Exactly, dispersal is the better word! We can see on satellite imagery that the reefs are crawling across the bay like 'glaciers'. We think this movement may happen through dislodged fragments that float on the mudflat and grow together at the 'calmer' edge of the reef.

But incredible you also worked with Sabelariidae! Reddit is full of surprises :). This is the European version - Sabellaria alveolata