CHEMISTRY
AND THE AQUARIUM by RANDY HOLMES-FARLEY, Ph.D.
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in part by:
Magnesium
in Reef Aquaria
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Magnesium is the
third most abundant ion in seawater, behind sodium and chloride.
It is also intimately involved in a great many biological processes
in every living organism. Nevertheless, the only time that it
comes to the attention of most reef aquarists is when it is
suspected of causing a problem in maintaining appropriate calcium
and alkalinity.
This article on
magnesium is the first of several that delve into a variety
of issues involving magnesium and strontium. Calcium, magnesium,
and strontium are very similar chemically. So similar, in fact,
that they get in the way of each other in a variety of situations,
and that is part of the reason why these ions merit interest
by aquarists. This article details the nature of magnesium in
seawater, how it is added, measured, and removed from marine
aquaria, and how it impacts the maintenance of calcium and alkalinity.
Future articles
will cover some of these same issues for strontium, and will
also explore the delivery of these ions to aquaria in supplements
of various sorts. How much magnesium and strontium are delivered
to aquaria in limewater (kalkwasser), for example, is not at
all obvious. In fact, it almost certainly depends on exactly
how the limewater is prepared and delivered. These issues will
be addressed experimentally on the actual products that many
aquarists use.
Magnesium
in Seawater
In full strength
seawater (S=35), magnesium is present at approximately 53 mM
(mM is short for millimolar, which is a measure of the actual
number of ions present, as opposed to ppm (parts per million),
which is a measure of the mass of ions present). Only sodium
(469 mM) and chloride (546 mM) are present at higher concentration,
with sulfate (28 mM) following close behind. Magnesium is about
five times more abundant than calcium (10 mM). Magnesium is
significantly lighter than calcium, so when compared on a weight
basis, it is only about 3 times as concentrated (1285 ppm vs.
420 ppm).
Figure
1. This sally lightfoot crab probably doesn't realize that
the coralline algae that it is standing on likely has a
high magnesium content. Photo by Debi Coughlin.
One other comment
on seawater concentrations of magnesium. The magnesium content
of seawater has not been constant since the oceans formed. Specifically,
the magnesium content has often been lower, as in the late cretaceous
period. As is discussed below, the amount of magnesium getting
into calcium carbonate skeletons is a function of how much magnesium
is in the water. Consequently, the magnesium content of ancient
sediments can be significantly lower than more modern ones from
similar organisms.1 In addition to being an interesting
fact, this result may also play a role in the suitability of
certain limestone deposits in maintaining magnesium in aquaria.
For example, such limestone is sometimes used in CaCO3/CO2
reactors or as the raw material for making calcium hydroxide
(lime). If it is low in magnesium, one may find additional supplements
necessary to maintain modern seawater magnesium concentrations.
These issues will be detailed more in future articles.
Magnesium is present
in seawater as the Mg++ ion, meaning that it carries
two positive charges, just as calcium does. Most of the magnesium
is present as the free ion, with only water molecules attached
to it. It is estimated that each magnesium ion has approximately
eight water molecules tightly bound to it. That is, water molecules
that are so tightly bound that they move with it as the magnesium
ion moves through the bulk of the water. For comparison, singly
charged ions like sodium have only 3-4 tightly bound water molecules.
A small portion (about 10%) of the magnesium is present as a
soluble ion pair with sulfate (MgSO4), and much smaller
portions are paired with bicarbonate (MgHCO3+),
carbonate (MgCO3), fluoride (MgF+), borate
(MgB(OH)4+), and hydroxide (MgOH+).
While these ion
pairs comprise only a small portion of the total magnesium concentration,
they can dominate the chemistry of these other ions. An extended
discussion of these facts is beyond the scope of this article,
but is should be noted that these ion pairs can have huge impacts
on seawater chemistry. In the case of carbonate, for example,
the ion pairing to magnesium so stabilizes the carbonate that
it is present in far higher concentrations than it would be
present in the absence of magnesium. This effect, in turn, makes
seawater a much better buffer in the pH range of 8.0-8.5 than
it otherwise would be. Without this ion pairing, seawater pH
might be significantly higher, and more susceptible to diurnal
(daily) swings.
The average residence
time for a magnesium ion in seawater is on the order of tens
of millions of years. That time is substantially longer than
that for calcium (a few million years) and aluminum (100 years),
but less than sodium (about 250 million years). In a certain
sense, this is an indication of how reactive magnesium is: it
stays in seawater a long time because it's fairly unreactive,
but it does get taken out of solution through various biological
and chemical processes more readily than does sodium.
