CAPE ROMAIN - Marsh Island and the White Banks are mist-like specks of land in the far waters of the national wildlife refuge here. All told, they are no bigger than the sliver of Crab Bank in Charleston Harbor.

They are too small, too far out and too hard to land on for a lot of boaters. So why bother to put them off limits? Brown pelicans, royal terns, tri-colored herons, snowy egrets - the species list just goes on and the number of nests are astounding.

Despite the islands' tiny size, and partly because they are so remote, they are among the most productive shorebird and wading birds rookeries in the state - in 2013, about 3,000 nests were laid. The islands are the key northern link in a chain of protected rookeries that includes Crab Bank, Skimmer Flats and Deveaux Bank near Charleston and Tomkins Island in the Savannah River delta.

"They're remote. They're hard to access with the tides. Marsh is mostly marsh and the banks are mostly shell shoals," said Sarah Dawsey, Cape Romain National Wildlife Refuge manager.

But they do get disturbed by anglers, shrimpers and recreational boaters, simply because they are the only ground out there for a ways. That's why starting last Saturday, landing on the islands will not be allowed again until fall, even on the low tide exposed beach.

The islands are the first of the seasonal closures for rookery islands.

Just how important islands like these are was brought out by a radio-tag study on oyster catchers a few years back, said Nathan Dias, of the Cape Romain bird Observatory.

Oyster catchers are thought to roost along the shore beaches they forage. The tagged birds gathered to roost on the shore in the evening, then flew to Marsh Island after dark.

"There aren't many places left where shorebirds and wading birds can roost without human disturbance," Dias said. "(Marsh and White Banks) are nesting islands, very valuable high tide and night roosts. The birds are very easily disturbed. People should keep their distance."

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