Effects of low salinity on corals?

[jsker]

Hi @jsker , with regards your original question with reference to your title Effects of low salinity on corals?

Very interesting topic. One which triggered my own inquisitive nature. I had a browse through some research papers on the subject. The information I have read would suggest that low salinity (Hypo Osmosis) can indeed have a negative effect on corals and in some cases induce a bleaching effect. The data would suggest that, it is the symbiont relationship that is most affected. The observations appeared to show that the efficiency of the symbiants ability to photosynthesise and provide nutrition to its host is reduced by a significant factor.

However at least one paper, contrary to previous conclusions, suggest that the effects can be classed as sub lethal. (Experiments carried out in closed systems, salinity levels varied between 37ppt control and 33.5ppt - 15ppt to monitor response)

With regards my comments, I must include two significant caveats.

1. I am by no means academically qualified. Therefore my comprehension and any conclusions are based solely as a hobbyist.

2. My experience of comparing observations and conclusions from Oceanographers / Marine Biologists and Aquarists / Hobbyists would appear to show a number of conflicting views. For instance in the wild corals can be found to thrive in a wide range of temps and salinities. These can include tidal pools, lagoons and areas susceptible to wide variations in environmental conditions. Where as aquarists we would generally experience very high mortality if we maintained our aquaria under such extreme conditions.

I would therefore strongly suggest that anyone seriously interested in the topic should carefully read through the data before making any definite conclusions. For that reason I have included a link to the paper In question. If you have any academic association then the full paper should be available through your logon. For those without access, the full abstract should still be available to read.

https://www.researchgate.net/public...a_Nature_and_cause_of_'low-salinity_bleaching'

Note to admin please advise if posting links of this nature is not allowed. Thanks.

Tony, goodstuff

When doing my search I came across links and bits of information, as you are suggesting there is really no definitive answer and like yourself my curiosity was triggered.

 

[Tony Thompson]

I would add two comments to that discussion of this paper:

1. They didn't do anything to slowly acclimate the corals to different salinities (or if they did, I missed it).

2. They lowered salinity by seawater dilution, so everything dropped similarly, and nothing was maintained at natural levels (calcum, alk, potassium, etc. ).

Doing 1 or 2 differently might have led to different results.

Hi @Randy Holmes-Farley , and @jsker I take your point about my post not detailing the specific controls placed on the observations. I think my aim was to highlight the effects that low salinity levels may have with respect to osmosis and what biological effects this could have on the coral.

The particular paper I referenced, was part of a number of other papers that I consulted. Unfortunately I felt that a more concise list of links may not have been appropriate for the forum, reason, my note to admin. I also find it quite fascinating how academic observations vary and sometimes conflict with those of hobbyists. "One of the reasons I love this hobby".

For a further review and supporting material I have included the citations below.


Citation from: Effects of hypo-osmosis on the coral Stylophora pistillata: nature and cause of ‘low-salinity bleaching’ Ailsa P. Kerswell , Ross J. Jones, Centre for Marine Studies, The University of Queensland, St Lucia, Queensland 4072, Australia

"Corals are osmoconformers, rapidly absorbing water to be come iso-osmotic with their sur- roundings (Rankin & Daven port 1981), which can cause tissue swelling, tissue necrosis, and the induction of an oxidative-stress response that is visible with histology in some species (Downs & KramarskyWinter 2009). Hypo salinity can also disrupt symbiosis with Symbiodinium (Muthiga & Szmant 1987, Coles & Jokiel 1992, Kerswell & Jones 2003 leading to the production of damaging reactive oxygen species that begin apoptotic and/or necrotic pathways ( Tchernov et al. 2011). Damage at the cellular level from these processes could have aided bacterial invasion of tissues."

Best wishes from across the pond.

 

[Randy Holmes-Farley]

Thanks.

"Corals are osmoconformers, rapidly absorbing water to be come iso-osmotic with their sur- roundings (Rankin & Daven port 1981), which can cause tissue swelling, tissue necrosis, and the induction of an oxidative-stress response that is visible with histology in some species (Downs & KramarskyWinter 2009). Hypo salinity can also disrupt symbiosis with Symbiodinium (Muthiga & Szmant 1987, Coles & Jokiel 1992, Kerswell & Jones 2003 leading to the production of damaging reactive oxygen species that begin apoptotic and/or necrotic pathways ( Tchernov et al. 2011). Damage at the cellular level from these processes could have aided bacterial invasion of tissues."

Exactly the reason that very slow acclimation would be highly desirable if you intend to change salinity and see what the long term effect of lower salinity is, as opposed to what the change in salinity might cause.

This paper suggests that moving corals from one natural reef to another is a big problem, so interpretation of what caused a problem is not trivial:

https://web.whoi.edu/cohen/wp-content/uploads/sites/52/2017/04/2017_Barkley_JEMBE.pdf

"However, corals collected from one reef and then transplanted to the other had very low growth rates and very high mortality over the same time period, with only a small number of individuals alive at the end of the experiment."

 

[Tony Thompson]

Thanks.



Exactly the reason that very slow acclimation would be highly desirable if you intend to change salinity and see what the long term effect of lower salinity is, as opposed to what the change in salinity might cause.

This paper suggests that moving corals from one natural reef to another is a big problem, so interpretation of what caused a problem is not trivial:

https://web.whoi.edu/cohen/wp-content/uploads/sites/52/2017/04/2017_Barkley_JEMBE.pdf

"However, corals collected from one reef and then transplanted to the other had very low growth rates and very high mortality over the same time period, with only a small number of individuals alive at the end of the experiment."

Thanks for the link Randy, something for me to read after dinner.

I have not completed reading all the other papers, I was distracted by some interesting action in my Pico Reef, My Ricordea Yuma seems to be devouring one of my female Thor Shrimp. I had only just recently observed the same shrimp feeding off the Ric. .

I will take your advice and pay close attention to the preparation procedures mentioned in the paper, prior to data collection.

Cheers.

 

[jsker]

Thank you guys @Tony Thompson and @Randy Holmes-Farley

 

[prfishgirl]

I did a search on this topic and did not find this question of R2R

I started a auto water change on 4/15 and also recalibrated my conductivity probe about the same time. The reason for the recalibration was that for the past two years the probe was reading correctly and the last two month it has been creeping up ever so slightly. I cleaned the probe and did the calibration. I have a inexpensive refractometer and it has always read lower then than what my salinity really is so it was alway a mystery if my salinity was correct.

I will know for sure later this week, since I ordered a Hanna hi96822 digital.

My coral have been pailing but my arco's are going strong.

I am going to start raising my salinity slowly using the inexpensive refractometer and then use the new toy from now on for weekly checks.

Anyone else have this issue? please feel free to discuss this so the information will be here on R2R

Yes I have an issue just like that thought my refractometer was calibrated correctly just a month or so ago and bam I’m low.. so now I will calibrate every time before testing and I will get a Hanna salinity checker