Question

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Answer 1

Umm air, water pressure, I'm giving ideas, that is confusing.  They come out in high tide.

Answer 2

The observation states a number of things. First, These crabs are territorial to the burrow they live in. This means that they each stick to their own and will defend theirs if necessary. During high tide they are underwater and during low tide they can be exposed. Now the limiting factors are things that could limit these creatures.

So some limiting factors that I can see based off this information is during low tide they are exposed to predators and are more likely to be harmed during that time than during high tide. 

Another limiting factor is they are territorial which means they stay in the same area. This might not be dangerous predator wise but when they are located near each other food may be harder to get. 

Finally also pertaining food, the tides could effect when they get food, it may be harder for them to get food during high tide then it is during low tide. 

Hope this helps. Feel free to ask me any more questions! Thanks.