* Founders include MySQL creator, others from MySQL

HELSINKI, March 6 (Reuters) - The Finnish founders of open-source database MySQL saim to invest in more European software firms through their Open Ocean Capital fund, which they see growing to 60 million euros by May, up a third from a year earlier.

On Tuesday, Open Ocean said it, along with French venture firms Alven Capital and ISAI, would invest $5 million in French start-up Commmerce Guys, which makes open-source software for online stores.

More investments in software firms are in the pipeline, it said.

"Assuming stock markets and exit markets will recover at some point, this is a good time to start," said Open Ocean partner Tom Henriksson, former chief of Nokia's mobile marketing business.

Open Ocean was founded in 2009 by MySQL leaders, including the database's creator Michael "Monty" Widenius, who sold MySQL for $1 billion to Sun Microsystems in 2008. MySQL is the most popular open-source database and was a key factor in Oracle's subsequent $7 billion acquisition of Sun.

Open Ocean invested in early-stage start-ups such as Web Of Trust, MoSync and SkySQL in its first 6 million euro ($8 million) funding round. In May 2011 it announced a further round of 40 million euros, which it seeks to grow to 60 million by May this year.

Henriksson said the fund was particularly interested in investing in companies that have strong developer and user communities, similar to MySQL, as start-ups can't afford to hire many developers.

• A Permanent Economic Emergency