OLD TAMPA BAY — Sheila Scolaro took a long, deep breath. The salty air whistled first into her snorkel, and then her lungs, before she leaned forward and plunged into the murky depths of Tampa Bay. Cloudy green water hid the seafloor below. Looking through a diving mask, she could see a foot, maybe two, in front of her. Scolaro, a seagrass scientist, dove down with a question: How much .