Article I wrote on Salinity

Hello All:

Attached is a copy of an article I wrote on salinity that might of interest.


Cheers,

DrTim

 

Can't read it on my phone , but I'll check it out when I get home! Thanks for the article!

 

I read it here at work.

If Seawater averages 35, then why is your range well below that, even for a reef tank- according to your article?

 

Good article. Recommend calibrating the less expensive hobby refractometers we generally use, with readily available calibration fluid (35 ppt) that is close to what we are measuring for. Helps avoid the slope error between 0 and the 35 ppt or so we are trying to obtain. Calibrating at 0 will give accuracy with RODI, but may be off at higher salinities we work with.

 

Tank you for the article. Your recommended salinitity levels seems way low though. Most references reference an average of about 35ppt. For example,
Global water masses: summary and review. Emery & Meincke 1986, shows most oceans, with a few exceptions ranging from 34-36ppt.
http://archimer.ifremer.fr/doc/00110/22090/19731.pdf


Similar results are derived in Chemical Oceanography Third edition. F. Millero 2006. ch. 2.4

Also hobby sources such as R. Shimek And R.H. Farely cite similar numbers
Aquarium Frontiers On-Line: November 1997: Feature

I am aware that rain storms and runoff can drastically lower salinity, I know there are examples of reefer getting down to 10ppt or so, short term. These however are outlier events and, without a strong logical argument to include, it seems that these should not be included in calculations. Also, I don't have cites in front of me, but As i recal, sources tend to show hypo salinity can be tolerable short term, but not so much long term, even minor changes, in the 10% range from average for extended periods may be fatal. So, recommending significantly lower levels, for reefs tanks anyway, seems a bit odd. Perhapse citations would help understand where you are coming from.

Anyway, I think overall, it is a very useful and clearly written article, although I think keeping a reef at 1.021 is likely detrimental long term. Heck even if organisms were adapted to those conditions, with aquarium salt components often calibrated to levels of 1.026, you would expect nearly a 20% decrease in important components, including of course, ca, mg, bicarbonate etc.. So, for example, if you were expecting calcium to be at 400ppm @1.026, now you would be closer to 320ppm, which in an aquarium with significant calcium usage, supplementation would need to be monitored much more closely at a minimum.

 

Hello M2434- thanks for your comments. My feeling is that if your tank has a significant amount of calcium usage you'll never keep with the calcium needs by just changing water which is why most people have a calcium reactor.

As to the potential for long-term harm to your coral at a salinity of say 32 ppt or so rather than 35 ppt studies show this not to be the case. For example, here is a link to a summary of paper studying the decline in the growth rate of Porities on the Great Barrier Reef. Declining Coral Growth - AIMS

To quote from the summary: "The study considered a range of factors known to determine coral growth and calcification including competition for space, water quality, salinity, diseases, irradiance, currents, large-scale and long-term oceanographic oscillations, temperature stress, sea surface temperature and ocean acidification.All but the last two, both attributable to rising atmospheric CO2, were excluded as being likely causes of the observed decline."


Best

DrTim

 

vtecintegra - I am not a fan of one point calibrations. Whether you calibrate at 0 or 35 when using a one point calibration you can generate significant slope error. It all depends on how accurate you want to be. For better accuracy you should do a two point calibration and check a known inside the calibration points.

 

great article! really nice explanation of salinity and how it came to be used as a unit of measure. I can agree with the salinity of 1.021 to 1.024 being appropriate for coral taking into consideration that the ratios of the different elements are considered a constant as per your article. Maybe we use higher salinity in our reef tanks to more easily obtain the correct ratios of elements in the water than the actual effect it has on the survivability of coral.

 

Thanks, I will take a look at the link. Water changes do not provide the necessary ca and alk, but they do provide the set-point. If my setpoint is higher and my ca-reactor malfunctions, it buys me a few more days if I don't notice right away.

As for hyposalinty, I haven't looked at this recently, but have in the past. As I recall, there is data to confirm that corals do indeed show signs of stress and increased mortality at lower salinity levels. It seems I have a few better articles saved somewhere if I can find them, but the following articles seem to also mostly agree. While in nature, corals may tolerate stress better, there is likely a larger accumulation of stressors in our systems. So, I would guess that there is somewhat less tolerance in captivity. More anecdotally, over the years, on the forums, I have seen a fairly large number of instances where hobbyists have raised their salinity levels and seen noticeable improvements.

