in humans and potential threats to salmon populations, emphasizing the need for ongoing research into parasite dynamics.
The original version of this article first appeared on Spektrum.de*
Ecosystem Recovery: An Increase in Salmon Parasites
Wild-caught fish are often hosts to parasites, which is why in Europe, salmon undergoes a deep-freezing process for 24 hours to eliminate larvae present in its muscle tissue.
While it may seem unconventional, what can decades-old canned salmon reveal about the North Atlantic’s ecosystem? Surprisingly, the preserved parasitic worms found in these cans indicate that conservation efforts for marine mammals, such as seals and whales, are bearing fruit. A research team led by Natalie Mastick from the University of Washington in Seattle has discovered an uptick in nematodes of the genus Anisakis in the flesh of two canned salmon species. This increase may correlate with the rising populations of marine mammals in the Eastern Pacific, as detailed in their findings published in the journal ‘Ecology and Evolution’. These marine mammals serve as primary hosts for the Anisakis parasites, allowing them to reproduce within their bodies. Additionally, this study highlights a novel method for gathering previously elusive data regarding parasite population dynamics.
Read more: Dead worms discovered: Smoked salmon tested
The Significance of Parasites
Though often unseen, parasites play a vital role in ecosystem dynamics. Similar to apex predators, they act as ecosystem engineers, influencing population sizes, nutrient cycles, and interspecies relationships. Despite their immense significance, knowledge about parasites remains limited. Their small size and tendency to inhabit other organisms complicate research efforts. Anisakis worms, in particular, are fascinating as their lifecycle encompasses various ecosystem components. They primarily target endangered marine mammals and commercially valuable salmon, making understanding their population vital for both conservation efforts and the fishing industry.
Anisakis larvae dwell in aquatic environments and are consumed by small crustaceans or other invertebrates. When fish consume these crustaceans, they too become infected, leading to the formation of cysts in their muscle tissue. This process continues up the food chain, ultimately affecting marine mammals like seals and whales, where the worms reproduce and release new larvae into the water. Consequently, wild-caught fish, including salmon, can harbor these nematodes within their muscle tissue.
Understanding Ecosystem Health Through Nematodes
Nematodes serve as indicators for assessing the health of an ecosystem, provided there is ample data on their population trends over time. The research team, led by Mastick, discovered a unique archive: cans of salmon from 1979 to 2019, preserved by the Seafood Products Association in Seattle for quality control purposes. They examined four salmon species caught in the Northeast Pacific off Alaska: Chum salmon (Oncorhynchus keta), Coho salmon (Oncorhynchus kisutch), Pink salmon (Oncorhynchus gorbuscha), and Sockeye salmon (Oncorhynchus nerka). In half of the 178 cans inspected, the team identified Anisakis nematodes. Notably, the prevalence of these worms increased in Pink salmon and Chum salmon over the years, while remaining stable in the other species.
This rise in parasitic load is likely linked to the recovery of marine mammal populations following legal protections established in the USA in 1972. Similar trends have been observed in other fish species, such as cod in the Baltic Sea and Atlantic. The absence of increased parasites in two salmon species may be attributed to various factors, including alternative food sources. Climate change also poses a potential influence, as it could exacerbate parasite loads in certain scenarios.
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Balancing Perspectives on Increased Parasite Numbers
The research team emphasizes that the rise in parasite populations has both positive and negative implications. On one hand, these parasites signify a recovering ecosystem that was once heavily exploited. Conversely, an increase in parasites may lead to heightened risks of infections and allergic reactions in humans. Additionally, with salmon populations facing greater endangered status today, the increased parasite load could pose new threats to their survival. Ultimately, this study underscores the importance of gathering data on parasites—even from unconventional sources—as a means to gain valuable insights into the health of ecosystems.
*This article first appeared with our partner Spektrum