When an exotic species enters a new ecosystem, the immediate assumption is often that it will negatively impact native species. However, reality is more complex, and new species don’t always bring harm. A good example of this is the introduction of an oriental shrimp, Palaemon macrodactylus, into the Guadalquivir River estuary in Spain. Although this exotic shrimp has gradually increased in number, its presence hasn’t necessarily been detrimental to the native white shrimp, Palaemon longirostris.

In fact, both species seem to coexist in the estuary thanks to some key physiological differences. The exotic P. macrodactylus can tolerate lower oxygen levels and thrive in brackish waters (waters that are partially salty and partially fresh), which are common in certain areas of the estuary. This unique tolerance allows P. macrodactylus to occupy inner parts of the estuary that P. longirostris previously underutilized, thus reducing direct competition.

So, while P. macrodactylus and P. longirostris may share similar diets, they manage to coexist because they occupy slightly different niches within the ecosystem. This example shows that, although the introduction of new species can sometimes lead to negative effects, it can also result in more complex ecological interactions, where exotic species find ways to fit into the environment without necessarily harming native species.

Reference: González-Ortegón, E., Cuesta, J. A., Pascual, E., & Drake, P. (2010). Assessment of the interaction between the white shrimp, Palaemon longirostris, and the exotic oriental shrimp, Palaemon macrodactylus, in a European estuary (SW Spain). Biological Invasions, 12, 1731-1745.