How do crabs, shrimp, starfish, etc. play into # of fish?

[yourpalcm]

I have kept three freshwater tanks for a number of years. I'm finally going to take the plunge into Saltwater...
I'll be setting up a 75 gallon aquarium. I've seen all of the varying advice in stocking an aquarium. (1/2" per gallon, 1 fish per 10 gallons, etc.)
But what about crabs, shrimp, starfish, urchins, etc. How do they affect the stocking of your fish? If I've stocked the tank with what is the "appropriate" amount of fish, how does that then affect how I stock my tank with shrimp, starfish, urchins and/or crabs???

 

[ophiura]

Well, people have different opinions on this, but IMO they do eat, produce waste, and therefor contribute to the overall bioload of the system.
But it is hard to generalize, eg, X# of shrimp is equal to 1" of fish. So ultimately what it comes down to in the end is how your tank is running...what the parameters are like. What types of inverts you get (eg algae eaters like snails versus things you actively feed) also makes an impact. I think over time with the tank people find a balance that just works for them. You'll find a lot of questions about "how many snails for this size tank" etc and that is a good place to start.