Possible Clues:

• Sealab inhabitant
• Undersea explorer
• One living under the sea for a period in order to observe and explore
• Sub tenant?
• Cousteau, for instance
• Cousteau, perhaps, has an alternative for us
• SEALAB inhabitant
• Sealab dweller
• Skilled underwater worker or scientist — an ace out (anag)
• Underwater explorer