Seizing the Moment with the SuperSucker
Authored by Ian Jacobson, LAW’s Dive Program Manager
Winter diving can be tough—and this year was no exception, with all of the storms that drenched LA. Luckily, they brought much-needed rain, but along with that, high winds and large surf! While we were waiting for the break in the weather, our patience paid off. Forecasts gave us a glimmer of hope to sneak out onto the water and begin what we have been planning since last year: putting the SuperSucker into action!
With a call out to our hardened volunteer divers, we filled the boat with our trusted team. We set out to remove that pesky invasive algae, Sargassum horneri, from our sites in Palos Verdes. Throughout the fall and winter, we have been monitoring the algae and tracking its growth. We’ve witnessed its transformation from a small recruit no larger than 5cm, to a mature adult plant over 100cm tall! The underwater landscape was vastly different than what we had seen before, where once we had to keep a keen eye out for small individuals. Now, the “horizon” was nothing but sporadic tall bushes that covered the reef in all directions.
We had one major goal, and timing was everything. We were setting out to remove S. horneri before it became fertile, which seems to be driven by the seasonal drop in water temperature in the winter months. By removing the algae before it has the chance to reproduce, we can effectively eliminate the opportunity for the standing population to contribute to the next generation, which we believe will increase the chances of success in curbing its establishment in the following months and into next year. When we arrived to our site, our initial descent into the depths confirmed that we were just in time. Surveys showed that the adult plants were in fact mature, but not yet showing any signs of fertility. The time we had been preparing for had come.
Fashioned with rubber mats, zip ties, and bungee cords, the SuperSucker securely sat on the back deck ready for action. Built in 2012, the SuperSucker is a small Subaru engine that functions as a suction pump, taking water and algae in through a hose, passing through a diaphragm, and pushing out onto a sorting tray where we separate out any bycatch that we return safely back into the water. The trick is “priming the pump” and as we attached all of the hoses to our device, we made sure to fill the system with plenty of water to maximize the suction we can generate on the bottom. With a pull of a cord, she fired up with ease and we geared ourselves up with our transect tapes and mesh bags for collection.
Underwater, we confined ourselves to the plots we had set up and monitored, making perpendicular lanes from a baseline transect that marked our boundaries. Swimming up and down, we plucked all plants we came across by a short, swift tug at the base of their holdfast, which is their disc-like structure that secures them to the seafloor. One by one we removed the sargassum until it was time to transport it to the surface. With filled bags, we located the hose from the SuperSucker and began feeding the algae into the intake hose. At first, one person held the hose steady, while the others fed the algae in, but the quick thinking of experienced divers led to a much more efficient strategy of propping it in between two boulders that secured the hose in place. From there on out, the process was streamlined with divers simultaneously removing and transporting sargassum from the reef to the surface. Two back to back days of this resulted in us clearing an area of over 300 square meters of reef with over 100lbs of algae removed!
Taking a look at the landscape post-removal was an interesting sight to see. Swaths of native algae, predominately the chain bladder kelp Stephanocystis osmundacea, were uncovered and showing their mature appendages free from the previously crowded space caused by S. horneri. The understory algae that was previously shaded by the canopy of S. horneri was now liberated and fully exposed to the sunlight that penetrated the surface of the water. In the months to come, we will be checking back to see the progress of our work and monitoring our plots throughout the year. Additionally, we will be monitoring adjacent plots that served as the controls to our experiment. We did not perform any removal of S. horneri in these areas and will be comparing these areas to our removal plots to determine if our efforts had any significant affects.
All in all, our operations were a smashing success! Now, it’s a waiting game to see what kind of impacts these efforts have on the reef. Since this species follows an annual life-cycle, we won’t be able to begin seeing the results until later this summer. In the meantime, we will focus our efforts on bigger plans to address invasive species as a form of Biological Pollution, and continue looking at the current state of sargassum to inform future actions. So far, we have put together the beginnings of a working group that is composed of researchers currently studying S. horneri. Stay tuned for more blog posts, in which our coalition will give sneak peaks into their work to shed light on the state of the sargassum invasion!