According to Official Guinness Records,
The largest human image of a seashell has 1,093 participants, and was achieved by The Beaches of Fort Myers & Sanibel (USA) as part of National Seashell Day at the Outrigger Beach Resort on Fort Myers Beach, Florida, USA, on 21 June 2018.The final seashell measured approximately 49.27 m (161 ft 8 in) long by 22.25 m (73 ft) wide. The gathering for National Seashell Day also functioned as a non-perishable food drive. The United Way of Lee, Hendry, Glades and Okeechobee Counties collected over 129.27 kg (285 lb) of food, which was donated to the InterFaith United Way House.
For a complete list of 2018 records, please visit 2018 Guinness Records in United States.