Over the past decade, the Rocky Intertidal Zone at Cabrillo National Monument has been overrun by an invasive brown seaweed known as Sargassum muticum. This marine plant, native to Japan, is believed to have made it’s way to San Diego over 30 years ago through the ballast waters of ships. Invasive species, such as Sargassum, are hypothesized to lower the biodiversity of an area by outcompeting the native biota and overtaking all other available space. Therefore, Cabrillo Biologist and our lovely volunteers have been working on slowly removing this species from certain plots to better answer our question about the effects of invasive species on biodiversity. Our hope is that in the next 5 years we can revisit these sites to see if the brown wire weed does or does not influence biodiversity.

The invader: Sargassum muticum

During the summer in San Diego, the tides shift and it is difficult to experience a low tide during appropriate work hours. Cabrillo Biologists and I went out on the morning of July 12, 2017 at 6am to begin another phase of Sargassum removal. The process of removal is tedious and difficult to witness change overtime with the continuous growth of this perennial brown alga.

However, the benefit to this process is by far the creatures you inevitably get to see when you look a little closer into the intertidal zone. A fan favorite this week was this vibrant nudibranch (sea slug), Chromodoris macfarlandi. Remember to always keep exploring, even when working!

Nudibranch (sea slug), Chromodoris macfarlandi

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