Coral Cohabiters: Time for a Status Update?

Coral Cohabiters: Time for a Status Update?

Symbiosis derives from the terms sym for together, and biosis for life. The coral reef appears to be a poster child for a lifetime of togetherness. The soft tissues of coral polyps are embedded with hundreds of single-celled, free-swimming dinoflagellates, captured from nutrient poor, crystal clear tropical waters. Photosynthesis by dinoflagellates provides 95% of the organic food used by the polyps. In return, the dinoflagellates are housed in a safe environment where their hosts supply them with carbon dioxide and minerals needed for photosynthesis. 

Friends with Benefits: Like a Facebook status, the relationship of coral symbionts is complicated. Clearly, the coral benefits: oxygen and sugars produced by trapped dinoflagellates enable these corals to grow as much as three times faster as those without symbionts. But the converse is not true: in the symbiotic relationship, it takes ~70 days for the dinoflagellates to double, in contrast to a mere 3 days outside the coral. So symbiosis has a fitness cost for the algae. In reality, the coral host is more like an active farmer, who lures and engulfs the free-living dinoflagellates into captive domestication. When the coral is stressed, it loses control of the delicate energy balance in this relationship and expels its colorful guests en masse. Coral bleaching devastates the entire reef ecology and is a symptom of climate change which brings warmer, more acidic, nitrogen rich waters.

● All relationships lie along a continuum: from truly mutualistic, where both partners benefit and the success of one is tied to the success of the other, to commensalism, where one partner benefits but the other is neither harmed nor helped, and the extreme cases of parasitism, in which one organism exploits and harms the other. Isn’t there a parallel with human relationships as well? 

The more we learn about the diversity of life and the structure of genomes, the more it appears that much of the evolution of biodiversity is about the manipulation of other species—to gain resources and, in turn, to avoid being manipulated (John Thompson, 1999). True mutualism may be rare in nature. Evolutionary selection tends to maximize individual fitness and conflict of interests are inevitable!

REF: Is the coral-algae symbiosis really ‘mutually beneficial’ for the partners? S.A. Wooldridge (2010) Bioessays 32: 615-625

IMAGES: Check out more stunning coral photographs by Daniel Stoupin at


This entry was posted in Rajini Rao and tagged . Bookmark the permalink.

61 Responses to Coral Cohabiters: Time for a Status Update?

  1. rare avis says:

    Good morning, Rajini!

    Very interesting! Thank you, I’m sharing, too 😉

    I have a quick question, if you have a sec?

    I just read yesterday about a type of soil bacteria… Individual bacterium ‘lend’ their ‘sisters’ material to repair cell walls, without harming themselves. They seem to prioritize the health of the entire population, helping each other out, as it then benefits each individual.

    I likened it to a sort of: ‘Eusocial Altruism’; a sort of ‘hive like’ mentality, tho there was no evidence of any single bacteria sacrificing itself for the benefit of the population as a whole, like an ant might do.

    Would that particular strain of bacteria be considered “mutualistic”?

    Thank you! 😉

  2. Rajini Rao says:

    rare avis good morning! The story of soil bacteria collaborating in cell wall repair is intriguing! Do you have a link so that I may “dig in” some more? Altruism is yet another relationship arrangement. There’s even altruistic suicide among cells, called programmed cell death or apoptosis, where cells die “neatly” as part of an organism’s development. 

  3.  Isn’t there a parallel with human relationships as well? // of course, so true!

  4. Rajini Rao says:

    As I wrote this, I found myself pondering human relationships as well Vasudevan Tirumurti 🙂

  5. :-))) yes, but it is even more complicated than the simpler equations of these!

  6. rare avis says:

    Here is the article!

    “a certain type of soil bacteria can use their social behavior of outer membrane exchange to repair damaged cells and improve the fitness of the bacteria population as a whole, new research demonstrates. This is the first evidence that a bacterium can use cell-content sharing to repair damaged siblings, the authors say.”

    Thank you, Rajini!

