It is quite strange to find corals growing at abyssal depths. Are they there because there is rock (a firm substrate) or because there are abundant nutrients, e.g., food? In the paper, your findings suggest that the corals can record hydrothermal events as they are imprinted somehow in their exoskeletons. However, you do not mention that they can be benefiting from the hydrothermal fluids and bacterial production at the vents - why not? Is the question difficult to answer? Or, is it not of any interest? Are there more corals growing on the west or on the east side of the Mid Atlantic Ridge?
Article Mid-Atlantic Ridge hydrothermal events recorded by deep-sea corals
If these deep-water corals are scleractinians, there are many species that do not need a firm substrate because they are free-living. I could not access the paper by Smith et al. (1999) to see which coral species were studied.
Corals are common at these depths, which are not abyssal, and those requiring hard substrate to settle do so preferentially at sites with stronger current flow. In soft sediment areas, such as the Northern Gulf of California, vent fluids cause sediment cementation with carbonates or barytes and corals are found only around the vents because suitable substrate for settlement is not present elsewhere. At non-abyssal depths there is no evidence that bacteria from vents or seeps are necessary to support the corals, although they may well benefit from additional food sources. Note that fluid flows from vents and seeps can generate increased bottom currents and these can cause greater coral settlement/survival.
(Hi Martin.) These particular corals were pretty far from any actual zone of biological productivity-obviously, close enough to pick up trace elements, but...unlikely to have garnered any nutritive advantage.
But this raises the larger question: how would one tell??? We only had the hard parts, and if this is the case, then I guess one could go after the 13C signals, using the correction factors proposed by Heikoop et al (GCA 2000). Grottoli has also done some recent work along these lines.
If soft tissue were available, then a panoply of possibilities opens out, all the way from basic metabolic-balance studies to immunological work to see if the corals were ingesting vent bacteria.
in fact thank you to attract my attention to this paper. It is a quite nice and neat note but the abstract was written in such a way that it does not really catchy. But it was long time ago, the paper is dated 1999 (and I would encourage the author to change the date in the researchgate reference).
The interesting thing is that there was no hydrothermal activity recorded in the area at MAR 45N that time and Desmophyllum skeleton was used as a proxy for prediction of the hydrothermal site - because of high concentration of metals. And what is more interesting that in 2011 in JC24 the site that mow called Moytirra was visually confirmed.
http://www.interridge.org/irvents/content/mar-45-n
and in fact it is an answer to the question ‘Why bother about..?’ and from this point the paper is quite neat.
as about the second question.. for my experience such high concentration of metals will apparently cause mortality..
it is not clear if these were alive or dead skeletons and also... if they were long time dead and accumulated the metals because of porosity.
for West and East try this paper
Cairns SD, Chapman RE. 2001. Biogeographic afnities of the North Atlantic deep-water Scleractinia. In: Willison JHM, et al., editors. Proceedings of the First International Symposium on Deep-sea Corals. Ecology Action Centre and Nova
Scotia Museum, Halifax, Nova Scotia. p 30-57.
Thanks for your very informative and interesting answer, Tina.
However, these filterfeeding organisms that evidently record the nearby hydrothermal venting in their skeletons, feed on organic particles, mainly forams and other secondary trophic organisms that feed on the primary producers (bacteria / archae) that we know abound from the fluids and nutrients coming out of the vents. Even though many of the inorganic particles can be toxic, the filterfeeders survive.
We have similar conditions for deep-water Coral reefs, please see my book on this subject of 2008, here:
https://www.researchgate.net/publication/258515003_Deep-Water_Coral_Reefs._Unique_Biodiversity_Hot-Spots
Book Deep-Water Coral Reefs. Unique Biodiversity Hot-Spots
Desmophyllum cannot be considered as a filterfeeder... it is quite planktivorous with preference > 1 mm, may be not exclusively but with high percentage of plankton in the diet and it is really capable of catching alive animals.
Do not underestimate them.
https://www.google.ru/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCsQFjABahUKEwjno_Dx5unIAhUG_nIKHdboCpw&url=http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F230735523_Trophic_relationships_in_a_deep_Mediterranean_cold-water_coral_bank_(Santa_Maria_di_Leuca_Ionian_Sea)&usg=AFQjCNGKAVC7AahJdozkLqUYt-NcnVDU2g
http://epic.awi.de/25994/1/Diplomarbeit_SS_klein.pdf
I agree, Tina, but also plankton needs nutrients - I guess some of the food is zooplankton and may have its origin close to the bottom if there is any nutrients around to support them?
And, when it comes to the low-pH of the Comau Fjord in northern Chile, it is well-known to many, that there are diffusive volcanic seeps through the bottom of that fjord, not far from where the studied shallow water (cryptic) corals are growing. Please take a look at the attached report:
https://www.researchgate.net/publication/283047632_OCEAN_pH-VARIATIONS_CORALS_AND_THE_OFFSHORE_PETROLEUM_INDUSTRY
Technical Report OCEAN pH-VARIATIONS, CORALS, AND THE OFFSHORE PETROLEUM INDUSTRY
you are trying to compare apples and oranges.. I mean seeps and vents. it is not the same.
Sorry, I do not understand your point about criticizing that particular paper for do not bring up the question they were not interesting and not able to raise because all they had were several dead corals from dredge samples.
Ok, Tina, sorry for that,
I thought perhaps, there was more information than only some dredged samples.
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