Connecting the South Bay Marsh by Howard Shellhammer
- For the sake of the salt marsh harvest mouse and all the other inhabitants of saltwater wetlands, marshes need to be reconnected. It is also important to recreate much deeper high marsh zones, and that might happen if many levees are rebuilt with gradually sloped bayward sides. As sea levels rise, such a configuration may be required to protect the mouse from extinction.
- The salt marsh harvest mouse, which weighs about as much as a 25-cent piece, lives in the upper half of the middle, or pickleweed, zone as well as in the high marsh, or peripheral halophyte, zone made up of salt-tolerant species that are infrequently inundated by the tides. In the past, this high marsh zone was a transition between the marsh and surrounding grasslands. Today there are virtually no grasslands. Mice that live near the upper edge of the marsh escape the highest tides by moving into the high marsh zone—if it is present and if there are appropriate tall plant species to provide the mice adequate cover. If not, the mice are easy prey for predatory birds when high tides force them up on top of the marsh vegetation.
- Today's marshes contain small populations of the mice, and small populations tend to have less genetic variability than larger ones. What was once essentially two populations of the mouse, one on each side of the South Bay, are now a few large and many small populations evolving separately.
- Historically, mice were not found among bulrush marshes, such as those that greatly expanded in the southern end of the South Bay in response to changing water conditions. About ten years ago, among mature bulrushes with five or six feet of thick thatch in them, more thatch than living stems, I found sizable populations of salt marsh harvest mice. What does that mean? I believe it means that alkali bulrush marshes can act as corridors between salt marshes; that they can act as reservoirs for the mice during hard times in the salt marshes.
- So what needs to be done? Connect the salt marshes of the South Bay. Give them deep upper edges, with gradual slopes toward the water. The pickleweed plains need to be deeper, with more complex vegetation, allowing mice and small birds to find cover during high tides. The value of mature alkali bulrush marshes needs more study.
- Finally it seems to me important not to build housing or industrial parks immediately adjacent to the marshes. We need room for marshes to grow as time passes and sea levels rise. We need those marshes, not only for the mouse but as nurseries for fish, nesting and feeding grounds for ducks and natural water cleansing areas. We also need them for something difficult to put a price tag on— their subtle and hopefully enduring beauty.
Mice Among the Bulrushes
Next Steps