[Off topic] Hawaii ocean bottom biology

This January I took my family to Big Island of Hawaii.  Got some tips from friends here; thanks a lot.  I only now have a chance to go back and process the tons of video/audio/pictures that were taken.  I am reminded of the scenary that puzzled me.

I only dove at 3 spots in Hawaii, all on west side of Bid Island, but all 3 have same phenamenon -- there is no vegetation on ocean floor.  There are lots and lots of fish, but no vegetation that I could see.  Does anyone know if this is typical of Hawaii oceans?  And if so, how does an ecosystem without vegetation work??  I thought food chain starts with some sort of vegetation...

I'm no expert, but that has been my experience as well.  Maybe it all starts with the corals.

I think there's small vegetation grows on the rocks in the picture.

My thoughts:
Haven't really looked in to it, but it's all mostly based off coral reefs. There is some algae that is growing on the substrate but not a ton. There is a lot of plankton though, including phyto which form the basis of the food chain. The reefs and various rocky areas form the substrate/structure to harbor fish which is mostly what the kelp and (non coral) reefs in ca do.

I'll type more when I get to my computer and not my phone