Crustose Coralline Algae

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Classification

Domain; Phylum; Class; Order; Family [Others may be used. Use NCBI link to find]

Organism

Crustose Coralline Algae

Kingdom: Eukaryota

Phylum: Rhodophyta

Class: Florideophyceae

Subclass: Corallinophycidae

Order: Corallinales

Family: Corallinaceae

NCBI: Taxonomy

Crustose Coralline Algae Click here to see a photo of crustose coralline algae

Description and Significance

Crustose coralline algae (CCA) are a variation of calcifying red autotrophic algae and comprise the third most diversified group of rhodophytes in marine environments today. They are found around the world in marine environments ranging from polar areas to the tropics, but they are more abundant in the warmer regions. They were some of the first to pioneer the growth of coral reefs beginning in the Paleozoic Era and are commonly found together today. They serve CCAs are a large contributor to the earth’s carbon cycle as well.

Defining characteristics of CCA include a densely packed filamentous body, calcite containing cell walls, and pit connections linking cells together. Of the CCA, two subgroups are categorized by their growth patterns. These include articulate and non-articulate (sometimes referred to as genicular or non-genicular.) Articulate CCA grow upright with branches. These branches are usually about 5-15 um wide and can be up to 0.5 mm tall. Non-articulate CCA are thinner and cover more surface area. They can sometimes have “knobs” that can be up to 2 cm high, but they do not branch like their counterparts. Click here to see the difference between genicular and non-genicular CCA

Genome

While the entire genome has not yet been sequenced, the mitochondrial genome of Corallina officinalis, a species of CCA has been sequenced. It consists of 26,504 bp and has a gene content consisting of 23 protein-coding genes, 26 transfer RNA genes, and two ribosomal RNA genes, with an overall GC content of 30.1%. Another group performed transcriptomics on four different species of CCA and found 978 orthologous protein groups uniquely shared amongst themselves.

Cell Structure, Metabolism and Life Cycle

CCA are one of the few species that calcify, along with other minerals such as aragonite. These calcifications are found both extracellularly and intracellularly as well as within the cell wall. These minerals typically contain magnesium and are deposited by an “organic matrix-mediated process.” This means that this process is considered to be somewhat regulated by the cell itself but is mostly a biologically induced process. Calcification is believed to stem from mineralizing seawater and organic compounds coming into contact with crystalline cellulose synthase complexes and build from these interactions. Click here to see a scanning electron microscope (SEM) photo of the calcified thallus of CCA

CCA are photosynthetic autotrophs that use solar energy to synthesize necessary sugars for their biological processes. A trait common only to red algae is the lack of amylose in their produced starches. Secondary metabolites of CCA are of interest. These algae synthesize anti-grazer compounds that are believed to reduce microbial pathogens because of their reduced palatability and digestibility or even potential nervous or cardiac effects.

CCA are asexual organisms that reproduce by sending spores into the open water. The spores develop into male and female gametophytes while bispores are produced from time to time as well. Fertilization occurs in carpogonium and produces diploid offspring that grow into asexual organisms. The cycle is repeated and has been for millions of years. This specific order of algae are known for being very slow-growing typically reaching at most 8 inches in height. Click here to see a diagram of the CCA life cycle

Ecology and Known Roles in Symbiosis

Some consider CCA the unsung architects of coral reefs. Dating back to the Paleozoic Era, they were some of the early pioneers of reefs and provided a structure that decreased overall erosion and allowed other marine cements and substrates to accumulate. This accumulation provided shelter for microbes and small organisms including corals. Corals were held in place by Because of their solitary position, they grew and colonized in the same areas where CCA were found. All of these factors introduced more diversity to the areas and thus coral reefs became hubs for organisms ranging from microbes to complex fish.

Like coral reefs, ocean acidification also greatly impacts CCA. Mineral levels of these organisms are directly related to thallus thickness and growth rate. As CaCO3 becomes a more expensive substrate to make, competition within algae-algae interactions and algae-grazer interactions become more influential. As the pH of the oceans becomes more acidic, crustose algae are some of the first to suffer as they are less fit to handle more acidic conditions. Corals and CCA will suffer if this acidification continues to increase, and because of their symbiosis, the damage will be two-fold.

Fun Facts

CCA have genicular joints that allow them to move congruently with different water currents more easily. Because of this, they are more rugged and capable to withstand higher physically stressful environments. These joints are segmented, increasing their flexibility and allowing their protrusions to move freely about the water. This trait evolved as CCA moved into areas closer to shorelines where they are commonly found today.

References

Aguirre, J (2010) “Integrating phylogeny, molecular clocks, and the fossil record in the evolution of corralling algae (Corallinales and Sporolithales, Rhodophyta)” Paleobiology

Belliveau, SA (2002) “Effects of Herbivory and Nutrients on the Early Colonization of Crustose Coralline and Fleshy Algae.” Marine Ecology Progress Series

Bilan, MI (2001) “Polysaccharides of calcareous algae and their effect on the calcification process.” Russian Journal of Bioorganic Chemistry

Bosence, DWJ (1983) “Coralline algal reef frameworks” The Geological Society

Johansen, HW (1981) Coralline Algae, A First Synthesis CRC Press

McCoy, SJ (2015) “Coralline Algae (Rhodophyta) in a Changing World: Integrating Ecological, Physiological, and Geochemical Responses to Global Change” Journal of Phycology

Nash, MC (2019) “Coralline algal calcification: A morphological and process-based understanding” PloS one

Ordoñez, A (2014) “Effects of Ocean Acidification on Population Dynamics and Community Structure of Crustose Coralline Algae” The Biological Bulletin

Page, TM (2019) “De novo transcriptome assembly for four species of crustose coralline algae and analysis of unique orthologous genes” Scientific Reports

Viola, R (2001) “The unique features of starch metabolism in red algae” Proc Biol Sci.

Williamson, C (2016) “Complete mitochondrial genome of the geniculate calcified red alga, Corallina officinalis (Corallinales, Rhodophyta) Mitochondrial DNA Part B

Author

This page was authored by Jaden S. Pounds as part of the 2020 UM Study USA led by Dr. Erik Hom at the University of Mississippi.