The mediterranean isn't known for its diversity of life... you won't find the vast array of colorful fish that inhabit the reefs of the Red Sea, nor will you see the complex habitats of the North Atlantic kelp forests. Much of the inshore western mediterranean is composed of vast lawns of sea grass interspersed with rocks and the occasional wreck, and supports a limited range of sea life. The med has undergone several cycles of drying out, and the sea life within it represent the descendents of a relatively recent recolonization over the last 5 million years.
One advantage of this reduced diversity is that when you are in the med, rather than being distracted by a variety of fish, you can pay more attention to what they are actually doing. One interesting behavior I noted was of clusters of seabream and wrasse feeding on the rocks... the smaller Rainbow Wrasse and Ornate Wrasse would hover around the larger seabream and Ocellated Wrasse, letting them do the heavy lifting of tearing chunks of algae and encrustations off the rocks, before diving at the debris cloud to grab any interesting food morsels that were shaken free.
You can see some of this behavior in the first half of the clip below, where off to the right several small wrasse are diving through one such cloud of debris, from where a seabream has pulled away some of the encrustations. Near the end of the clip is a different behavior - a watchful Painted Comber assessing my intentions before deciding that discretion is the better part of valour and fleeing into a nearby cranny.
For those interested in which fish is which, the two larger fish in the above photos are the White Seabream (oval with one tail spot) and Two-Banded Seabream (oval with two stripes), while the Ocellated Wrasse is the large wrasse with a small spot near the tail. There are two species of smaller wrasse in the photos and movies - the wrasse with a red stripe interrupted by a black bar is a male Mediterranean Rainbow Wrasse, while the female of the species has the dark upper body and light colored underside. The orange wrasse with the light bands and black spot near its back is an Ornate Wrasse.