Blog

By: Angela De Palma-Dow

Crawling, creeping, and swimming under the surface in some Santa Monica Mountain creeks and streams lurks a red, crunchy and clawed troublemaker.  The red swamp crayfish (Procambarus clarkii) is an invasive species because it does not originate from California.  Like other invasive species, once crayfish became established here, they can cause damage to the environment, the economy, social or public health sectors.  The red swamp crayfish is native to areas of Louisiana, Texas, and Mexico, but have been observed in some Santa Monica Streams since the 1960s¹. Red swamp crayfish are particularly harmful to stream ecosystems in southern California because they have no native competitors or predators to keep their population levels in check. There are historically no native crayfish in southern California streams to compete with red swamps for food or living space.  Additionally, in most Santa Monica Mountain streams, there are no longer any large native game fish to prey on these invasive crustaceans.  Without active management and removal of the crayfish, they will continue to cause significant damage to the aquatic resources of Santa Monica Mountain regions. These crayfish negatively affect stream ecosystems by:

• Consuming both juvenile fish, amphibians and their eggs^1,2,3
• Reducing beneficial aquatic plants by eating them and digging them up²
• Reducing the density and variety of aquatic insects (which serve as food for fish) by directly consuming them and changing the stream bed habitat which serves as their home^2,3
• Negatively altering water quality when they dig and burrow into sediments and stream banks making the water turbid and less inhabitable by native species³

Since 2010, MRT based in Calabasas, with the help of regional volunteers, have been actively removing invasive crayfish in the Malibu Creek Watershed.   This is very important work not only because the Malibu Creek watershed drains into the Santa Monica Bay, but also because its tributaries are also home to many important native species.  Native fish such as the Arroyo Chub and the southern Steelhead Trout, as well as amphibian species such as Pacific tree frogs and the endangered California Newt have all shown a decline in numbers or have disappeared entirely in creeks where red swamp crayfish are present^1. Thanks to the ongoing efforts by MRT to remove crayfish, aquatic habitats have the chance to rebound and once again provide a natural home for our native species.

Want to get involved with MRT’s effort to remove crayfish from Malibu Creek Watershed?

Mountains Restoration Trust has several Crayfish Removal Open House events every month that you can participate alongside restoration professionals helping removing invasive crayfish from Malibu Creek Watershed streams. Check our calendar of events page <https://www.eventbrite.com/o/mountains-restoration-trust-3176893670 >to see what opportunities are coming up.  Do you belong to a group or organization that wants to support MRT and our invasive species removal efforts?  Contact our volunteer coordinator at volunteer@treepeoplelandtrust.org.

1. Red swamp crayfish can be identified by their typical red coloration and red dots on their claws and carapace (body).

2. While most are bright red, not all red swamp crayfish are red like their name indicates. Females or immature males can be brown or tan in color, but all red swamp crayfish will have raised dots along their claws and carapace (body).

Sources cited in this text:

1. Milligan, W.R., Jones, M.T., L.B. Katz, T.A. Lucas, and C.L. Davis. 2017. Predicting the effects of manual crayfish removal on California newt persistence in Santa Monica Mountain Streams. Ecological Modeling 352: 139-151.
2. Lodge, D. M., C. Taylor, D. Holdich, and J. Skurdal. 2000. Nonindigenous crayfishes threaten North American freshwater biodiversity: lessons from Europe. Fisheries 25(8):7–19.
3. Klose, K and S. D, Cooper. 2012. Contrasting effects of an invasive crayfish (Procambarus clarkii) on two temperate stream communities. Freshwater Biology 57:526-540.