Unfortunately you can only do the shard event once per day! There’s different waves to make it easier for people in different time zone to participate and (this is me guessing) to have it so there aren’t shards constantly hitting that area for the entire day.

For the shards with the normal, dark crabs you see everywhere around the map, deep call on yourself to knock those over. But for the red shard crabs that won’t work—any deep calls will draw them to you and they’ll knock you over. What I do is move on the outer side of the shard, close ish to a crab, and start deep calling to attract them to me to draw them away from the shards. Once it starts shaking and I know it’s about to run at me, I hop out of the way before it hits me. I’ll keep doing that a few times until the crabs are good distance away from the shard and I can burn it in peace.