Sana Javeri Kadri leaned heavily on Instagram for marketing when she started her spice company, Diaspora Company, in 2017. “I completely credit them for our growth — and then the algorithm changed and our sales dropped horrifyingly,” she said. “There was a point where I was having dreams that Instagram could go back to the way things were, and my nightmares were about all the reasons why that was impossible.”

Since joining Instagram, Diaspora’s following grew to more than 100,000. “Up until three months ago, we never paid for ads on Instagram,” Ms. Javeri Kadri said, though the company has used public relations agencies. “These aren’t hard numbers, but we used to see 2,000 to 3,000 likes on most posts for our 100,000-person audience,” she added. “Now it’s like 200 to 300.”

Since Instagram arrived in 2010, sharing food photos, writing a thoughtful caption and adding relevant hashtags have been the foundation of many small food businesses’ social media strategy, and a low-cost form of advertising. Then, at the end of 2021, Instagram’s parent company, Meta, changed the platform’s algorithm to prioritize videos, called Reels. Accounts that don’t regularly post the short-form videos appear below those that have embraced the format in users’ Instagram feeds, resulting in a notable drop in engagement on posts — and, in turn, sales — for many small businesses.

“With the way Instagram has shifted everything to video, it has really decreased the amount of traffic we get to our Instagram account, and that means to our website,” said Skyler Mapes, a founder of Exau Olive Oil. “You have to fight harder than ever to get out there and get seen.”

Adam Mosseri, the head of Instagram, announced the change in a video posted to his Twitter account in the final days of 2021. “We’re going to double down on our focus on video,” Mr. Mosseri said. “We’re no longer just a photo-sharing app.”

He added that the company is focused on growing Reels, which was introduced in August 2020 as an obvious reaction to TikTok’s success. Reels appear on an Instagram user’s feed and the Explore content discovery page; the videos can be only one minute long and can be filmed and edited within the app.

The change has left small food companies and their social media managers flailing. Instagram feed captions have functioned as a direct line to consumers and a way to humanize brand accounts.

“It’s been terrifying because I was really good at taking beautiful photos and writing long emotional captions,” Ms. Javeri Kadri said, “and suddenly, for the past six months I’ve been mourning the loss of value of that skill.”

While the pivot to Reels doesn’t involve much writing, it does require video production experience. Instagram tells its users that successful Reels are high-quality; use text, filters and camera effects; are set to music and trending sounds; and are “entertaining and fun,” featuring content that “delights people, grabs their attention, makes them laugh or has a fun surprise or twist.”

This is no small feat for business owners and social editors who lack video-editing skills. Abigail Knoff, the marketing director at the mushroom company Smallhold, notes that it’s a much bigger lift for her team.

“The planning, editing and voice-over and music skills for more produced video content are very different from still iPhone photography,” she said.

Ms. Knoff is left with two options: “We can occasionally work with freelancers who are, rightfully so, higher cost, or be patient as we learn these new skills on the job.”

Some Instagram managers who have these skills still need to pay for outside help. Danita Evangeline White, who runs social media for Trade Street Jam Company, has noticed a 38 percent drop in reach, or the number of users who see the company’s content, over the past 90 days. Traffic to the company’s website is also down by one-third since the end of 2021. Ms. White has since incorporated more video on the company’s account, which has about 25,500 followers, but she believes that its content still isn’t being prioritized by the algorithm.

After considering its options, Trade Street Jam hired a social media consultant to do an Instagram audit. “Our founder is the only full-time employee; we don’t have much budget for outside marketing or consultancy,” Ms. White said, but “we thought the investment would be worth it.”

One newly favored way for a company to end reliance on Instagram’s algorithm: Move to another platform.

PJ Monte, the founder of Monte’s Fine Foods, turned his attention away from Instagram and toward TikTok. “With basically no followers on TikTok, I’ve had two videos gain a few million views,” Mr. Monte said.

Ms. Javeri Kadri also shifted her focus to TikTok, and, after six months, Diaspora had its own viral video. It grew the company’s following on the platform, she said, “but it’s not like TikTok is suddenly bringing in the bucks,” as the app doesn’t have integrated shopping features or links, as Instagram does. (The company declined to provide sales figures.)

Brands whose bottom lines remain unaffected are the ones that foresaw the inevitable algorithm change. Denetrias Charlemagne, a founder of Avec Drinks, avoided heavily investing in social media from the start, relying instead on press relations and word-of-mouth marketing.

“Our strategy was never to build on Instagram,” said Ms. Charlemagne, who has experience working in media. She pointed to Facebook’s decision to change its algorithm in 2018, which deprioritized brand accounts and reduced media companies’ traffic.

Ultimately, the success of small businesses on social media is in the hands of a few corporations.

“These platforms don’t belong to us, they belong to tech companies,” said Ms. Mapes of Exau. Now, as she has to “fight harder than ever to get out there and get seen,” she said, “I’m over it.”