Marsh near Toms Point with spartina

Since 2001, Audubon Canyon Ranch has collaborated with the Invasive Spartina Project to monitor and remove the non-native, invasive cordgrass, Spartina densiflora, from Tomales Bay.

A lesser-known invasive Spartina that impacts San Francisco Bay and the nearby coast, S. densiflora, grows in expanding clumps that threaten wetlands by eliminating open areas used for foraging, particularly by birds. These dense clusters of cordgrass can alter marsh elevation, especially along the edges of channels and sloughs, by slowing water flow and trapping sediments.

Toms Point, an early Spartina hotspot

ACR’s Toms Point preserve, at the north end of Tomales Bay, was one of the first Spartina hotspots identified along the outer coast. Tomales Bay is an important wintering location for shorebirds, supporting roughly 20,000 in the early winter months. Toms Point is just north of one of the most significant winter foraging areas on the bay. The other—the recently restored Giacomini Wetlands—is only 12.5 km to the south.

What could have been a disastrous Spartina densiflora invasion on Tomales Bay, instead became an example of the value of early and concerted action. Working together, Invasive Spartina Project (ISP) and Audubon Canyon Ranch (ACR) stopped the cordgrass’s spread at Toms Point, its historic outbreak site, through annual monitoring and removal.

Anticipating a win

This June, amid the dreary COVID-19 atmosphere, we were encouraged that no S. densiflora plants were detected on the marsh. While exciting for invasive plant managers, the news was doubly heartening because it followed a consistent pattern of declining numbers at this site. The survey marked the third in a row where five or fewer small plants were detected and removed.

As there are no nearby sources of S. densifora to bring new seed into the bay, it’s likely that the seedbank at Toms Point is being steadily exhausted. We’re optimistic about the eventual eradication of this invader.

  • Aerial map showing Point Reyes Peninsula, Tomales Bay, Toms Point, and Cypress Grove Research Center
  •  S. densiflora, grows in expanding clumps

Staying the course

Tripp McCandlish, ISP’s Field Operations Manager, reports that ISP will continue to plan for “bi-annual surveys for densiflora at the historical infestations until we achieve five straight years of zero detections.” After the celebration, ISP will transfer the job of monitoring to ACR’s staff and volunteers.

It may be difficult, however, to keep the ISP crew away. Their field biologists consider a visit to Tomales Bay and Toms Point a treat. According to Tripp, even after several years of zero detections, “we plan to do a complete survey of Tomales Bay for hybrid Spartina and densiflora at least once every three to four years—as a reward to our staff and also as a preventative survey.”

ACR is grateful for the decades-long partnership with the Invasive Spartina Project to protect not only our sanctuaries, but also the whole of Tomales Bay. ISP’s open, collaborative approach greatly simplifies the difficulties of managing a species that ignores property boundaries and can be widely dispersed.

Learn more about the work of the Invasive Spartina Project here. This article originally appeared in Conservation in Action, Spring 2022, ACR's newsletter to our community. Read this article and more in the full edition of Conservation in Action, or share this article with a friend!