    Yes, I know a little bit about true ‘altruism’, I think my characterization was a bit more tongue-in-cheek: something I shouldn’t do, when discussing science! 😉

    But I am very curious about these guys! 😉

  7. Rajini Rao says:

    Thanks, rare avis . I’ll check out the PNAS paper. It looks like the authors are making the case for primitive signs of multicellularity in these types of bacteria. Living together entails compromise and caring, much as in social constructs of people 🙂

  8. rare avis says:

    Rajini Rao

     Thanks! I’d love to hear anything you learn, or conclude…

    I thought it was fascinating!

  9. Always fascinating Rajini Rao 

  10. Chad Haney says:

    Nice post Rajini Rao. I was happy to find Daniel Stoupin via #ScienceSunday . He has some amazing photos and explains them well. The timing of your post is a bit funny because I just read about the ~40 year-old failed artificial tire reef in Florida. Were we really that crazy back then to think that tires would be a good artificial reef?

  11. Rajini Rao says:

    Chad Haney I wish Daniel Stoupin would post more frequently to G+. We’re all fans! 

    I’d hate to think of ugly rubber tires in tropical oceans..yikes! It’s bad enough that they are shredded into playground mulch- where I hope they don’t leach chemicals or clog up drains. 

  12. Rajini Rao says:

    I’d bet anemone that some reefer was involved in that infamous incident, Peter Lindelauf .

  13. Chad Haney says:

    Shredding them and putting them into running tracks seems to be sensible but I don’t know if they still do that.

  14. Very interesting read. The only coral I have touched are the ones(some types) when dead, that are used for making beads and jewelry. 

    Love what you said in the last two paragraphs, tickled my philosophical side into a monologue :). 

  15. Rajini Rao says:

    Rashmi Pahuja I have been experimenting with including something tangential to the science in these posts to interest a broader audience. Glad you enjoyed the read and don’t hesitate to share your monologue! 🙂 

  16. Chad Haney I’m surprised that the effort failed. There are many square miles of empty sand bottom out there. Blank, featureless.

    Drop a “cinder block” on the bottom and go back in a week, and you will find something has moved in. Go back in a year and find it colored with encrusting sponge and coraline alga. 50 years later and you couldn’t recognize the original object.

    The simple seed of a three dimentional object in a desert of sand provides a stable platform for attachment and shelter – and life will continue to build on it.

    Many reef creatures including corals have a free swimming stage in their development as offspring are launched into the current, and need only a toehold to flourish.

    A coral reef is a wonder of diversity, and the real estate is precious. Every square inch of a healthy reef is occupied and contested.

    The practice of sinking old ships on sand flats provides a stable platform for reef creatures, and has been successful from my experience.

    Many ancient shipwrecks are spot reefs that have long ago consumed the vessel.

    Frankly I am surprised there is any surface that wouldn’t serve as a base, there must be something chemically repulsive about tires… too bad.

    Rajini, great post on symbiosis!

    The parallel behavior we recognize in human society is an interesting point. Apparently a common evolutionary adaptation in the struggle to survive.

    Thank you for your valuable time and an enlightening perspective. 🙂

  17. Rajini Rao says:

    Good point about seeding the ocean floor with scaffolding, David Andrews . They must have “seeded” the structure with organisms too. When I read about coral bleaching, I wondered if there were efforts to repopulate them with zoozanthellae (the dinoflagellates): these are so plentiful in the ocean, essentially a component of plankton. Perhaps the sheer magnitude of coral bleaching makes this a difficult task. 

  18. Chad Haney says:

    David Andrews​, I’ve seen concrete objects work quite well for artificial reefs. I think tires are not durable enough and likely have some chemical components that prevented a reef from forming. Maybe Sam Andrews​ knows the details why tires don’t work but concrete does.

  19. AHMED SAVANI says:

    Rajini Rao This is something tickles my neocortex. Really your post are awesome & worthfull.

