Handful of Species Key to Ecosystem Health, Study Finds
While conducting field research in the humid salt marshes of Sapelo Island, scientists Marc Hensel and Brian Silliman made an astonishing discovery: species type, not just quantity, is vital for maintaining healthy ecosystems. For decades, scientists believed that preserving the largest number of species was critical for ecosystem function, regardless of their genetic makeup. However, Hensel, a PhD student at the University of Massachusetts at Boston, and Silliman, Rachel Carson Associate Professor at Duke University, counter the old dogma in an article recently published in Proceedings of the National Academy of Sciences.
"It's quality, not just quantity," stated Hensel. "We need to preserve a wide variety of species."
By examining the relationships among three dominant consumer species (i.e., grazers and predators), Hensel and Silliamn found that it isn't just the number of total species, but the number of specific species that is crucial to upholding ecosystem performance. Working in the cordgrass (Spartina alterniflora) dominated salt marshes of Sapelo Island in the Southeastern U.S. state of Georgia, the researchers measured the effect of species loss on ecosystem performance. Salt marshes are seemingly simple ecosystems composed of a few extremely abundant and influential species.
The research team created eight different experimental plots that simulated the loss of three dominant groups: purple marsh crab (Sesarma reticulatum), marsh periwinkle snail (Litoraria irrorata), and fungi (Mycosphaerella species and Phaeospheria spartinicola). Each of the three evolutionarily distinct species plays a critical role in regulating marsh functions and maintaining habitat structure. Over a period of eight months, the researchers assessed the impact of the loss of these species on ecosystem functions by measuring the rates of grass growth, decomposition and filtration of tidal or storm water.
Hensel and Silliman found that although each species influenced just one or two specific ecosystem functions, the overall performance of marsh functions dropped considerably when one or more of the consumers were removed. Furthermore, the presence of very different groups was essential for providing a realistic assessment of marsh functions, particularly the inclusion of fungal species.
Fungus is not only a dominant group in the Sapelo Island salt marsh, but microbes such as fungal spores are key components of the food web and considered fundamental underpinnings of ecosystem functions. Therefore, by including fungus, Hensel and Silliman gained a deeper, more complete understanding of the marsh ecosystem functions and services.
Salt marshes provide coastal communities with essential services such as buffering waves, filtering urban water runoff, and providing nursery habitat for commercially valuable juvenile aquatic species. But when key species were removed from the salt marshes, the ecosystem was not able to function properly, thus limiting the performance of these services.
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