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PHYCOLOGICAL SOCIETY OF AMERICA
Caloplaca coralloides
Ecology
Caloplaca coralloides is found at Hopkins Marine Station in Monterey living on exposed granitic rock surfaces in the lower supralittoral zone. Very few macroscopic organisms are living on these rocks. In this sense, C. coralloides is taking advantage of habitat that appears to be not easily livable. In fact, lichens are often the pioneers of inhospitable environments. There are lichens that can survive in some of the coldest and hottest places on earth. For example, some lichens can survive temperatures of 70 degrees C if they are in a dry state. Additionally, many lichens can fix nitrogen (those with cyanobacteria—C. coralloides does not) and break up rocks, processes that over long periods of time can make the local environment more hospitable to other organisms. The lichens on the rocks in the supralittoral zone at Hopkins Marine Station in Monterey, CA seem to be loosening bits of the surface of the rocks they are living on by growing their rhizines down into little fissures in the rocks.
The only other macroscopic photosynthetic organisms growing along with C. coralloides on the rocks directly above the intertidal zone at the Hopkins Marine Station are other lichens; one is a small orange lichen called Caloplaca luteominia var. luteominia. Only the bright orange apothecia of this lichen are visible because the thallus often grows entirely within the rock. The apothecia are mostly 0.6 to 1.2 mm in diameter.The other lichen is also crustose and growing its thallus down into the rock. It has a grey, white and black thallus. The apothecia have black hymenia surrounded by white. This black and white lichen was not successfully identified. Both Caloplaca luteominia var. luteominia and the black and white lichen grow right up next to C. coralloides and may be primarily responsible for loosening bits of the rock by growing their thalli down into the rock.
C. coralloides is considered a marine lichen if one uses the definitions of “marine” and “maritime” used by Sernander (1912, 1917) and Degelius (1939). “Species restricted to seashores, directly influenced by seawater, either by waves or spray, are marine. Species living above the marine zone, influenced by airborne salt, but not the saltwater itself, are maritime” (Arup, 1995b).
Living in a marine environment, C. coralloides is also often exposed to salt spray, high humidity and periods of foggy weather. Lichens can absorb moisture directly out of the air through their thallus. This also means that lichens are very affected by salt exposure from saltwater spray. In fact, the main factor that influences local distribution of maritime lichens is the amount of salt spray they are exposed to. Another important determining factor is the amount of light exposure.
The main cortical pigment in C. coralloides is parietin, an anthraquinone that functions as a sunscreen for the lichen. Studies have been done on Xanthoria parietina, another lichen that has parietin as a major cortical pigment, exploring the photoprotectant qualities of parietin for the lichen. Parietin absorbs light in the blue light and UV range (Gauslaa, 2003). It therefore makes sense that C. coralloides is an orange lichen. Those are the light waves that it is reflecting! Both blue light and UV light are high frequency waves and protection from them is important for lichens such as C. coralloides that live in very light exposed sites.
C. coralloides lives mainly in the lower part of the supralittoral zone on exposed rock surfaces, and is therefore sometimes exposed to intense levels of irradiation. C. coralloides grows mostly on vertical or somewhat vertical surfaces. It is possible that this preference helps lower the amount of photodamage sustained by the lichen. The C. coralloides in this picture is growing on a North West facing rockface at the Hopkings Marine Station in Monterey. There is conspicuously no C. coralloides growing on the opposing rockface, which, due to its more southerly orientation, gets more sun. The majority of the C. coralloides growing at Hopkins followed this trend. It is possible that this selection of North facing substrate is a technique for reducing photodamage along with the selection of more verticle surfaces.
C. coralloides is similar in many respects to another rock dwelling species of Caloplaca, Caloplaca brattie. However, unlike Caloplaca brattiae, C. coralloides avoids rocks covered in bird excrement.
At the Hopkins Marine Station in Monterey, C. coralloides lives on weathered granite, which is rich in silicates. Chemically different types of rock often have different lichen flora; however, lichens do not absorb nutrients or minerals from their substrate through their rhizoids. Perhaps a lichen prefers a particular substrate because it can absorb minerals from rainwater that runs over the substrate and part of the thallus. Or, perhaps the specific mineral content or the pH of a particular substrate is more conducive to the survival of a lichens photobiont in early stages of growth or helps with the germination of that lichen’s spores.
There are lichens distributed on all continents. However, C. coralloides is endemic to the west coast of N. America. 20 species of Caloplaca live on seashore rocks in continental N. America. C. coralloides ranges from Baja California Norte to Oregon. Just north of this northern limit there are not suitable rock substrates for C. coralloides to grow on. Because C. coralloides is rock-dwelling it is restricted to coastal regions with rocks, glacial boulders or pebbles. A possible reason why C. coralloides and other marine and maritime lichens do not grow on arctic shorelines is that there is too much ice scouring (Brodo).Photosynthesis in lichens proceeds best at 50-70% water saturation while respiration happens at highest rates when the lichen is completely or almost completely saturated with water. Therefore, dried out lichen do not photosynthesize or respire very much, and are somewhat dormant. This condition does not permanently damage most lichens. When returned to metabolically activating conditions, within a short time lichens can resume metabolizing.
The optimal levels of irradiation for photosynthesis differ depending on the photobiont. Green algal photobionts, such as that in C. coralloides, function better under higher levels of irradiance than do cyanobacteria.
Maximum rates of photosynthesis occur at moderate temperatures while maximal rates of respiration occur at higher temperatures.
Therefore, lichens tend to do best where it is moist and light with moderate temperatures.
© 2005 Megan Kelso