Photoautotrophic Euendoliths and Their Complex Ecological Effects in Marine Bioengineered Ecosystems

Abstract

Photoautotrophic euendolithic microorganisms are ubiquitous where there are calcium carbonate substrates to bore into and sufficient light to sustain photosynthesis. The most diverse and abundant modern euendolithic communities can be found in the marine environment. Euendoliths, as microorganisms infesting inanimate substrates, were first thought to be ecologically irrelevant. Over the past three decades, numerous studies have subsequently shown that euendoliths can colonize living marine calcifying organisms, such as coral skeletons and bivalve shells, causing both sub-lethal and lethal damage. Moreover, under suitable environmental conditions, their presence can have surprising benefits for the host. Thus, infestation by photoautotrophic euendoliths has significant consequences for calcifying organisms that are of particular importance in the case of ecosystems underpinned by calcifying ecosystem engineers. In this review, we address the nature and diversity of marine euendoliths, as revealed recently through genetic techniques, their bioerosive mechanisms, how environmental conditions influence their incidence in marine ecosystems and their potential as bioindicators, how they affect live calcifiers, and the potential future of euendolithic infestation in the context of global climate change and ocean acidification.

Epibiont of venus clam (Gafrarium tumidum) shells: a study on Pari Island, Seribu Islands

“…Euendoliths are a diverse group of microorganisms that inhabit various substrates such as rocks, coral skeletons, and mollusk shells [39][40][41]. They actively bore into soluble substrates like phosphate and carbonate, and examples of these organisms include cyanobacteria, red microalgae, and green microalgae [41]. We suspect that the biofilm on the shells of G.tumidum is composed of cyanobacteria.…”

“…The green biofilm that adheres to the clam shells is likely composed of photoautotrophic euendolithic microorganisms. Euendoliths are a diverse group of microorganisms that inhabit various substrates such as rocks, coral skeletons, and mollusk shells [39][40][41]. They actively bore into soluble substrates like phosphate and carbonate, and examples of these organisms include cyanobacteria, red microalgae, and green microalgae [41].…”

Euendolithic Infestation of Mussel Shells Indirectly Improves the Thermal Buffering Offered by Mussel Beds to Associated Molluscs, but One Size Does Not Fit All

“…Photoautotrophic euendoliths refer to a heterogeneous group of microorganisms (i.e., cyanobacteria, chlorophytes, and rhodophytes) that live and actively bore into relatively soluble substrates, such as phosphate and carbonate substrates (e.g., coral skeletons, bivalve shells) [35][36][37]. Present essentially anywhere there is sufficient light for photosynthesis and a suitable substratum to bore into, photoautotrophic euendoliths readily infest marine calcifiers (i.e., corals, bivalves, crustose coralline algae), with both negative and positive effects [38]. In addition to its negative sub-lethal and lethal effects on mussels [38][39][40], euendolithic infestation causes a distinctive discolouration of the mussel shell as a by-product of its corrosive activity, thereby increasing its albedo [33,34].…”

“…Present essentially anywhere there is sufficient light for photosynthesis and a suitable substratum to bore into, photoautotrophic euendoliths readily infest marine calcifiers (i.e., corals, bivalves, crustose coralline algae), with both negative and positive effects [38]. In addition to its negative sub-lethal and lethal effects on mussels [38][39][40], euendolithic infestation causes a distinctive discolouration of the mussel shell as a by-product of its corrosive activity, thereby increasing its albedo [33,34]. Since they reflect more light, infested mussels display lower body temperature and greater survival rates than non-infested mussels during heatwaves [34,41].…”

“…This beneficial effect of euendolithic infestation extends to both infested and non-infested neighbouring mussels but is restricted to periods of intense heat and desiccation stress [31,41,42]. It is anticipated that GCC and ocean acidification will coincide with increased rates, prevalence, and severity of euendolithic infestation of mussels [38]. Investigating the potential impacts of euendolithic infestation of mussel beds on the thermal buffering they provide to associated species is critical to predicting how intertidal ecosystems will react to GCC in the future.…”