Another interesting
characteristic of ions is whether they are excluded from organisms,
actively taken up, or just “allowed” to be present.
Like two other common ions, sodium and sulfate, the relative
concentration of magnesium in organisms is approximately the
same as in seawater (not counting magnesium in skeletons). This
probably results from the fact that there is plenty of magnesium
present in seawater, and that it is used by organisms for many
purposes. Chloride, another very common ion, is actively rejected
by organisms, and most other ions are substantially concentrated.
Organisms
That Use Magnesium
In terms of the
amount of magnesium consumed, the primary use in reef aquaria
is in calcification. When calcium carbonate skeletons are deposited,
magnesium often gets into the skeleton in place of calcium.
It is not entirely clear whether this is something that organisms
“try” to control or not. Nevertheless, the amount
of magnesium entering the skeletons of different organisms varies
greatly. Table 1 shows the relative amount of calcium and magnesium
in calcium carbonate skeletons of various organisms.
Table
1. Magnesium in calcium carbonate skeletons
Organisms
Magnesium
content of skeleton (weight %)
Reference
Corals
Suborder
Asterocoeniina and Faviina
0.07
- 0.36%
2
Suborder
Fungina
0.095-1.22%
2
Fungia
actiniformis var. palawensis
0.091%
6
Suborder
Caryophylliina
0.18-0.21%
2
Suborder
Milleporina
0.12-0.53%
2
Millepora
sp.
0.12-0.53%
2
Suborder
Stolonifera
2.98-3.52%
2
Family
Tubiporidae
2.98-3.52%
2
Tubipora
rubrum
2.98-3.52%
2
Family
Dendrophylliidae
0.05%
2
Family
Porites
0.095-1.22%
2
Porites
lobata
0.40-1.22%
2
Family
Pocillopora
0.34%
2
Family
Dendrophyllia
0.05%
2
Gorgonia
Eunicella
papillosa, E. alba, E. tricoronata, and Lophogorgia flamea
Interestingly, coralline
algae that normally packs a large amount of magnesium into their
calcium carbonate deposits (>4 mole percent magnesium carbonate,
or >1% magnesium by weight) has been shown to incorporate
less magnesium when the magnesium content of the water is reduced.
The amount incorporated is directly proportional to the magnesium
concentration. Consequently, the amount of magnesium that they
consume in aquaria is dependent on the magnesium content of
the water. This effect is also likely to extend to other calcifying
organisms as well.1
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In addition to that
used in calcification, many organisms (if not all) take up magnesium
from seawater. Organisms ranging from bacteria8-10
to fish11 take up magnesium. In many cases, there
is so much magnesium in seawater that the organisms need to
spend more effort pumping back out excess magnesium than they
do trying to take it up. For example:
“That the
kidneys of marine fish have powerful renal mechanisms for the
excretion of magnesium (Mg) from the body has been known since
the early 1930s…”11
Toxicity
of Elevated Magnesium
There have been
very few studies on the toxicity of elevated magnesium on most
marine organisms. Most
toxicity studies involving magnesium use freshwater species.
This is largely true because magnesium is already quite high
in concentration in normal seawater, so to significantly elevate
it requires conditions that would rarely be encountered in oceans
or even lagoons.
Bingman12
pointed out in a previous article that at elevated concentrations
(>8,000 ppm), magnesium has been used as an aid in shucking
oysters, helping to force the oyster open,12-14 and
also as an anesthetic for them.12 Consequently, magnesium
does have potentially negative biological effects at significantly
elevated concentrations.
Toxicity
of Depleted Magnesium
Like elevated magnesium, there are not very many studies on
the effects of depleted magnesium on creatures likely to be
present in aquaria. Except in estuaries and at the outflow of
hydrothermal vents, magnesium is not likely to be depleted in
marine systems. Consequently, few scientists have much interest
in studying such depletion. It is known that many marine bacteria
do require magnesium, but in some cases, just a little magnesium
is adequate.8-10 On first principles, all autotrophs
(organisms that get all of their energy from photosynthesis,
including all algae) must get their required magnesium from
the water column. How high the magnesium concentration needs
to before they become limited by magnesium, however, is not
known.
Magnesium
in Marine Aquaria
Magnesium has tremendous biological and chemical relevance to
reef aquaria. Fortunately for reefkeepers, it is present in
abundance in seawater. There is, in fact, a fairly high turnover
of magnesium in reef aquaria with rapidly calcifying organisms.