So, for example, while Berkelmans may find that acropora may tolerate 22-28 psu, the others I believe show that there is still stress occurring before mortality. So, for example, again in Berkelmans after 13 days at 26psu there was mortality, so, then at what level was there stress? And what happens when there are other stressors, does that increase mortality sooner, or at higher psu? I think there is at a minimum a stronger argument to leave salinity closer to a typical 35 ppt, but that is my opinion and I don't mean to go off on a tangent, so, I can leave it at that for here. I do feel long term there is not any great reason to keep corals at levels other than 35ppm and especially not less than approx. 32ppm and is undesirable to do so, based on anecdotal as well as empirical evidence. Agreement isn't required though


Salinity thresholds of Acropora spp. on the Great Barrier Reef

Berkelmans et al. 2012

Abstract Salinity tolerances of reef corals have been
experimentally investigated since the early twentieth century.
Yet, nearly 100 years later, we are no closer to having
a threshold that can be applied in studies of the impacts of
freshwater runoff on coral communities. We present an
empirically derived salinity threshold for sensitive Acropora
species from the Keppel Islands in the southern
inshore Great Barrier Reef (GBR), based on in situ salinity
exposure and coral responses during a major flood event in
2010–2011. This threshold is presented as a dose-time
response for a salinity-sensitive range of 22–28 PSU and
an exposure time of 3–16 days at the lowest and highest
salinities, respectively. The robustness of the salinity
threshold was confirmed by comparison with responses of
corals to low salinity *600 km north in the central GBR,
which were exposed to substantially different turbidity and
chlorophyll levels during the period of hypo-salinity.

Exploring the effect of salinity changes on the levels of Hsp60 in the tropical coral Seriatopora caliendrum

Seveso

Abstract
Osmotic stress represents a limiting physical parameter for marine organisms and especially for sessile scleractinian corals which are known to be basically stenohaline and osmoconformers. The salinity changes may cause important cellular damage since corals lack any developed physiological regulatory system. One mechanism of reaction to deleterious conditions is the rapid increase of the induction of heat shock proteins. This study highlights the modulation of the expression of a mitochondrial heat shock protein, such as the chaperonin Hsp60, in the animal tissues of the scleractinian coral Seriatopora caliendrum under three salinity scenarios (hypersalinity of 45 ppt, hyposalinity of 25 ppt and extreme hyposalinity of 15 ppt). The study was performed during the time course of a 2-day period and accompanied also by the assessment of the coral health condition. For each salinity stress S. caliendrum responds differently at the morphological and cellular levels, since the Hsp60 exhibited specific patterns of expression and the coral showed different tissue appearance. Furthermore, the response reflects the severity and exposure length of the disturbance. However, the results indicate that S. caliendrum seems able to tolerates high salinity better than low salinity. In particular, in extreme hyposalinity conditions, a considerable gradual down-regulation of Hsp60 was detected accompanied by necrosis and degradation of the coral tissues. The study suggests that Hsp60 may be involved in the mechanisms of cellular response to stress caused by exposure to adverse salinity.


Cellular pathology and histopathology of hypo-salinity exposure on the coral Stylophora pistillata

Downs et al.

Abstract
Coral reefs can experience extreme salinity changes, particularly hypo-salinity, as a result of storms, heavy rainy seasons (e.g., monsoons), and coastal runoff. Field and laboratory observations have documented that corals exposed to hypo-saline conditions can undergo extensive bleaching and mortality. There is controversy in the literature as to whether hypo-saline conditions induce a pathological response in corals, and if there is a relationship between decreasing salinity treatment and pathological responses. To test the hypothesis that hypo-salinity exposure does not have a pathological effect on coral, we used histological and cellular diagnostic methods to characterize the pathology in hypo-salinity-exposed corals. Colonies of Stylophora pistillata were exposed to five salinity concentrations [39 parts per thousand (ppt), 32 ppt, 28 ppt, 24 ppt, and 20 ppt] that may realistically occur on a reef. Histological examination indicated an increasing severity of pathomorphologies associated with decreasing salinity, including increased tissue swelling, degradation and loss of zooxanthellae, and tissue necrosis. Pulse-amplitude modulated chlorophyll fluorimetry kinetics demonstrated a decreasing photosynthetic efficiency with decreasing salinity conditions. Cytochrome P450 levels were affected by even slight changes in salinity concentration suggesting that detoxification pathways, as well as several endocrine pathways, may be adversely affected. Finally, these studies demonstrated that hypo-saline conditions can induce an oxidative-stress response in both the host and in its algal symbiont, and in so doing, may synergistically increase oxidative-stress burdens. As with other types of environmental stresses, exposure to hypo-saline conditions may have long-term consequences on coral physiology.