Color Our Reef ALive

Corals are most elegant bio-geochemical engineers, building their colorful homes out of sunlight and air. But why do they bleach when stressed and how can we help them relax?

Modern, shallow (sub) tropical reefs are made by hermatypic stony ‘scleractinian’ corals. They are colonies of polyps with stingy tentacles, like the related sea anemone, secreting calcium carbonate cups; the corallite, an exoskeleton in which they can retract.

Hermatypic corals are colored by pigmented unicellular algae that they host in their tissue at concentrations of several million per square centimeter. These algae are dinoflagellates known as zooxanthellae which photosynthesize, using sunlight and carbon dioxide to produce oxygen and organic compounds, which they share with corals in exchange for nutrients and protection.

When corals are stressed, for example by extreme water temperature, salinity and light, they may expel their colored zooxanthellae and turn white (Coles & Jokiel, 1978). As the corals bleach, they become brittle and more prone to disease. When conditions return to normal, corals may incorporate the zooxanthellae again and regenerate after a while (Buddemeier & Fautin, 1993). The extreme circumstances may change the zooxanthellae from beneficial symbionts into harmful parasites that need to be expelled and if, for instance by climate change, such conditions occur too often, without time for regeneration, coral bleaching becomes permanent and entire reefs will die (Baker et al., 2018).

Coral reefs are the most diverse ecosystems on earth. They are not only a wonderful underwater world of great beauty, but they protect vast stretches of coast against wave erosion and ultimately feed billions of people with hundreds of billions of dollars’ worth of seafood. Coral reefs deserve protection and we have to:

  • Learn how to diminish environmental stress for coral reefs
  • Teach corals how to deal better with their environmental stress

We ask ourselves, for improving the well-being of coral hosts and their symbiotic guests, what bio-geochemical technology is best to use?

String of microbially precipitated nano crystals of magnetic iron oxides within the elongated cell of a magnetotactic bacteria

What is going on between minerals, metals and microbes in bio-geochemical technology?

By using minerals in bio-geochemical technology, we can influence the interaction between microbes and metals, to improve environmental management.

The health of soil and water can be managed through the interaction between microbes and metals, using minerals in bio-geochemical technology. Microbes (bacteria, fungi and algae) influence metal concentrations when deteriorating rock and minerals during bio-weathering and when forming, directly or indirectly, minerals during bio-mineralization (Gadd, 2010).

This interaction between minerals, microbes and metals determines the availability of life sustaining resources and life-threatening toxins that regulate the natural habitat of the critical zone or biosphere; the near-surface environment of rock, soil, water and air, home to living organisms.

Microbes concentrate the essential nutrients from mineral surfaces (Vaughan et al, 2002); i.e. carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur that form 95% of the biomass and other elements with essential biochemical and structural functions such as K, Ca, Mg, B, Cl, Fe, Mn, Zn, Cu, Mo, Ni, Co, Se, Na and Si. Microbes and minerals also control the concentrations and bio-availability of thirteen trace metals and metalloids that are considered priority pollutants i.e. Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Se, Tl and Zn (Sparks, 2005).

Many examples show how microbes interacting with metals may operate in environmental management. For instance, microbial metal mobilization through bio-leaching can be used for metal recovery, recycling and bioremediation of mineral waste and contaminated soil (White et al, 1998). Microbes can be used to immobilize metals by bio-precipitation, for decrease of toxic concentration in bio-available phases. Reduced metal(loid)s like Se(0), Cr(III), Tc(IV) and U(IV) form insoluble precipitates through reduction in anaerobic processes. Single-oxidation-state metals are immobilized during precipitation with biologically produced sulfide and phosphate. Immobilization through microbial biosorption occurs by physico-chemical binding of metals on dead and living walls of microscopically small cells that expose a very high surface per weight to the metal containing solution. Biominerals such as microbial nano crystals of magnetic iron oxides precipitated by magnetotactic bacteria can be used for sorption of metals and their recovery from solution by magnetic separation.

For practical use of microbes and minerals in environmental management we have to ask: How can microbes manage metals better with minerals in biogeochemical technology?