The primary reason that magnesium is not more of a daily concern
to aquarists is that the reservoir of magnesium in seawater
is very large. Magnesium might be compared to a large lake,
with the lake level only slowly responding to changes in inputs
from rivers and export via evaporation and the outlet. Consequently,
maintenance of magnesium levels is not typically a rapidly developing
problem. If using an appropriate salt mix, it may never become
a problem for many aquarists. Nevertheless, over the long run
the levels can change significantly if the inputs and exports
do not roughly match. The following sections will describe these
inputs and exports, and will also describe what happens if the
magnesium gets too low.
Sources
of Magnesium in Marine Aquaria
The obvious primary
source of magnesium in aquaria is the artificial or natural
seawater used to set up the aquarium, and with which any water
changes are performed. Some artificial salt mixes have been
reported to be deficient
in magnesium.15 These include Tropic Marin and
Seachem. Others have been reported to have a substantial
excess, including Coralife.15
The other major
source is calcium supplements. Many of these supplements contain
magnesium, either by “accident” (as in the case
of calcium carbonate with impurities of magnesium carbonate
that is used in CaCO3/CO2 reactors) or
because magnesium is intentionally added by manufacturers.
In the case of commercial
calcium supplements, some manufacturers add magnesium to some
of them. Seachem, for example, adds magnesium to Reef Complete
and Reef Advantage Calcium, but not to their other calcium products.
When formed into the equivalent of a calcium carbonate skeleton,
the amount added is equivalent to about 2% by weight magnesium
in the “skeleton”. As will be seen below by comparison
to other methods, that is fairly high. How much is an optimal
amount to add, however, is not entirely clear, and this “problem”
of matching the input of magnesium to the export is discussed
in detail below. Other manufacturers, such as Kent, do not add
magnesium to any of their normal calcium supplements. Nevertheless,
these supplements will all contain some magnesium. The question
is how much.
In some cases,
most notably that of limewater (kalkwasser), it is not clear
that all of the magnesium present in it actually makes it into
aquaria. Magnesium hydroxide may settle from solution prior
to addition to the aquarium. Consequently, even though analyses
of commercial lime products show fairly large amounts of magnesium
(the quicklime
that I use would produce a calcium carbonate skeleton with
approximately 1.8% magnesium by weight),16 how much
makes it into aquaria is likely a complicated function of how
much lime is added to how much water, how long it is allowed
to settle (if at all), and whether any vinegar is added into
the milieu. These issues will be explored experimentally in
a future article.
Even when the included
magnesium is nearly all getting into the aquarium, as in a CaCO3/CO2
reactor, striking a perfect balance between input and export
may require occasional measurements and adjustments. The argument
that using ground up coral skeletons in a CaCO3/CO2 reactor
will supply exactly what corals need is too simplistic. Different
sources of calcium carbonate have different amounts of magnesium
in them. In testing of samples used by aquarists, Bingman18
reported 0.1% by weight magnesium for Korlith and 0.28% magnesium
for Super Calc Gold. Similarly, Hiller18
reported 0.4% by weight magnesium for a quarried limestone and
0.26% magnesium for Nature's Ocean brand crushed coral.
Further complicating
the lives of aquarists is the fact that different organisms
use different amounts of magnesium relative to calcium (Table
1, where the organisms are seen to range from 0.05% to 4.4%
magnesium by weight in the skeleton). Consequently, the optimal
amount of magnesium to provide to an aquarium, relative to calcium
input, is going to depend on exactly what organisms are in the
aquarium. For this reason, one may find that simple use of any
particular calcium and alkalinity supplementation scheme may
lead to magnesium declining (or rising) over time. These issues
will be addressed more extensively in future articles.
Another potential
source of magnesium is fish food. Magnesium is present in many
such foods at fairly high concentrations, but not enough to
have a significant impact on typical levels of magnesium (~1285
ppm). Table 2 shows some data from Shimek19
that have been recalculated to show the effect of adding 5 grams
of food per day to a 100-gallon aquarium for a year. The effect
on magnesium of 1-14 ppm assumes that all of the magnesium goes
into solution. Whether that actually happens or not is moot
as the total contribution to magnesium is small. Also shown
in Table 2 are the same data for calcium, showing that some
foods could add a significant amount of calcium to reef aquaria.
