Shells are the only thing that the ocean brings to the shore from the millions of life form is sustains. Shells are calcium which has a significant thermal relationship with heat. Limestones come from this.
If Shells do not show up on the shores, it is the sign of global warming,
The warming of the ocean in particular.
Hence Shell or Sanghu or Conch has a special place in the tradition of this land. Every auspicious and beginning, from temple to temple war field or journey of the soul is announced with its sound which is the primary sound of creation.
Hence shown as an ornament in the hands of Vishnu the sustainer of life in the trinities.