This behavior was observed in June 2010, on the reef crest, just before the sunshine, end of low tide ...
Philibert Bidgrain
Réunion, l'Hermitage lagoon, less 1 m, 23 June 2010, size : 10-15 mm
Several specimens per m3, on the reef crest, end of low tide, just before the sunshine, 23 June
Only 10 specimens observed on 24 June...
And nothing on 25 June...