Patch reefs are located behind the reef flat or barrier reef and are typically located in shallow waters of 10-20 feet in depth. They're small and isolated coral skeleton islands that form a circular or oval shape. The outer edge of each patch reef is completely surrounded by sand that extends to meet deeper sea grass meadows. This sandy area is formed by the distance that herbivorous fish feel is within safe foraging range from the patch reef. Patch reefs are highly variable in both size and development and contain species that are adapted to living on the open reef but are much more protected. Species found in this habitat include hard coral, soft coral, gorgonians, sponges, sporadic colonies of macro algae as well as adjacent sea grass beds. Because of the lack of nutrients in this particular habitat, macro algae are much more limited in diversity here. Depending on the location of the reef, many open water macro algae thrive in this environment, including calcerous algae such as Halimeda, Gracilaria, Halymenia, Haliptilon, Liagora and other calcified encrusting red algae. Dictoya is also a dominant algae species on the reef, but its growth is smaller and more compact due to the strong current and lack of available nutrients. 

Patch reefs would certainly fall into the category of most mixed reef aquariums today. They're typically formed by stacking live rock high in the tank to create a wall on the back or the center of the aquarium. The rockwork is then filled with a combination of photosynthetic organisms including hard and soft corals, single specimens of macro algae and other invertebrates to form a miniature reef biotope. While this can be done attractively, a true patch reef would have a single collection of rocks arranged to appear as one structure located in the center of the aquarium. This type of aqua-scape is more suited to wide, shallow tanks so that a substantial area of sand can be arranged around the reef. 

The unique aqua-scape (pictured) of aquarist Jaide Swarthout mimics a miniature patch reef surrounded by sand and a surrounding sea grass bed. Notice the use of driftwood, which is normally seen in freshwater planted aquariums. This minimalist approach is very appealing and allows for easier maintenance