Research Summary

Billions of Batillaria: A Battle between Snails Elucidates Details of Biological Invasions

In some places on the ESNERR - such as the panne on Hummingbird Island - small mud snails Batillaria attramentaria reach ridiculous densities. However, Batillaria is not native to the United States. This snail is native to Japan and probably arrived here accidentally in shipments of Asian oysters. It's been introduced to many estuaries along this coast where Asian oysters were brought in, but isn't found in those areas without a history of oyster-culturing, suggesting this was the primary means of introduction.

A very similar-looking species, Cerithidea californica or the Californian horn snail, is native to many West Coast estuaries, including Elkhorn Slough. In past decades, the native horn snail has gradually been disappearing from our estuaries, while the Japanese mud snail has been increasing. What is responsible for this pattern? Why is the invader doing better than the native?

Jeb Byers, our past Graduate Research Fellow, completed some superb research addressing these questions. He has already published half a dozen papers in prestigious journals detailing his findings. In a nutshell, he discovered that the invader has the competitive edge over the native for a number of reasons.

First of all, the invader only has one trematode worm parasite that infects it, while the native has 18 species that trouble it. Presumably that's an advantage of invading a new place - you leave some of your enemies behind.

Secondly, the invader invests less in shell strength than does the native. A thick shell may be a deterrent against predation, but snail predators have not yet been identified in the Slough. However, the cost of a thicker shell is slower growth. Jeb's experiments showed that the invader is more efficient than the native at converting food resources (benthic diatoms) into growth. And larger size means higher reproductive output.

Finally, Jeb found that the invader is more tolerant than the native of low oxygen conditions, which can give it an edge in human-influenced habitats that have low oxygen due to nutrient inputs and eutrophication.

Thanks to Jeb's experiments, we now understand the mechanisms by which the invasive mud snail is managing to displace the native horn snail. He has also developed and tested predictive models, that can be applied to other invasive species. We're proud that our Graduate Research Fellow has helped us to understand this ubiquitous snail of Elkhorn Slough, and has contributed to the scientific discipline of invasion biology.

Publications resulting from this research include:

Byers, J. E. 1999. The distribution of an introduced mollusc and its role in the long-term demise of a native confamilial species. Biological Invasions 1(4): 339-353.

Byers, J. E. 2000. Competition between two estuarine snails: implications for invasions of exotic species. Ecology 81(5): 1225-1239.

Byers, J. E. 2000. Differential susceptibility to hypoxia aids estuarine invasion. Mar. Ecol. Prog. Ser. 203: 123-132.

Byers, J. E. 2000. Effects of body size and resource availability on dispersal in a native and a non-native estuarine snail. Journal of Experimental Marine Biology and Ecology 248(2): 133-150.

Byers, J. E., and L. Goldwasser. in press. Exposing the mechanism and timing of impact of non-indigenous species on native species. Ecology.