Kelp Aquaculture in Frenchman Bay

Information compiled by Chris Petersen and Addie Huckins

Growing kelp or other algae species on line is less common than growing shellfish, but in Frenchman Bay, this is currently carried out by one commercial aquaculture operation, Springtide Seaweed.

Springtide Seaweed, founded by Sarah Redmond, grows multiple varieties of seaweed on lines.  On their website, they describe four types of seaweed that they currently cultivate: sugar kelp, skinny kelp, alaria, and dulse. They also have a seaweed nursery and processing facility in Gouldsboro. In addition to raising kelp, they’re also consultants for new aquaculture businesses and do aquaculture research. 

Kelp has a winter growing season, extending from fall to spring. A considerable amount of growth occurs in springtime with increasing temperatures and light levels. In Maine, the overall season runs from October to May. Lab culture occurs during early fall, from August to September, and seeded strings are outplanted sometime between September and November. Field culture occurs from November to mid-March. The kelp harvest season is in spring, between mid-March and May. 

Kelp cultivation

There are three primary components in kelp culture: inoculation, lab culture, and field culture. For inoculation, reproductive tissue from wild kelp must be collected and processed. Kelps have a multi-stage life cycle made up of a microscopic gametophyte (sexual phase in plants and algae) phase that grow from spores produced by the larger frond-like sporophyte (asexual & dominant phase in plants and algae) stage. Collection of sporophyte tissue happens manually by diving or accessing wild kelp at low tide and cutting blades containing healthy sorus tissue: the dark area at the center of the kelp blade containing the sporangia (spore-forming structures). Spore release from the sorus tissue is stimulated through a process of desiccation and rehydration. Culture strings can then be inoculated or “seeded” by encouraging wild collected spores to settle directly onto seed string. Strings can also be seeded by isolating individual gametophytes from lab cultures or wild stock, and producing young kelp blades through the fragmentation of gametophytes in the lab. The second method requires more advanced nursery lab space and more robust maintenance, but allows for more genetic control and ability to produce specific strains and can allow for year-round inoculation of seed spools. A sterile indoor nursery is required for inoculation and lab culture while field culture or grow-out occurs on longline systems in the ocean. Growing the microscopic phase of kelp requires cultivation in sterile natural seawater (inoculation & lab culture) as gametophyte development occurs through several stages influenced by environmental factors that can be manipulated in a lab setting. Once seed plants have settled, matured, and developed into juvenile sporophytes on a seed string, this string can be planted out on horizontal suspended long-lines where juvenile sporophytes can develop to the larger adult phase (field culture). Many kelp nurseries offer pre-seeded spools for purchase by growers. Kelp are subtidal species, meaning the seabed where they grow is below the lowest tide. Long lines must be submerged at a depth allowing for full coverage of the lines at low tide, but with enough sunlight penetration for photosynthesis.

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