Crustose

Crustose is a habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer.

[1] Some species of marine algae of the Rhodophyta, in particular members of the order Corallinales, family Corallinaceae, subfamily Melobesioideae with cell walls containing calcium carbonate grow to great depths in the intertidal zone, forming crusts on various substrates.

[2] The substrate can be rocks throughout the intertidal zone, or, as in the case of the Corallinales, reef-building corals, and other living organisms including plants, such as mangroves and animals such as shelled molluscs.

Crustose lichens have been found in deserts, ice free parts of Antarctica, and in the Alpine and Arctic regions.

CCA acts as the main food source for certain fish including parrotfish and Scarus trispinosus.