That's one great looking mantis you have.
Wolf Park? Do you mean Seawolf Park in Galveston over the causeway?
I catch my crabs on the Dike. (wait that doesn't sound good.

)
When you exit Texas City off the freeway, just follow the highway into town, then continue all the way to the end. This will take you through the City. When you get to the small wall at the end you will see the Dike road to the right. Go down the Dike road over the levee and you will see all the granite rocks lined up on the right. They go the length of the Dike.
I walk on them until I find some flat ones that I can lay on and reach into the water fairly easily. I then reach down and feel around until I find some rocks to pick up. Usually no bigger than a football. Have a bucket of water ready about half full. When you bring the rock out of the water and turn it over, you will see all kinds of rock crabs and porcelain crabs. You need to know the difference if you want to add some procelain crabs to you reef. You cannot get them confused or you will end up with rock crabs in your reef. (bad, very bad)
To catch the shrimp, just use a large dip net from Academy. You also need a battery operated airpump for bubbles to keep anything you catch alive. Academy has some cheap d-cell ones that work great.
Actually if you want to call me at 409-945-2380 and come down to go with us to catch some stuff sometime, feel free. My wife, 5 year old and I go on weekends sometimes.
Mark