New Publication: Increased Connectivity Between Freshwater and Marine Environments Strengthens Marine Ecosystems

In the Northeast United States, human activities such as river damming have reduced the degree to which freshwater and marine ecosystems are connected. For anadromous fish species such as the alewife, which live in saltwater and travel up rivers to spawn in freshwater, this diminished connectivity has led to dramatic decreases in abundance over the past several centuries and limits the current capacity for restoration. Because alewives and similar species serve as a vital food source for numerous marine predators, their decline has likely affected marine ecosystem functioning and species abundance, but such impacts have not previously been estimated.

To assess the potential benefits of increased linkages between freshwater and marine environments, Dr. Beatriz Dias and her colleagues first estimated historical alewife abundance from the year 1600, before any river dams were constructed and the species was free to travel upstream. This estimate was incorporated into an ecosystem model to assess historical abundance of a wide array of marine species. The researchers then compared the historical model’s results with those of a model depicting ecosystem conditions in the year 2000.

Dr. Dias and her co-authors found that restoring the abundance of alewives to historical levels in a few watersheds could lead to population increases for economically valuable predators such as cod and summer flounder along with dramatic rises in abundance for pelagic sharks, toothed whales, and several other species of conservation concern. These results demonstrate the key role of anadromous alewives and similar species as a forage base for marine predators. In a broader context, with oceans under threat from climate change and fisheries management shifting to an ecosystem approach, this work demonstrates the importance of a diverse forage fish base. Such research could inform policy discussions that weigh the benefits of restoring connectivity against the costs of dam removal.

Click here for the full paper.

Source: Dias, B.S., Frisk, M.G., and A. Jordaan (2019). Opening the tap: Increased riverine connectivity strengthens marine food web pathways. PLOS ONE. doi.org/10.1371/journal.pone.0217008.