What exactly does rainsfords or hectors gobies eat?

[Tripod1404]

I know they shift sand and graze on the live rock for copepods and algea. But when they shift sand, what do they filter out to eat? Unlike other sand shifting gobies that take a large deep bite out of sand and filter the worms and crustaceans inside , rainsfords or hectors gobies seem to only shift the top layer of the sand. What is exactly in that top layer that they shift?
I am curious because I have a rainsfords goby that is fat and growing but I actually never understood what it is eating. It rarely grazes on live rock but constantly shifts sand. I see some copepods and planaria worms on glass but I am not sure if the population is large enough to support the goby?

 

[Myles]

my rainford's seemed to have a liking for spaghetti worms.
Myles

 

[MondoBongo]

it has been my assumption that they're getting benthic life like copepods, etc... from the sand sifting, and also algae.

i've seen mine picking at different kinds of algae, even grape caulerpa and hair algae, from time to time.

so my guess is that they're getting a little bit of everything in that top layer of sand.