Lisa Matsumoto has expanded a children's book into a fully staged, two-act musical, but unfortunately, there's just not enough of "The Adventures of Gary & Harry — A Tale of Two Turtles" to fill it out.

After establishing herself as a playwright, actress and director with a series of fractured fairy tales done in pidgin, Matsumoto has turned to environmental concerns with a string of children's plays that focus on the need to preserve our fragile and special ecosystem.

In this one, the title characters protect a coral reef from pollution and over development. Both the show's concept and plot exist in that single line.

So the production now at the Hawai'i Theatre — written and directed by Matsumoto with music, lyrics and musical direction by Roslyn Catracchia — becomes an exercise in pumping up a small idea into a two-hour show.

The exercise leaves us exhausted.

First there is the breakneck speed. Lines fly by at such a rapid clip that at least a couple of major supporting characters fail to be understood for the entire evening. Acting becomes a contest of who can shout loudest and wave their arms hardest. And when they're not sounding like they came from elsewhere, the songs all tend to sound the same.

The production best succeeds visually. Daniel Gelbmann's set and Stephen Clear's lighting successfully suggest an undersea cove with colorful coral, dangling seaweed, and shafts of sunlight rippling in the underwater currents.

Hugh Hanson's costumes create animal characters from street wear outlines filled in with vivid colors, patterns and shapes. The jellyfish ballet sequence, choreographed by Hymie Huckso and Mara Bacon, stands out, with filmy streamers on the dancers and Michael Furuya's umbrella-shaped puppets to suggest those elusive creatures.

There are also some noble acting efforts.

Daryl Bonilla and Dwayne Fujitani stand out in small but memorable scenes as a couple of sharks, perhaps because they're the only characters to speak pidgin and because of Bonilla's laugh-line reference to his TV bank commercials.

Stephanie Sanchez is a slimy eel of a real estate sales agent and Sam Pablo and Kala'i Stern are the nice-guy title turtles, with Stern also pitching in on the musical direction. But there simply isn't enough show to go around as the heroes work to raise environmental consciousness. Too many TV references and too many undersea divas become annoying.

"The Adventures of Gary & Harry — A Tale of Two Turtles" is a little book that would best have remained so.