The Sargassum

The white and red coast guard boat left Portland and made Metinic Island in an hour. As the boat pulled up, just off the main dock, Captain Gabriela "Gaby" Salinas pulled out her binoculars. Her bottom lip began to quiver as she strained to make out something on the island.
-Something or someone is moving out there, she said, Tommy, go out to the bow and light up the shoreline with the torch.
Lt. Tom Riegler went out on deck and flipped on the piercing search light. 15,000 lumens lit up the dark shoreline. What they saw made the hair stand up on their forearms and on the backs of their necks.
-Jesussss, Captain Salinas breathed out...what in the hell...