The response of the polyps, however, is similar in that layers of compact, fine crystalline repair carbonate are deposited at points of attempted endolith penetration.
The nature of the defense response exhibited by corals in response to chronic interactions with endolithic fungi, and perhaps to less frequent interactions with endolithic algae, suggests a dependence on their ability to rapidly deposit [CaCO.sub.3] at sites of attempted endolith penetration.
Although reports of fungal and algal-like endoliths in corals date back almost 150 years (1) and evidence of a fossil history extends as far back as the Upper Devonian ([sim]370 ma) (2), most attention has been paid to the structure (3), function (4, 5), and diversity (6) of the coral-zooxanthellae interactions, ignoring the endolithic members of the consortium.
Dense populations of algal and fungal endoliths have been associated with black-stained bands in specimens of P.
Although skeletons of dead corals are bored by a variety of endolithic microorganisms, there has been no evidence that endoliths can penetrate the layer of tissue that covers living coral surfaces, leading to the conclusion that infestation by a limited number of specialized endoliths occurs early in the life of a coral, and that endolithic algae and fungi continue to grow in parallel with the accretion of the corallum (8).
Metabolism, although an essential component in defining complexity of animate matter, can remain dormant for extended intervals as in the slow metabolism of endoliths (93), life transitioning through a non-metabolizing seed or spore stage, extracellular viruses, and tardigrades.
For example, one component of complexification, maintaining a complex system, (as with endoliths), may be prioritized over other descriptors, such as advancing the degree and variety of complexity or advancing the net volume of complex matter, which may have lower priority.