Sources/Usage: Public Domain. View Media Details

Benthic invertebrates play vital roles in estuarine ecosystems, converting organic material into prey for larger consumers and aerating sediments with their movements. But like other groups of estuarine organisms, they were excluded from former marshlands by diking and land use conversion over the last ~100 years. Dike removal is one way of restoring tidal marshes, yet the response of benthic invertebrates has been little studied.

In the study, researchers characterized invertebrate community variation across the Nisqually River Delta over four years following the 2009 Brown’s Farm restoration, relating invertebrate response to environmental conditions such as elevation, salinity, and sediment grain size and organic content.

By regularly collecting benthic invertebrate samples in restoring marsh, previously restored marsh, undisturbed reference marsh, and adjacent tidal flats, the researchers found that marine species including crustaceans, polychaete worms, and bivalves immediately colonized areas recently restored to tidal inundation, and population size grew exponentially thereafter for several of those species. Community composition and diversity recovered completely, and density and biomass were approaching recovery three years later.

The researchers also found that just offshore from the dike line, invertebrates declined one year after dike removal but then rebounded, indicating resilience to short-term disturbance. Environmental variables most associated with invertebrate community variation were elevation, salinity, and sediment grain size and organic content.

These results are relevant to assessing performance of and setting expectations for future tidal marsh restorations, with broad implications for the role of benthic invertebrates in the recovery of valued and sometimes endangered species such as birds, fish (e.g., Chinook salmon), and other wildlife in estuarine ecosystems.