  20. Rajini Rao says:

    AHMED SAVANI thank you! Your comment brought on a burst of dopamine 🙂

  21. Rajini Rao Great post. Adding the  question of a correlation with human relationships stirs a readers cognitive thought processes.  

    Although the definition of symbiosis is basically limited to organisms and relationships, groups, if taken in its pure fundamental form;  a beneficial relationship,then it could refer to other types that may include matter and energy. There is a hint of this in many philosophical and religious ideology. Ex: yin yang. Food for thought. 🙂     

  22. Rajini Rao says:

    Garron Longfield that’s an interesting extension, thank you for the idea! 

  23. Jim Gorycki says:

    This is an excellent topic. My son just took his marine science 2 honors final — that was on his review — about coral cohabitation. Also about temperature and acidity changes in the water stressing the coral. Thanks!

  24. Rajini Rao says:

    Jim Gorycki in that case, your son probably knows a great deal more about this than I do! 🙂

  25. I think the spectrum of relationships from mutualtistic to parasitic reflect human relationships, but not always in the dating/cohabiting sense that originally popped into my head.

    It seems to apply to labor relationships just as much. The nice thing about professional jobs is that you sometimes find yourself in a situation where your rewards grow with your work. There’s a bonus if we get this product out on time or a promotion if you excel on a particular project. In some lower-scale jobs, there’s often no real correlation between your effort and your rewards. Your pay isn’t going to change much, no matter how hard you work.

    Maybe the study of biological relationships will lead to better working relationships for people, because we’ll have a better understanding of how the labor and benefits are divided.

  26. Rajini Rao says:

    Another excellent analogy, thank you J Bennett ! As a thesis advisor/mentor I think of my relationship with students as mutually beneficial- they get their degree and I get to share in their research efforts. Our success is tied together. 

  27. Rajini Rao I did an excellent analogy? Woohoo! Another screenshot for my portfolio of occasional episodes of lucidity! 😉

  28. Rajini Rao says:

    Speculation is a step towards sapience, J Bennett (The Speculating Ape) 🙂 

  29. Rajini Rao says:

    Or should I say sapiens as in H. sapiens 🙂

  30. Rajini Rao Homo semisapiens redneckus is probably the most accurate classification for me. I’ll keep evolving and we’ll see how it works out.

  31. Fabulous post….explains similar behavior to human beings…if I am right ?

  32. Rajini Rao says:

    The terms of symbiosis, mutualism and parasitism are not conventionally used to describe human relationships but we have been having fun speculating on similar behavior in humans 🙂

  33. Thank you…..and great work 🙂

  34. Rajini Rao says:

    rare avis here is what I found out about the soil bacterium that caught your interest: Myxobacteria have been studied for over 50 years for their social behavior. They form swarms, move forwards and backwards along slime trails, and cluster into fruiting bodies under stressful conditions. Their behavior resembles slime molds, which are eukaryotic fungi, yet these bacteria are much simpler prokaryotes! One benefit to their “social behavior” is that they feed by secreting digestive enzymes that breakdown organic stuff in soil and bark of trees. These enzymes concentrate in the swarms so that the digestion is more efficient and benefits everyone. Unlike a typical bacterial colony that forms a defined dome on agar plates with neat edges, a colony of myxobacteria looks like an over easy fried egg 🙂 At the boundaries, bacteria glide away in rafts and long lines, to find new food material.

    The paper that your ScienceDaily article referred to is part of a series of ongoing studies that detail how these bacteria collaborate for mutual benefit of the colony. These primitive behaviors help us understand how multicellular organisms evolved: for example, adjacent cells in an epithelium communicate and pass nutrients or electrical/chemical signals, although by very different proteins, unrelated to bacterial ones.

    Hope this addressed some of your curiosity! I’m attaching a link to a free review and you may enjoy looking at some of the figures:    

  35. Chad Haney David Andrews  I’ll keep this brief(ish) so not to hijack Rajini Rao  excellent post. I’m not an expert on artificial reefs, but I have read some studies on them. 

