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  • Writer's pictureDaniel Yim

Emergent Mussels

Updated: Jul 13, 2020

Tradition in the Face of Climate Change

There was a saying in my old marching band. “Once is new, twice is coincidence, three times is tradition.” While it was meant to be a joke about how easily “traditions” or annual practices are established, the saying has haunted my thoughts lately because it weaves together both my thesis research and current events.

My research question asks, “how does an invasive species affect the abundance and number of species in a local environment?” It’s a question that has been asked a multitude of times, but not in the specific context I’m exploring. The invasive species I study is the ribbed mussel, Geukensia demissa. It hails from the United States Atlantic coast and was first spotted in South San Francisco Bay in 1894 (1, 2). Commonly found attached to the stems of Spartina cordgrass in salt marshes, the ribbed mussels grow in dense aggregations, half buried in the mud (3, 4). In their native habitat, the ribbed mussels form a mutually beneficial relationship with the local cordgrass where the mussel gets a solid surface to attach to and grow, and the cordgrass receives fertilizer from the mussel’s excretions, allowing it to grow much larger than cordgrass without mussels5.

These ribbed mussels, like the cordgrass they are attached to, are considered an ecosystem engineer, which is a species that creates, destroys, or modifies the habitat in some way (6). Generally, nonnative ecosystem engineers, in particular bivalves, can have pervasive and drastic effects on the local community such as increasing the density of invertebrates, which can have effects across the food web (7). However, scientists don’t know how the ribbed mussels affect the local invertebrate community in the San Francisco Bay.

To address this knowledge gap, I have collected ribbed mussels and created plots out in a Bay area salt marsh with three different density levels: one where the ribbed mussels are absent, one at the average ribbed mussel density for that salt marsh, and one at the highest density of ribbed mussels found on the U.S. Pacific coast (8). Sediment cores will be taken to sample the invertebrate community that has gathered over the months since these plots have been deployed. By comparing the abundance and species diversity of invertebrates at these different densities of ribbed mussels, it will lend me insight into what the community could be in the future if the ribbed mussels become more abundant.

This is pertinent information as there is reason to be concerned about the potential effects of the ribbed mussel. The ribbed mussel only reproduces during summer in its native range, but in Venezuela, where the ribbed mussel has invaded the warmer tropical waters, it can reproduce year round (9, 10). This research aligns with other findings that bivalves like the ribbed mussel show different reproduction in tropical systems primarily due to warmer waters (11). The ocean warming trend due to climate change, in combination with marine heat waves entering San Francisco Bay and coastal waters, presents a potential future where the ribbed mussels in our bay switch reproductive lifestyles and support much higher densities than currently seen (12, 13).

My research is still ongoing, and I am still working to get preliminary data. But as I ponder my research question and its relation to climate change, current events such as the recent climate strike and the IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate have called my attention to this emerging tradition of scientists demanding policy action on climate change from our policymakers led by youth and women of color.

The traditional wisdom of communicating science is to let the data and facts speak for themselves. Scientists regularly provide their data to inform policy decisions, but actively petitioning or advocating for policy change was frowned upon. Today, cultural circumstances and ideas on scientific communication have changed. It is practically impossible to be a graduate student without having to reckon with the question of how you plan to communicate your science, especially in the face of climate change.

And what is my answer? How will I communicate my research and knowledge to the world? I have taken part in a local climate strike, I have written letters to my representatives calling for climate policies, and I have spoken on the urgency of my research to the general public. I have made my tradition and I encourage my colleagues to do the same.


  1. Cohen, A. N. and Carlton, J. T. (1995). Non-indigenous Aquatic Species in a United States Estuary:  A case study of the biological invasions of the San Francisco Bay and Delta. US Department of Fish and Wildlife Service Report.

  2. Stearns, R. E. C. 1899. Modiola Plicatula Lamarck, In San Francisco Bay. Nautilus 13: 86

  3. Josselyn, M. (1983). The ecology of San Francisco Bay tidal marshes:  A community profile. U.S. Fish and Wildlife Services, Division of Biological Services, Washington D.C. FWS/OBS-83/23. 102pp.

  4. Bertness, M. D. and Grosholz, E. (1985). Population dynamics of the ribbed mussel, Geukensia demissa:  the costs and benefits of an aggregated distribution. Oecologia. 67:  192-204.

  5. Bertness, M.D. (1984). Ribbed Mussels and Spartina alterniflora Production in a New England Salt Marsh. Ecology. 65(6): 1794-1807.

  6. Crooks, J. A. (2002). Characterizing ecosystem-level consequences of biological invasions: the role of ecosystem engineers. OIKOS 97: 153-166.

  7. Sousa, R., Gutiérrez J. L., Aldridge D. C. (2009). Non-indigenous invasive bivalves as ecosystem engineers. Biological Invasions 11: 2367-2385.

  8. Torchin, M.E., Hechinger, R.F., Huspeni, T.C., Whitney, K.L., Lafferty, K.D. (2005). The introduced ribbed mussel (Geukensia demissa) in Estero de Punta Banda, Mexico: interactions with the native cordgrass, Spartina foliosa. Biological Invasions. 7: 607-614.

  9. Chesapeake Bay Program, (2004). "Bay Field Guide" (On-line). Atlantic Ribbed Mussel. Accessed May 20, 2019 at

  10. Severeyn, H. (2005). Reproductive cycle of Geukensia demissa (Bivalvia: Mytilidae) on a beach at Nazaret, El Moján, Zulia State, Venezuela. Ciencias Marinas. 31(1A): 111-118.

  11. Freites, L., Cordova, C., Arrieche, D., Montero, L., García, N., Himmelman, J.H.. (2010). Reproductive Cycle of the Penshell Atrina Seminuda (Mollusca: Bivalvia) in Northern Waters of Venezuela. Bulletin of Marine Science. 86. 785-801. 10.5343/bms.2009.1077.

  12. Levitus, S., Antonov, J., Boyer, T., Stephens, C. (2000). Warming of the World Ocean. Science. 287(5461): 2225-2229, DOI: 10.1126/science.287.5461.2225

  13. Chao, Y., Farrara, J., Bjorkstedt, E., Chai, F., Chavez, F., Rudnick, D., Enright, W., Fisher, J., Peterson, W., Welch, G., Davis, C., Dugdale, R., Wilkerson, F., Zhang, H., Zhang, Y., Ateljevich, E. (2017), The origins of the anomalous warming in the California coastal ocean and San Francisco Bay during 2014–2016, Journal of Geophysical Research: Oceans, 122, 7537– 7557, doi:10.1002/2017JC013120.

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