Table
2: Calcium and Magnesium in Aquarium Foods
Food
Calcium
Concentration (ppm)
Calcium
added to 100 gallon tank in 1 year (ppm in aquarium)
Magnesium
Concentration (ppm)
Magnesium
added to 100 gallon tank in 1 year (ppm in aquarium)
Formula One
800
4
280
1
Formula Two
1700
8
290
1
Prime Reef
860
4
290
1
Lancefish
4700
23
520
3
Silversides
4300
21
560
3
Brine Shrimp
140
1
300
1
Plankton
1700
8
520
3
Golden Pearls
8700
42
920
4
Gold Flakes
7200
35
1300
6
Tahitian Blend
440
2
290
1
Saltwater Staple
17000
82
1800
9
Nori
2400
12
2900
14
Sinks for
Magnesium in Marine Aquaria
The primary sink
for magnesium in aquaria is coprecipitation with calcium carbonate.
This occurs in organisms, as shown in Table 1, and also during
the abiotic (non-biologically driven) precipitation of calcium
carbonate (such as on heaters).
A potential sink
that has been described by some hobbyists is the precipitation
of magnesium by limewater (kalkwasser). Both magnesium hydroxide
and magnesium carbonate have been suggested. I do not believe
that either is an important process in most aquaria. Adding
any high pH additive, including limewater, results in the transient
formation of magnesium hydroxide. This material quickly redissolves
on mixing such that the local pH drops below about 8.6.-9.0.
Magnesium carbonate is a more complicated issue, as it is near
its solubility limit in seawater and may quickly get coated
with a less soluble magnesium calcite. These issues have been
dealt with by Bingman20
in much greater detail, and his conclusion is that neither of
these precipitates is a likely sink for magnesium.
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I would suggest
that an alternative way that aquaria using only limewater might
become deficient in magnesium over time is that the limewater
is simply not delivering magnesium to the aquarium even though
it is present in the solid lime. How and why this might happen
was discussed above involving the precipitation of magnesium
hydroxide in the limewater reservoir. This lack of addition
coupled to the ongoing removal of magnesium in calcification
could lead to deficiencies in magnesium. Such deficiencies have
not become extensive in my aquarium, but it does not have an
especially high rate of calcification, and perhaps water changes
have eliminated the problem. In any case, those using only limewater
(or other systems that do not deliver magnesium) may want to
occasionally check magnesium.
Supplements
for Magnesium in Marine Aquaria
There are a variety
of commercial supplements for magnesium. Those supplements made
by ESV, Seachem, and Kent are quite popular, although I’ve
not seen any detailed analyses of them. Assuming they are what
they claim to be, they are fine products to use, even for large
increases in magnesium. I’ve used the ESV supplement,
along with ones that I’ve made myself.
One thing to keep
in mind about magnesium supplements is that they are all necessarily
quite “dilute” even when presented as dry solids.
The reason for this is that magnesium is a doubly charged and
very light ion. So in a salt form, or when dissolved in a liquid,
it is necessarily attended by a large number of quite heavy
counterions (chloride and sulfate, especially). Commercial dry
supplements may be only 8% magnesium by weight, for example.
Compounding the
issue is the simple fact that there is so much magnesium in
an aquarium that significant supplementation requires a great
deal of material. A 100-gallon aquarium contains about a pound
of magnesium! In order to raise that same aquarium by 200 ppm
of magnesium, one would need to add on the order of 2 pounds
of dry magnesium salts!
Epsom Salts (USP
grade magnesium sulfate heptahydrate) is readily available in
drug stores and very inexpensive. The problem is that if you
were to raise magnesium by a large amount (or a small amount
several times) the aquarium water will become relatively enriched
in sulfate. This enrichment may not be a problem for some aquaria,
especially those using salt
mixes already deficient in sulfate,15 or those
that experience frequent water changes. Bingman21
has addressed these enrichment issues and has suggested a recipe
for home made supplements based on Epsom Salts and magnesium
chloride. The problem is in getting the latter in adequate purity.
As an alternative,
some aquarists have begun to use Nigari,
a Japanese product that is derived from seawater and is used
to manufacture tofu. It appears to be mostly magnesium salts
of chloride and sulfate, but how much sulfate and how much chloride,
as well as what other metals remains to be demonstrated.
Whatever
supplement you choose, I’d suggest targeting the natural
seawater concentration: 1285 ppm. For practical purposes, 1250-1350
ppm is fine. I would not suggest raising magnesium by more than
100 ppm per day. If you need to raise it by several hundred
ppm, splitting the addition over several days will allow you
to better home in on the target concentration, and might possibly
allow the aquarium to deal with impurities that may come in
with the supplement.
