Hello again - Welcome back to LuxeSci, a podcast to re-ignite your wonder by exploring the science behind luxury items. This week we are continuing our deep dive into the sea to talk about coral.
Dimos - what is something you wonder about coral?
Alexis - I was wondering if there a specific type of coral that can be made into jewelry.
It’s finally feeling like summer here in the Pacific Northwest. We got there a little later than everyone else (there was snow in the mountains just a few weeks ago) and what say summer like the beach. I distinctly remember going to the beach as a kid and wondering around the tidal pools looking at all the sea life. My mom trained as a scientist, including some courses in marine biology so she was a wealth of information about what we found in those pools. I really think that those shore excursions helped to spark my curiosity and wonder and led me down the path of becoming a scientist.
Dimos - what are your experiences with coral?
Background:
Corals are marine invertebrates (no spinal cords) in the class Anthozoa, Phylum Cnidaria
For those of you, who like me, last had biological classification at some point in school, biological taxonomy goes by category. The categories go from most general to most specific and they are:
Domain
Bacteria, Archaea, Protozoa, Fungi, Plant, Animal, etc
Kingdom
Phylum
Cnidaria - includes soft-bodied stinging animals such as corals and anemones and jellyfish
Class
Anthozoa - corals, anemones, sea pens and sea fans
10 orders and thousands of species
Order
Family
Genus
Species
Genus and species is what most scientist use when identifying life, for example Homo sapiens (genus Homo, species: sapien). If you’re a gardener or bird watcher, etc then you would be used to the so-called scientific name of an organism, which is the genus and the species
Coral groups are called colonies and usually consist of genetically identical polyps
Each polyp is a sac-like animal with a set of tentacles around a central mouth
Each polyp also excretes an exoskeleton
They can breed by sexual or asexual replication
Many corals rely on photosynthetic dinoflagellates (unicellular organisms) for their nutrients. These are referred to as zooxanthellae and are responsible for the coral’s color. This means that these corals are found in shallow water where the sunlight can penetrate to allow for the photosynthesis
Zooxanthellae - most are genus Symbiodium and are unicellular dinoflagellates that live in symbiosis (interaction between two different organisms living in close physical association, typically to the advantage of both) with corals, jeyllfish, and demosponges. Their photosynthesis provides their hosts with organic carbon compounds and they receive nutrients and access to sunlight in return
Fun fact: It was a French man named Jean-Andre Peyssonel who first identified corals as animals in 1726, based on studies in the Mediterranean
With so many different species of coral, what is used for jewelry? If you haven’t seen coral jewelry, it’s usually a very distinctive shade of red. This is from the genus Corallium.
These have very durable exoskeletons and red or orange-pink colors
Unlike species that grow in shallow water, these corals grow in dark environments including deep seas and caverns (10-300 meters)
These are found mainly in the Mediterranean and also in the Pacific near Japan and Taiwan
These corals grow to be about 1.5 meters in height and have the shape of leafless bushes
Slow-growing and long-living species
Can reach a height of 40-50 cm in about 200 years
As with other coral species - the skeleton is made of calcium carbonate and the red color comes from carotenoids
The red skeleton is matte but can be shined into a glossy finish and ranges in color from pale pink to deep red
It is a 3.5 on the Mohr hardness scale (which is quite soft) and so is cut into cabochons or made into beads
These organisms have been harvested since antiquity with ancient Egyptian and prehistoric European burials containing coral jewelry
There was a thriving coral trade from the Mediterranean to India in the 1st millennium
It was used previously by the Gauls for ornamentation on weapons and helmets
Once the trade East geared up, it was rarely used by the regions that produced it and to this day, it is endangered in the Mediterranean region
Greek mythology story about the origin of coral
Perseus got the head of Medusa to save Andromeda from the sea monster Cetus. After defeating Cetus, he put the head on the sand to wash his hands and when he was done he saw that Medusa’s blood had turned the seaweed into red coral (because Medusa could turn living organism into stone)
So one of the Greek words for coral is Gorgeia because Medusa was one of the three Gorgons in Greek mythology
Side note - we focus on Greek etiology on this podcast because Dimos is Greek and we acknowledge that there are so many other cultures and their usage of these materials to explore
In the Yoruba and Bini peoples of West Africa, coral is a mark of high social rank
In Islam - red coral is on eof the gems of paradise
Science
So I’m going to do the heavy lift on the science for this episode since there was more in my lane of science (biology/biomedical science)
So the first interesting scientific question about precious corals for me was, how to they survive in the deep water. As mentioned above, tropical corals have a symbiotic organism that uses photosynthesis to produce nutrients for the itself and the coral. Deep sea corals cant’ rely on that method since not enough sun penetrates down that deep
In 2015, Jack Middleburg et al published research in Science Reports on how deep water corals survive.
