Crustose is a habit of some types of

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. ''Crustose'' adheres very closely to the substrates at all points. ''Crustose'' is found on

rocks In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's ...

and

tree bark Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consist ...

. Some species of marine

of the

Rhodophyta Red algae, or Rhodophyta (, ; ), are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority ...

, in particular members of the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Corallinales Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of re ...

, family Corallinaceae, subfamily

Melobesioideae The Melobesioideae are a subfamily of Corallinacean Coralline algae with multiporate conceptacle Conceptacles are specialized cavities of marine and freshwater algae that contain the reproductive organs. They are situated in the receptacle and ...

with cell walls containing calcium carbonate grow to great depths in the intertidal zone, forming crusts on various substrates. 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

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

s. The coralline red algae are major members of coral reef communities, cementing the corals together with their crusts. Among the brown algae, the order Ralfsiales comprises two families of crustose algae.

Growth and habitat

Many

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.drought resistant climates. Crustose lichens have been found in deserts, ice free parts of Antarctica, and in the Alpine and Arctic regions.

Characteristics

Crustose can come in a variety of colors such as yellow, orange, red, gray and green. These colors tend to be bright and vibrant. Crustose is similar to other lichens because they share a similar internal morphology. The lichen's body is formed from filaments of the fungal partner. The density of these filaments determines the layers within the lichen.

Productivity

There are many variations of crustose, including Crustose Coralline Algae (CCA), found in three different habitats; flat, crest and slope reef. CCA are highly dependent on sunlight to grow in abundance, and their growth increases productivity. CCA acts as the main food source for certain fish including parrotfish and Scarus trispinosus.

References

Red algae {{Biology-stub