Investigating the invasive algae, Sargassum horneri, in Southern California
By Sadie Small and Genoa Sullaway
Picture a healthy garden. You may think of carefully tended flowers and a variety of plants that produce delicious vegetables. A gardener puts a lot of effort into this healthy garden to keep out certain weeds. These weeds can harm the other plants by sucking up water and nutrients, or by taking up space so that other plants don't have room to grow.
Weeds also exist in the sea. A species of recent concern is an invasive seaweed called Sargassum horneri
) that has arrived in Southern California.
A field of adult S. horneri
at Catalina Island, Channel Islands (Source: G. Sullaway).
This alga likely traveled from its native habitat in Japan to the U.S. West Coast via cargo ship ballast waters. Interestingly, the alga was first found on a dock in the international shipping port of Long Beach Harbor in 2003. Since then it quickly spread to the CA Channel Islands and to Baja, Mexico!
As indicated by the orange markers in the above map, S. horneri
has been documented in Southern California and Baja, Mexico. (Source: S. Small)
Why has it spread so quickly?
As humans travel around the world, they spread invasive species to new habitats. However, only some of these species end up persisting in the new habitat and threatening native communities.
Like invaders in a garden, S. horneri
has many “weedy” characteristics that help it colonize and dominate new habitats. For example, it grows more quickly than native algae species; in just one year, this annual species
can grow from being microscopic in size to 10 feet tall. To top it off, S. horneri
may be able to self-fertilize, so a single rogue alga can start a whole population! These traits have contributed to the rapid invasion of S. horneri.
Current Invasive Species Research at the SDSU CMIL
a Master's student in the Edwards Lab and the CMIL student manager, studies the invasibility of S. horneri by examining its responses to different environmental conditions.
Specifically, she looks at how different temperatures, salinities, nutrient concentrations, and light levels affect growth and photosynthesis of S. horneri.
Sadie conducts laboratory experiments to see if these responses differ among algae from different locations, or during different parts of their life cycle.
This environmental tolerance information can be used by management agencies to understand and predict the spread of this species.
, a Master's student in the Edwards Lab, studies how S. horneri affects native algae species. These native algae species are important because they provide habitat for many invertebrate and fish species and contribute to coastal primary production.
She examines how this invasion, and the related change in native algae, may alter the amount of photosynthesis, or primary production that occurs in these near shore algae-dominated habitats.
Researchers at CMIL and other institutions are discovering that when S. horneri
invades a new ecosystem, it takes advantage of open space on the seafloor and starts growing quickly. This disturbs the natural relationships between native algae, fish, and invertebrates. Over the course of an invasion, it appears that native algae species die off and the environment becomes dominated by S. horneri
Research by CMIL students will help us understand the important factors that influence species invasions in near shore habitats, as well as the magnitude of their effects on ecosystem services.
Author: Sadie Small and Genoa Sullaway. Contact Sadie and Genoa at email@example.com or find them on Twitter: @subtidalsadie and @genoasully.