Prawns as Snail Shell Inhabitants

Prawns or shrimps are Crustaceans, belonging to the Decapoda. Dendrobranchiata is the superordinate taxon representing prawns/ shrimps.
Shrimps mate between 3 hours and 4-5 seconds, depending on the taxon, to which they belong, and eggs usually are mostly shed directly into the surrounding water without brood caring.
On the Croatian Island Zlarin, I observed shrimps in a saltwater-pond, directly connected with the Sea, while they were in order to secure snail shells. This behavior was obviously due to have a safe refuge, which protects against predators. I don't know, whether these shrimps additionally also use to mate in front of these shells or whether they even deposit their eggs inside.
They were very active during the day and reacted quite "aggressive" also against my fingers, when I carefully put them inside the water. Usually, there seemed to be a competition for those houses on an intra-species level. This behavior is documented in this short film.