By next summer, Maine Coast Sea Vegetables plans to move from Franklin to Ellsworth, into twice the space with better access to transportation.

Its products are sold under the brands Kelp Krunch, Sea Seasonings, Dulse and others. Its sheets of nori are used as wraps for sushi and California rolls.

With its products in Whole Foods, small chains and independent health food stores, Amazon and its own site (seaveg.com), the company’s sales are booming — and it has outgrown its existing patchwork production plant, which General Manager Seraphina Erhart calls “a rabbit warren.”

“We’re bursting at the seams,” Erhart said during a recent tour of the facility.

Erhart is the daughter of Shep and Linnette Erhart, who launched the business out of their home in 1971 to process edible seaweed. They processed 200 pounds of edible sea vegetables the first year. Maine Coast Sea Vegetables moved into its current building, a former production facility for a salmon farm, in 1993.

Over the years, the company added onto the building numerous times to accommodate processing, product development, storage and shipping. Today, it’s easy to get lost among ramps and stairs leading to multiple levels, out-of-the-way warehouses and backyard trailers.

That will change next summer, when the company moves within Hancock County to its new facility in Ellsworth, 12 miles from the current site. Construction is underway, and move-in will take place after the plant is equipped and certified organic.

It is expected everyone on the staff of 19 will stay on. The new space will accommodate up to 25 workers.

Shep Erhart credits Seraphina Erhart, who was hired four years ago, with bringing new energy to help fulfill his dream of having a custom-built facility that will include a research and development kitchen to allow cooks to test recipes and give public demonstrations.

The lobby will be devoted to public outreach. The owners hope to educate students and the general public about sea vegetables, including nutritional information and recipes. A sliding wall between the kitchen and a conference room will allow the space to become a classroom.

At 17,600 square feet, nearly twice the size of the current plant, the $1.5 million facility will have a better layout for storing raw ingredients, processing, packaging and shipping. The company got bank and Small Business Administration loans to finance the project.

“We built it for 10 years out, so yes, we will grow,” said Shep Erhart. “We’re not saying exactly how fast or what’s next, but we’re saying we need more space and we’d like to put new product on line.”

The company contracts with more than 50 harvesters. About 100,000 pounds are harvested along the coast from Bar Harbor to Eastport, but also from the waters around Grand Manan Island in New Brunswick. The harvest stretches from early April to late October.

About 60 percent of the harvest is dulse, which has a rich red color and is soft and chewy. It’s often used in soups and is primarily found around Grand Manan.

Other sea edibles include alaria, which favors turbulent areas and can be hard to reach, sugar kelp, laver, sea lettuce, bladderwrack, rockweed and Irish moss. All of those products are native to Maine.

Maine Coast Sea also buys 100,000 pounds of sea vegetables each year from other North Atlantic wholesalers, mainly in Iceland.

Like land vegetables, some seaweeds taste better raw, others cooked. Some are ground as condiments or for use as nutritional supplements in capsule form. Seraphina Erhart said the food is becoming more popular.

“Everyone knows what a sushi roll is now,” Erhart said. “That was not the case 20 years ago.”

Most of the world’s seaweed harvest is used for fertilizer, animal feed and extracts such as carageenan, a thickener.

According to Maine Sea Grant at the University of Maine, one of 33 NOAA Sea Grant programs, there are more than 250 species of sea vegetables in the Gulf of Maine. Most are edible, although not necessarily tasty. Fewer than a dozen are commercially harvested.

Rockweed has comprised over 95 percent of Maine’s seaweed landings by weight over the past five years. An estimated 16.7 million pounds of rockweed was harvested in 2013, compared with 468,900 pounds of other seaweeds.

Most of it is processed into two general product categories, nutritional supplements for animals and people, and concentrated fertilizers. With a total estimated value of $20 million per year, rockweed is one of Maine’s most valuable marine resources. It also is an essential component of Maine’s intertidal zone, providing food, shelter and spawning habitat for a variety of small marine organisms.

