Increasing interest in the production of low-carbon biofuels has turned attention to kelp as a green fuel feedstock. Unlike corn and other fuel crops, the brown seaweed does not require freshwater, fertilizer or land resources for cultivation. To exploit this bioresource, researchers demonstrated a new aquaculture technique on the California coast that significantly increases kelp growth, yielding four times more biomass than natural processes.

The method is based on a depth-cycling approach that physically moves the macroalgae between deep nutrient-rich water at night and shallow depths within the photic zone during the day to optimize growth. (A) The Buoy-Elevator experimental platform depth-cycled kelp between 9 m during the day and 80 m at night. (B) Parsons Landing was the site of collection for kelp used in the trial and also used as a reference for growth of kelp in its natural setting. (C) Kelp were outplanted along a polypropylene rope suspended at 9 m in the water column at Big Fisherman’s Cove, mimicking established near-shore farming practices. Source: Ignacio A. Navarrete et al.A kelp elevator consisting of fiberglass tubes and stainless-steel cables that support the kelp in the open ocean was engineered for this purpose. Juvenile kelp is affixed to a horizontal beam and the entire structure is raised and lowered in the water column using an automated winch.

The system was tested with giant kelp, Macrocystis pyrifera, off of Catalina Island. Over the course of 100 days, the kelp was raised to the sunny surface during the daytime and lowered to depths of around 260 ft at night so the plants could obtain the vital nutrients available in deeper waters.

Study results published in Renewable and Sustainable Energy Reviews by researchers from University of Southern California, Marine BioEnergy Inc (California) and University of California at Santa Barbara document faster growth for kelp assisted by the elevator mechanism relative to a control group. The depth-cycling system increased growth rate by 5% per day and increased biomass production fourfold.