Marine biogenic calcification
The resulting structures, such as shells, skeletons, and coral reefs, function as protection, support, and shelter and create some of the most biodiverse habitats in the world.
Marine biogenic calcifiers also play a key role in the biological carbon pump and the biogeochemical cycling of nutrients, alkalinity, and organic matter.
A range of biochemical calcification (biocalcification) mechanisms exist, indicated by the fact that marine calcifiers use different forms of calcium carbonate minerals.
[11] This can make it difficult for marine organisms to precipitate and maintain their calcium carbonate structures, affecting growth, development, and overall health.
[15] Meanwhile, others state that from a physiological standpoint there are numerous marine organisms, and their calcification control is attributed more so to the concentrations of seawater bicarbonate (HCO3−) and protons (H+) rather than the Ω.
[16] Further research is essential to gain a comprehensive understanding of the intricate connections between Ω, ocean acidification, and their impacts on the calcification rates of marine biogenic calcifiers, elucidating the distinct roles played by each.
Coral reefs, physical structures formed from calcium carbonate, are important on biological and ecological scales to the regions they are endemic to.
Mollusks employ a strategic approach to protect their soft tissues and deter predation by developing an external calcified shell.
Adult sea urchins are a particularly popular species studied to better understand the molecular and cellular processes that the calcification and biomineralization of their skeletal structures requires.
[22] Unlike many other marine calcifiers, echinoderm tests are not formed purely from calcite; instead, their structures also heavily consist of organic matrices that increases the toughness and strength of their endoskeletons.
This links molting cycles to calcification processes, making access to a regular source of calcium and carbonate ions crucial for the growth and survival of crustaceans.
These large bloom formations are a driving force for the export of calcium carbonate from the surface to the deep ocean in what is sometimes called “Coccolith rain”.
[30] The magnesium-rich calcium carbonate of Corallinales cell wall provides shelter from predators and structural integrity in the intertidal zone.
[36] Heterococcoliths develop inside intracellular vesicles, with coccolith formation showing a unity ratio with photosynthetic carbon fixation under high calcification rates.
[39] The evolution of biogenic calcification and carbonate structures within the eukaryotic domain is complex, highlighted by the distribution of mineralized skeletons across major clades.
[40] Phylogenetic insights highlight repeated innovations in carbonate skeleton evolution, raising questions about homology in underlying molecular processes.
[40] Skeleton formation involves controlled mineral precipitation in specific biological environments, requiring directed calcium and carbonate transport, molecular templates, and growth inhibitors.
Biochemical similarities, including the synthesis of acidic proteins and glycoproteins guiding mineralization, suggest an ancient capacity for carbonate formation in eukaryotes.
[40] Skeletal organisms that precipitate massive skeletons under limited physiological control show stratigraphic patterns corresponding to shifts in seawater chemistry.
[49] Marine biogenic calcifiers, such as corals, are facing challenges due to increasing ocean temperatures, leading to prolonged warming events.
[51] When sea surface temperatures exceed the local summer maximum monthly mean, coral bleaching and mortality occur as a result of the breakdown in symbiosis with Symbiodiniaceae.
[15] Coral calcification is a biologically mediated process influenced by the regulation of internal calcifying fluid chemistry, including pH and dissolved inorganic carbon.
[15] Decoupling the effects of temperature and light on calcification processes is challenging due to their seasonal co-variation, highlighting the need for further research to address this gap and enhance our understanding of how marine biogenic calcifiers respond to future climate change.
Projections indicate that by the end of the century, mussel and oyster calcification could witness substantial reductions of 25% and 10%, respectively, as outlined in the IPCC IS92a scenario, which has an emissions trajectory that results in atmospheric CO2 reaching approximately 740 ppm in 2100.
The anticipated decline in calcification due to OA not only jeopardizes coastal biodiversity and ecosystem functioning but also carries the potential for considerable economic losses.
[58] Damaged shell surfaces, primarily resulting from reduced calcification rates, contribute to a significant decrease in sale prices, marking a critical economic concern.
[59] Furthermore, when accounting for assumed pH-driven changes occurring concurrently, quasi-profits diminish even more substantially, reaching levels of 49% to 84% across diverse OA scenarios.
[60] These findings emphasize the urgent need for proactive measures to mitigate OA's impact on bivalve farming and underscore the importance of comprehensive climate policies to address these multifaceted challenges.
As calcifiers play crucial roles in maintaining marine biodiversity, the repercussions of coral reef decline extend beyond economic considerations, emphasizing the urgency of comprehensive conservation efforts.
Extensive degradation is occurring in the Caribbean and Western Atlantic region's coral reefs, stemming from issues like disease, overfishing, and a range of human activities.
