Mudcracks are very common phenomena but in most cases barely worth photographing. Last december when I was in Gran Canaria I spotted larger area near the sea that was full of nicely formed mud polygons.
The formation of mudcracks probably needs no explanation. They are desiccation cracks which means that they form when wet fine-grained sediment loses its water content and contracts. Mudcracks are common in dry muddy areas which are subject to occasional flooding. In this particular case it was most likely seawater that inundated fine-grained sediments behind coastal pebble bar that now separates it from the ocean.