Kelp is increasingly recognized as a valuable crop in marine aquaculture due to its rapid growth and minimal environmental inputs. Unlike terrestrial farming, kelp cultivation is a multi-step process that manipulates the alga’s natural life cycle in a controlled setting before transfer to the open ocean. Successful cultivation requires careful planning, starting with selecting an ideal marine environment. The entire cycle, from initial spore collection to final harvest, typically takes six to seven months.
Selecting the Cultivation Site
Selecting the cultivation site is crucial, as the location must meet the specific biological needs of the growing algae. Kelp species, such as sugar kelp (Saccharina latissima), are cold-water organisms that thrive best when water temperatures remain cool, ideally between 5 and 15 degrees Celsius. Temperatures exceeding 20 degrees Celsius can be lethal, necessitating sites with consistent cool water flow.
Water quality must be clean and unpolluted, with sufficient nutrient availability, particularly nitrate and phosphate, which kelp absorbs directly. Since kelp is a winter crop, it utilizes the high concentration of nitrogen that naturally peaks in coastal waters during colder months. A moderate current flow, often around 20 centimeters per second, is beneficial because it constantly replenishes nutrients and prevents waste accumulation.
Farm sites are typically located in shallow coastal waters, but must be deep enough to keep the kelp lines fully submerged during low tides. Avoiding areas near freshwater runoff is important, as optimal growth requires a salinity concentration of 33 to 35 parts per thousand. Preliminary research, including long-term monitoring of water parameters, is essential before deploying any infrastructure.
Preparing the Seeded Lines
The process of creating kelp seed begins by collecting fertile reproductive tissue, known as sorus, from healthy, wild parent plants. The sorus is identifiable as a dark section on the kelp blade. This tissue is cleaned, dried, and placed into chilled, sterile seawater, which stresses the tissue and triggers the release of millions of microscopic spores.
These spores are used to inoculate the cultivation substrate in a controlled hatchery environment. The substrate is thin nylon or cotton twine, called seed string, which is wrapped around PVC pipe sections to create “spools.” The spools are submerged in the spore solution in a dark environment for about 24 hours, allowing the spores to settle and attach firmly to the twine.
Once settled, the spores develop into microscopic male and female gametophytes. The spools are then transferred to nursery tanks where temperature, light, and nutrient levels are strictly controlled for four to eight weeks. Maintaining the water temperature at 10 to 12 degrees Celsius and providing nutrient-enriched media supports growth. After fertilization, the gametophytes develop into tiny juvenile sporophytes, which are visible as a fine, brown fuzz on the seed string.
Establishing the Farm Infrastructure
When juvenile sporophytes on the seed string reach 1 to 5 millimeters, typically by late fall or early winter, they are ready to be outplanted to the open-water farm site. The farm infrastructure is a longline system designed to suspend the kelp at an optimal depth. The system is anchored at both ends by heavy mooring blocks, such as 2,000-pound concrete blocks, connected via chain and mooring lines.
These moorings secure the main horizontal grow lines, or longlines, which are thick, durable synthetic ropes often extending 400 to 1,000 feet. The longlines are deployed parallel, typically spaced 10 to 15 feet apart to prevent tangling and ensure adequate water flow and nutrient delivery. Subsurface buoys and weights, called droppers, are incorporated along the longlines to maintain the ideal growing depth of 6 to 8 feet below the surface.
Outplanting involves transferring the seeded twine from the hatchery spools onto the thicker longlines using a small boat. One end of the seeded twine is secured to the longline, which is then threaded through the spool. As the boat moves, the spool unwinds, wrapping the seed string tightly around the main grow line in a continuous spiral. This technique ensures a high density of juvenile kelp is evenly distributed.
Monitoring Growth and Harvesting
After outplanting, the kelp farm requires continuous monitoring throughout the winter and early spring grow-out phase. Farm managers routinely check water quality parameters and assess growth rate by measuring the biomass of plants in a designated section of the grow line. Visual inspections are also regularly performed to check for signs of biological stress or the onset of biofouling.
Biofouling is the growth of competing organisms, such as bryozoans, crustaceans, and other algae, on the kelp blades, and it is a primary factor in determining harvest timing. As water temperatures begin to warm in the spring, typically approaching 10 degrees Celsius, the rate of biofouling increases rapidly, which can quickly degrade the crop quality. Maturity is assessed by the thickness and dry weight of the blades, which represent the net biomass, rather than simply measuring length.
Harvesting usually occurs in late spring or early summer, before the warm water severely impacts the crop. The process is labor-intensive, requiring a boat or harvest barge to haul the heavily laden longlines out of the water. The line is slowly lifted to a height that allows workers to efficiently cut the mature kelp blades near the stipe, sometimes leaving the holdfast and meristem intact. The harvested kelp biomass must be handled immediately, often by chilling or freezing, to maintain its quality before it is transported for processing.