From past personal experience as an LAE at the operating airline; the Twin Otter has completely standard gear/tyres for its scheduled tide-dependant service to Barra; a TC holder's high-flotation option is available for the Twotter but not needed. Of course, Twin Otter stuff does not directly read across to other GA, and the company aircraft operating there have appropriate corrosion-control measures in the maintenance programme
Although Barra Airport is a beach, you don't just land on any convenient strip; its surveyed and marked. Its the mother of all beaches.
Other beaches, of course, can be sons of beaches.