For all seaweeds, the Department of Marine Resources issues about 100 harvester licenses annually. It remains a small industry, employing a total of 115 workers on the waterfront and in plants. The Department of Marine Resources and industry are working on a management plan to assure rockweed is harvested sustainably into the future.

Regulations regarding sustainability are relatively minimal, especially compared to fisheries. But Shep Erhart said he requires his independent contractors to limit their harvest to 30 percent to 50 percent of a bed, depending on the species, a percentage he’s observed as sustainable over his 43 years in the industry.

While the industry remains small, Maine Coast Sea Vegetables is seeing increased demand. Originally, the products appealed to natural foods enthusiasts and consumers on macrobiotic diets. Today, the vegetables are touted for their nutritional value, including vitamins, calcium, and iron.

There are efforts to increase the amount of farmed, cultivated seaweed, prompted in part by two 2011 disasters.

Japan’s March 2011 Fukushima nuclear accident stirred fears of radioactive seafood products on the Pacific coast and created demand for Atlantic seaweed and seafood.

“Everyone was scared, so they were looking for seaweed they felt they could trust out of the Atlantic,” said Seraphina Erhart. “There was also a group of people who wanted to buy up as much as they could that had been harvested before Fukushima. So we did three months of sales in six weeks.”

Then, in August 2011, Hurricane Irene washed seaweed out to sea, reducing the year’s harvest.

“So we felt an increased demand on our supply and had less supply than ever,” Seraphina Erhart said. “That was around the time Shep started saying we needed to come up with new products and have more secondary products. We looked around and said, ‘Where and how are we going to accomplish that in this facility?’ The combination of all that happening, within a year, was a huge push for both the new facility and for farming. And it seemed we couldn’t do one without the other.”

The Erharts concluded they needed greater capacity to process farmed seaweed.

“The wild stuff trickles in over the course of a season, but a farm is more likely to produce a huge amount in a short period of time,” Erhart said.

In 2013, with a $19,842 grant from the Maine Technology Institute, Shep Erhart began working with the University of Maine’s Center for Cooperative Aquaculture Research in Franklin and the Sea Grant Cooperative Extension to develop seeded nets and ropes for aquaculture production.

Elsewhere, research and practice are coming together. Sea Grant’s research is advancing seaweed farming by building on research conducted by University of Maine professor Susan Brawley.

From Portland, Ocean Approved LLC, founded by Tollef Olson in 2006, is farming open-ocean sugar kelp. At a 35-acre site off Sorrento, in Frenchman’s Bay, Sea Grant marine extension agent Sarah Redmond is leading a collaboration that includes Shep Erhart and lobster fisherman James West. Redmond has been working with Brawley in the lab and setting up trials with shellfish farmers interested in seeding seaweed around existing harvest sites as a supplemental crop.

“There’s a lot of momentum, as a new industry,” Redmond said. “Ocean Approved is at the commercial scale and produce their own seed. Others are figuring out how to culture it. Every site is different and every situation is different, and none of that infrastructure has been established.”

Erhart said it will be five years before he gets a commercially viable crop.

“The good news is, it’s happening successfully elsewhere in the North Atlantic. We just have to figure out this particular bay and our particular parameters,” he added.

It could be that climate change, ocean acidification and invasive species will make farming an increasingly important part of the industry, he said.

“Climate change is happening in the seaweed kingdom as well as everywhere else on the planet,” Erhart said. “This year, we got enough wild-harvested seaweed, not as much as we did last year — and not more. So we may be at the threshold of sustainable harvest of the wild crop. It makes sense — if we’re going to meet increasing demand — that we cultivate it.”

At the same time, seaweeds are adapters.

“They’ve been through a bunch of ice ages,” he said. “They’re millions of years old. They’ve survived a lot of changes. And so will we.”