The rapid expansion of human transportation networks in the latter half of the 20th century yielded unprecedented economic and cultural exchange between nations but also ushered in a new era of human-mediated biological introductions. On land and in water, exotic species are reshaping the ecology of ecosystems around the world.
One such invader is the golden mussel (Limnoperna fortunei). The freshwater mollusk arrived in South America around 1990 from China and quickly spread up the Paraná and Uruguay rivers from the Río de la Plata estuary in Argentina. By 2017, it had reached densities exceeding 200,000 individuals per square meter in waterways across five countries. In less than 30 years, the mollusk became a major biofouling agent in industrial cooling systems and a benthic invader.
The mussel’s rapid invasion has transformed the aquatic environment, both biologically and physically. Biologically, the mollusk has reshaped species interactions thousands of years in the making. Physically, however, its impact is less clear. To better understand the environmental effects of the invasive species, Tokumon et al. studied how the mussel influences the sediments and geochemistry of the Río de la Plata estuary near Buenos Aires.
Over the course of 1 year, the researchers fed estuary water through 18 containers that contained water intake and outlet pipes. Half the units included mussels; half did not. The study monitored the changes in the accumulated sediment—concentrations of organic matter, nitrogen, and phosphorous—in the experimental units at monthly, biannual, and annual intervals.
The results indicate that golden mussels doubled the rate of sediment buildup and strongly enhanced the amount of organic matter and nitrogen in the sediment. The data largely align with previous findings on the effects of zebra mussels and other filter-feeding mollusks.
The mussels did not significantly alter phosphorous concentrations in the sediment, however. The broader body of research contains many conflicting conclusions on the effects of mollusks on sediment phosphorous levels, and this research contributes another data point to the still unresolved question.
Although the study’s conclusions should be viewed in the context of experimental conditions and carefully extrapolated to field conditions, they nevertheless offer new insights into how the golden mussel changes aquatic sediments and affects bottom-dwelling fauna. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1029/2018JG004399, 2018)
—Aaron Sidder, Freelance Writer