They fed the corals radio-labelled nitrogen and carbon to follow their metabolic pathways
They found that cold-water (deep water) corals feed on a wide range of organic resources including algae, bacteria, zooplankton, phytodetrius, etc
However, the coral had high levels of ammonium excretion, meaning that they must have ways to keep some nitrogen resources
They found a complete nitrogen cycle in the cold-water reefs that is similar to the one postulated for tropical reefs
Nitrogen cycle - cycle where nitrogen is converted into multiple chemical forms as it circulates through the atmosphere, terrestrial and marine ecosystems
Nitrogen fixation - nitrogen in the air converted to other forms (i.e. ammonium) in soil or water
Nitrification - conversion of ammonium to nitrate. Important in the sea because nitrogen is often the limiting nutrient in the ocean and nitrite is the primary form of nitrogen responsible for new production
For C they found chemoautotrophy to be a key method of carbon acquisition.
Chemoautotrophy - organisms that can derive energy from chemical reactions and synthesize all necessary organic compounds
The results indicated a symbiotic bacteria that is a chemoautotroph and contributes to the carbon flow in the coral
So basically, deep water or cold water corals have adapted some interesting strategies for ensuring that they get the nutrients they need without having to rely on photosynthesis
One of the cool aspects of coral is the CaCO3 exoskeleton that is created and is the foundation of the reefs that coral make (and how we know them visually).
That exoskeleton is produced by a process called biomineralization
Biomineralization = the process by which living organisms produce minerals often to stiffen or harden tissues (think bone growth in mammals)
The most common biominerals are phosphate and carbonate salts of calcium and are highly controlled so that they build sophisticated structures along with organic polymers such as collagen or chitin
A research group led by Nathalie Le Roy performed high-resolution mass spectrometry and transcriptome analysis (looking at all the proteins produced) to see the different types of biomineralization in different coral species
They found that they could identify where species had diverged in their evolutionary chain based on their types of biomineralization
The red corals had a biomineral that contained a high amount of magnesium and suggested that the ability to produce biominerals was independently acquired in these types of corals
Now I’m sure you’ve heard of the acidification of the oceans makes it harder for corals to survive
Cerrano et al investigated the potential impact of increased pCO2 levels in the Mediterranean in their 2013 paper in Scientific Reports
The team harvested corals from around 45 sites near the Italian sea coast
They were acclimated in the lab and then exposed to different levels of CO2
With increased ocean acidification they saw decreased polyp growth, activity and biocalcification and reduced feeding efficiencies
That’s not the only threat to corals. They have been over-extracted for many years for use in jewelry and other decorative uses
There are currently trade regulations and management plans in place to help overcome this and there are regulations that require species-specific and country of origin verification
However, with the price of a coral necklace upwards of $20K, there are bound to be poachers and those who peddle fakes
Bertalan Lendvay et developed a genetic test to forensically verify coral identity. In their 2022 paper published in Forensic Science International Genetics, they describe their test
Their Coral-ID Assay is able to assign a coral specimen into one of six taxonomic categories.
The method is minimally destructive but is limited if there is any decay of the DNA
While we’ve been talking about a lot of rare minerals, gems, etc in the past few episodes, this is one where I’m going to say that it’s far better to just not buy coral jewelry. The ecological impacts are just too great and for me its not worth it. While changing the temperature of the oceans may seem like a big endeavor, we can definitely stop buying coral
Glossary
Symbiosis - (interaction between two different organisms living in close physical association, typically to the advantage of both)
Nitrogen cycle - cycle where nitrogen is converted into multiple chemical forms as it circulates through the atmosphere, terrestrial and marine ecosystems
Chemoautotrophy - organisms that can derive energy from chemical reactions and synthesize all necessary organic compounds
Biomineralization = the process by which living organisms produce minerals often to stiffen or harden tissues (think bone growth in mammals)
Cocktail party facts
It was a French man named Jean-Andre Peyssonel who first identified corals as animals in 1726, based on studies in the Mediterranean
What species of coral is used for jewelry? Corrallium
Where does the classic red color of the coral come from? - Carotenoids
Well, my luxurious friends, you’ve spent another 20 minutes learning the cool science behind something beautiful. We hope you remember a fun cocktail party fact about these amazing creatures the next time you see some coral and we really hope you don’t buy any coral jewelry.
A very special thank you to my cohost and audio engineer Dimos. Our theme music is Harlequin Moon by Burdy. If you like us, please, please, please subscribe and rate us wherever you listen to your podcasts.
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