    The Osborne reef was constructed from tyres clipped together with nylon and steel.  Unfortunately these broke down and the structure shifted – especially during storms/hurricanes that frequent Florida  This caused a few issues.  Sessile organisms that settled on the tyres may have been dislodged/killed, and the tyres themselves caused damage to natural habitats (especially reefs), and also washed up on the shoreline (an eyesore for beach-goers).  Their removal began in 2001.

    The type and amount of toxins leached from the tyres to biota from tyres can vary depending on 1) the tyres themselves and 2) where the tyres are placed (degradation may be slowed down, particuarly placed in cool, low-light (low-uv) settings).  Some studies have found sessile organisms on tyres have elevated concentrations compounds that are used in tyre construction.  I’ve not come across anything that talks about the impact of those elevated levels to the organisms.

    Settlement of sessile organisms (inc plants) can vary depending on the environmental conditions in the area the reef is placed, the species that settle, and also set-up of the reef (which can infulence  suitability of habitat).  This goes for any material used for reefs – not just rubber.  

    Hope that helps!

  36. Rajini Rao says:

    Thank you, Sam Andrews . That was really informative. It does seem like concrete-like materials would be better and heavier for anchoring new reefs. 

  37. I think concrete offers more options… you can change the shape, texture, even add other materials (eg rock) to it to provide habitat… but I’d like to just pop this quote here from two researchers who have been looking at artificial reefs for a while – Alistair Edwards Edgardo Gomez:

    “There are estimated to be in excess of 500,000 “reef balls” of varying size deployed worldwide. These will provide at most a couple of square kilometres of topographically complex substrata as a cost of US$ tens of millions. There are an estimated 300,000 km2 of shallow coral reefs in the world, so there is plenty of substrate available. The main problem is that much of it is poorly managed or degraded”

  38. Chad Haney says:

    Thanks Sam Andrews​. I figured that you would have more insight.

  39. Rajini Rao says:

    Would love to learn more about the ecology of coral reefs, Sam Andrews 🙂

  40. Rajini Rao​, regarding zoozanthellae, it is my understanding that elevated temperature is the main reason corals expell their guests. I’m not sure the corals would be receptive to repopulating under that stress.

    It is my assumption that given favorable conditions, corals would correct the deficit in short order, considering they are a ubiquitous component of the environment.

    Enlighten us Sam Andrews​?

    Sam, you are a welcome addition to my science circle, privilaged to meet you. 🙂

  41. Jim Gorycki says:

    Rajini Rao besides acidification and bleaching there are tons of reefs being killed by being smothered with sand and construction debris. We’re noticing this happening in the keys. Jimmy buffet warned us about years ago

  42. David Andrews​ there are a few hypotheses on why corals lose their zooxanthellae, such as ,but thermal stress seems to be the main driver behind widespread coral bleaching events.  One line of thought is that the elevated temperature hampers the photosynthetic ability of some zooxanthellae species.  Without photosynthesis, they provide the coral with no benefit so they either leave or are expelled (the exact mechanisms are still under study).

    Other research has found that corals that take on more thermally-tolerant zooxanthellae are more resistant to bleaching, and some of those algae species are generalists  – they can live in a variety of different host coral species.  We don’t know how widespread these algae with higher thermal tolerance are though.

    As for corals correcting the algae deficit after stress… yes this can happen, but as long as the stressor is diminished prior to the corals dying (they can survive a limited time without zooxanthellae) .

    And thanks for the compliment! Glad to be ‘on board’ :)

  43. wonder full castume

  44. Sam Andrews Thank you 🙂

  45. Marta Rauch says:

    Thank you Rajini Rao​

  46. 連盈貴 says:


  47. So fascinating and amazing beautiful…

    Many Thanks for Sharing!

    xxx xxx xxx

  48. life always finds a way, they say..

  49. Hola soy de Concordia entre ríos ok soy Leandro ok están muy bueno el vídeo ok

  50. Very beautiful location are there in youer life

  51. daniel wyatt says:

    the release of the algae must contribute to some degree to the free nitrogen..dying algae?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s