Marine Conservation Ecology Lab

Department of Biology

San Diego State University

• Asian mussel abundance and distribution in Mission Bay
• Asian mussel interactions with native organisms

Asian mussel abundance and distribution in Mission Bay

Personnel: Cheng, Brian (MS student in Hovel lab)

Summary: For his master's thesis, Brian is investigating the processes that cause patterns of Asian mussel (Musculista senhousia) abundance in Mission Bay, San Diego. There are very large differences in mussel abundance among sections of Mission Bay, with mussel density > 10,000 per m2 in some areas, and near zero in other areas. This large variability in mussel density may be due to pre-settlement processes (larval settlement), or to post-settlement processes (predation on mussels, competition with other species, food limitation, physiological stress, etc.). Brian is conducting surveys and manipulative experiments throughout Mission Bay to determine what combination of these processes is most likely responsible for variability in mussel density. (Read more about Brian's project by clicking here).

Funding for this project is being provided by: the Edna Bailey Sussman Foundation, and the California Shore and Beach Preservation Association.

Presentations:

Cheng, B.S. and K.A. Hovel. 2007. Relative influence of predation and recruitment on the invasive Asian mussel. Southern California Unified Malacologists 11th annual meeting, San Diego, CA.

Asian mussel interactions with native organisms

Personnel:Kushner, Rachel (former undergraduate honors thesis student and MS student in Hovel lab; graduated with her MS in 2005).

Summary: Rachel conducted two studies on Asian mussels during her time at SDSU. First, for her undergraduate honors thesis, she studied how native predators respond to Asian mussel density. Asian mussels have thin shells, and are consumed by a variety of predators in Mission Bay and San Diego Bay. A snail called the festive murex, Pteropurpura festiva, is able to consume large quantities of mussels in certain areas of Mission Bay and San Diego Bay. Rachel exposed mussels to predators to determine if mussel mortality is density-dependent, and to determine the functional response of the festive murex to Asian mussel density. The answers to these questions are important because they indicate whether native predators are able to exert local control over mussel densities. She found that Asian mussel mortality was inversely density-dependent, and that the festive murex exhibited a type II functional response to mussel density, both of which indicate that native predators are unable to control Asian mussel densities. However, native predators were able to completely consume small patches of Asian mussels over periods of days to weeks, suggesting that invasion resistance to mussels may depend heavily on the size of mussel patches. Finally, in this project, Rachel found that eelgrass habitat structure did not alter patterns of Asian mussel mortality, though eelgrass habitat structure did influence the functional response of predators to mussels.

For her master's thesis, Rachel determined whether Asian mussels outcompete native bivalves in soft sediments of San Diego Bay, and whether native bivalves may be protected from predators by virtue of the fact that Asian mussels are palatable and abundant in Mission Bay and San Diego Bay. She held Asian mussels in caged plots with native bivalves to examine competition, and exposed mixed plots of native bivalves and Asian mussels to predators. She found that native bivalve mortality increased with Asian mussel density due to competition (likely the smothering of native bivalves by Asian mussel byssal mats), and that the likelihood of native bivalve mortality increased, rather than decreased when native bivalves were exposed to predators with Asian mussels.

Publications:

Kushner, R.B. and K.A. Hovel. 2006. Effects of native predators and eelgrass habitat structure on the introduced Asian mussel Musculista senhousia in Southern California. Journal of Experimental Marine Biology and Ecology 332: 166-177.

KAH January 4, 2007

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