The Ten Thousand Islands form a 35-mile labyrinth of mangrove islets and oyster bars between Marco Island and Everglades National Park, a shallow-water archipelago where tidal currents deliver Gulf shells to barrier beaches twice daily. The islands are not numbered but named by fishermen and naturalists: Panther Key, Coon Key, Rabbit Key, each a crescent of white sand backed by red mangrove thickets that shelter wading birds and juvenile tarpon. The shelling grounds shift with every storm, and the best finds—junonia, lion's paw, lightning whelk—appear after a spring tide or a west wind overnight. Marco Island sightseeing and shelling tour operators launch from Goodland, Caxambas Pass, and Rose Marina, running flat-bottomed skiffs and pontoon boats shallow enough to reach the outer bars. The routes follow the intracoastal channels south toward Cape Romano, where the dome houses stand ruined in the surf, or north into the mangrove tunnels that open onto hidden lagoons. Bottlenose dolphins hunt mullet schools along the cuts, and manatees surface in the warm-water pockets near Rookery Bay. The islands themselves are uninhabited, part of the Ten Thousand Islands National Wildlife Refuge, and captains time arrivals to coincide with falling tides that expose the richest shell beds. Shelling is regulated: live mollusks must be returned, and sand dollars taken only if bleached. The best specimens lie at the tide line or half-buried in the shallows, identifiable by color and heft. Seasonal variation matters—winter northeasters churn the Gulf floor and push deep-water shells onto the beaches, while summer calms favor smaller varieties like coquinas and augers. Guides carry field keys and can distinguish a banded tulip from a true tulip by the aperture shape alone. The marco island sightseeing and shelling tour experience is tidal and weather-dependent, never the same route twice. Departures run year-round, though July and August bring afternoon thunderstorms that shorten the window. Morning trips offer cooler air and better light for dolphin sightings, while the Gulf remains glass-flat before the sea breeze builds. The return leg often includes a slow pass through the rookery islands, where roseate spoonbills and wood storks nest in the mangrove canopy, visible from April through September when the colonies are active.