Nancy Foster Scholar Lindsay Marks Takes On Invasive Species

The kelp forests of Channel Islands National Marine Sanctuary provide shelter and food for hundreds of species of animals and plants, from abalone to sea lions. So how does an invasive seaweed impact this important ecosystem?

Nancy Foster Scholar Lindsay Marks is finding out. A doctoral student in Marine Ecology at the University of California, Santa Barbara, Marks is investigating Sargassum horneri, a non-native alga that was discovered in Channel Islands National Marine Sanctuary in fall 2009. S. horneri, a native of the waters near Korea, Japan and China, has the potential to outcompete native kelp and impact local ecosystems. This alga can drift long distances when detached from the sea floor, whether it's been pulled up by strong wave action or torn up by boat motors or anchors.

Lindsay Marks stands amoung the removed Sargassum horneri
Nancy Foster Scholar Lindsay Marks with removed Sargassum horneri. Photo: Sam Ginther

In S. horneri's annual life cycle, Marks explains, "dense carpets of small recruits appear in the summer and fall, limiting the availability of space on the reef for other benthic species" that would normally make up the kelp forest ecosystem. In the winter, a dense canopy forms, limiting the amount of light that can reach the reef below.

In recent years, southern California has seen anomalously warm water. While many local species of seaweed require cooler water, S. horneri has thrived in these new temperatures. As a result, Marks says, this invasive alga has become abundant where typically, giant kelp -- the foundation of southern California kelp forests -- would grow.

under water view of Sargassum horneri around Channel Islands National Marine Sanctuary
Sargassum horneri was discovered in and around Channel Islands National Marine Sanctuary in fall 2009. Photo: Tom Boyd,

It's a "dramatic shift," she says. "The magnitude of this invasion is unprecedented on southern California reefs" and resource managers and scientists alike are concerned about the ecological consequences.

diver removing Sargassum horneri
Marks removing S. horneri. Photo: Tom Boyd,

To find out just how this invasive species is impacting the sanctuary and surrounding waters, Marks has conducted dive surveys and experiments. To learn whether it's outcompeting giant kelp and other native species, she performs experiments in which she removes S. horneri and monitors the extent to which native species recover. She also clears areas of S. horneri to evaluate whether removal will help sanctuary managers control its spread. Finally, she explains, her surveys and experiments will help determine "whether robust kelp forest communities, such as those found in historic Marine Protected Areas, may resist invasion by S. horneri through increased competition by native algae."

area where sargassum has been removed
An area of removed S. horneri as part of Marks' research. Photo: Tom Boyd,

She's also helping spread the word: "despite its continuing spread and extreme abundance," she says, "awareness about the invasion is limited and monitoring its expansion is challenging." In partnership with the University of California Santa Cruz, she has created a website with with educational information and resources for identifying and reporting S. horneri.

landscape view of sargassum underwater
S. horneri near Channel Islands National Marine Sanctuary. Photo: Tom Boyd,

Marks developed this project when she applied for the Dr. Nancy Foster Scholarship, which provides support for independent graduate-level studies in ocean-related fields. She had been doing ecological research in kelp forests for six years at that point. When developing a research proposal for her application, she says, "I became so interested in the invasion that I began doing the work before I learned I won the award!" Her research plays a key role in understanding and fighting this invasion: understanding the ecology of S. horneri will enable resource managers to control its spread and impact on local kelp forest ecosystems.