By: Lauren Smith

I am thrilled to be back at Wrigley this summer! I completed my last Catalina field season as a Wrigley Fellow on March 11th, 2020. Luckily, I finished collecting everything JUST under the wire before USC and my university (UCLA) closed for the pandemic.

My previous experiment was comparing how beach wrack of invasive Sargassum horneri compared as a resource subsidy with native kelp (Macrocystis pyrifera). When algae become dislodged, it washes ashore as beach wrack, which provides habitat to flies, amphipods, and other invertebrates. Those bugs provide trophic support for birds, which eat them and then deposit their guano in terrestrial communities. This marine resource provides nutrients in terrestrial communities.

I am interested in determining differences between an invasive species that has formed dense monocultures around Catalina Island and a native species that is foundational in our coastal kelp forests. I expected to find that Macrocystis would support more invertebrates and a larger diversity of invertebrates.

Emily Ryznar and I collecting algae to create beach wrack

To test my theory, I collected large bags of Sargassum and Macrocystis. With the help of my lab mates, I weighed them out into individual wrack piles wrapped in netting (40 total! 20 of each species). Weighing them was a little tricky, we normally use a low velocity centrifuge (salad spinner) to spin off excess water, however I don’t think they make a salad spinner big enough for this experiment. Instead, we spun the algae in mesh bags around our heads for one minute, which looked very silly.

Me spinning algae

Sargassum horneri wrack bundles ready to be deployed

Once the wracks were created and ready to be deployed, we anchored them along the beach below the Two Harbors Campground. To ensure they didn’t float away, we dug holes about 2ft deep, buried sand anchors and affixed the wracks to them.

Algae bundles along the wrack line

Once the experiment was in place, I collected 5 wracks of each algal species after 1 day, 3 days, 9 days, and 21 days. Although I am not quite done processing the data, I can tell you one thing:  Macrocystis pyrifera did not have more invertebrates than Sargassum horneri, quite the opposite!

Although, I was expecting to see Macrocystis have more bug activity, Sargassum wracks had a lot more bugs. It took at least twice as long to process a Sargassum wrack because there were so many bugs. I believe this is likely due to Sargassum being more tightly wound, it likely stays wetter longer which creates a more suitable habitat. This suggests that invasive Sargassum horneri would be able to maintain some ecosystem functions if kelp is lost, albeit these functions are not the same.

As I am wrapping up my beach wrack analysis, I have started thinking a lot about the work I’m planning for this summer. When I started graduate school, I thought that all of my work would be on Sargassum horneri, but sometimes a global pandemic forces you to make some changes. Since I haven’t been able to be in the field, some of my lab mates and I have started to think about algal traits (weight, height, thickness, toughness etc.) and what factors influence them. The more I read, the more interested I became, and this summer I’m excited to test out some theories from the terrestrial plant world in a marine setting and share what I find.

 Lauren Smith is a Summer Wrigley Institute Fellow, and a graduate student at UCLA.