South of Tampa Bay, in Florida, wedged between a quiet neighborhood and a mangrove forest, custom-designed aquariums are home to thousands of sea-urchin larvae that tumble and drift through the water.

Marine biologist Lauren Burk leaned down and squeezed out several ounces of a nutritious soup of amino acids, phytoplankton and brine shrimp from a pipette into a kiddie-pool size tub filled with two ...