It has been suggested
that adding dolomite to CaCO3/CO2 reactors
can help with magnesium problems. Dolomite is a material that
contains both magnesium and calcium carbonate. If dolomite is
being added to the reactor to maintain existing appropriate
magnesium levels against the continual depletion via calcification
(for example, if the calcium carbonate being used is too low
in magnesium to maintain adequate magnesium) then this is a
fine approach.
However,
this method is unsuitable if the goal is to raise magnesium
levels. The problem is that for every magnesium ion
released from the dolomite, 2 units of alkalinity are also released:
MgCO3
Mg++ + CO3--
Consequently, if
one wants to raise magnesium by 100 ppm, the alkalinity will
necessarily rise by 8.2 meq/L (23 dKH). The only way around
this problem is to add a mineral acid (not vinegar) to the aquarium
to reduce the alkalinity, and that may be more problematic than
just adding magnesium in the first place.
Measuring
Magnesium in Marine Aquaria
There are a number
of commercial magnesium test kits available, including those
made by Hach, Salifert, and Seachem. These kits have various
ways of trying to distinguish magnesium from calcium. Some,
like the Hach kit, require 2 titrations, but you end up with
magnesium and calcium readings. Others, like the Seachem kit,
require only a single titration, but yield only a magnesium
value when used that way. In most cases, simply following the
manufacturer directions will get you what you want, but the
units are sometimes complicated. The Hach kit, for example,
reports magnesium in units of calcium carbonate equivalents!
While this facilitates the subtraction process used in the Hach
kit to arrive at a magnesium value, it also serves to confound
many aquarists. Hopefully future versions of that kit will strive
to make the units more clear. For those interested, Bingman22
has a more detailed discussion of the chemistry involved in
these kits.
Effect
of Magnesium on the Calcium/Alkalinity Balance in Aquaria
How does magnesium
impact the balance
of calcium and alkalinity23 in reef aquaria?
In order to answer that question, one has to have a basic understanding
of the calcium and carbonate systems in seawater. These systems
have been discussed in detail in a variety of previous articles,
so I won't go into them here in great detail. In short, calcium
carbonate (CaCO3) is supersaturated
in seawater,24 meaning that given enough time
calcium ions will interact with carbonate ions and precipitate
as calcium carbonate. If you push the concentration of either
too high, CaCO3 will start to precipitate. Magnesium interferes
with this process, permitting both calcium and carbonate to
be elevated above where they would be in the absence of magnesium.
If this sounds
confusing, don’t feel alone. In Stephen Spotte's book
Captive Seawater Fishes, Spotte says “The
study of carbonate minerals involves nuances of solubility that
pose some of the most difficult problems in chemical oceanography
and geochemistry.”25 Nevertheless, the following
section will attempt to give a simplified version that suits
our level of understanding as aquarists.
How does magnesium
interfere with precipitation of CaCO3? The primary
way involves magnesium poisoning the surface of growing CaCO3
crystals, slowing the precipitation. It can, in fact, be slowed
to the point where it simply does not happen at rates problematic
to an aquarist. In the following discussion it is important
to remember that, other things being equal, alkalinity is a
good indicator of the concentration of carbonate. So higher
alkalinity equates to higher carbonate.
In short, while
magnesium carbonate is not supersaturated in seawater (or in
typical reef aquaria), and will not precipitate on its own,
magnesium is attracted to calcium carbonate surfaces where the
carbonate ions are already held in place by the calcium ions.
With the carbonate ions held in place, magnesium finds this
an attractive place to bind.
After a short time
in seawater, a virgin calcium carbonate surface quickly attains
a thin coating of Mg/CaCO3 (magnesian calcite) as
magnesium pushes its way into and onto the crystal surface.
Eventually, the surface contains a substantial amount of magnesium.
The extent to which this happens depends on the underlying mineral,
and is apparently much more extensive on calcite than aragonite.
It also depends upon the relative amounts of calcium and magnesium
in the water. Regardless, a new type of material is formed that
contains both calcium and magnesium.
This new mineral
surface containing both calcium and magnesium is not a good
nucleating site for precipitation of additional calcium carbonate
(as aragonite or calcite), and precipitation of additional CaCO3
slows down substantially.
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In Captive
Seawater Fishes there is an extensive discussion of
the impact of magnesium on the calcium/carbonate system, including
a set of data that indicates the magnitude of the impact that
magnesium can have.25 In this experiment, batches
of artificial seawater were made up with varying magnesium and
carbonate levels. The scientists then measured how long it took
for calcium carbonate to precipitate from each solution. Not
surprisingly, the higher the carbonate was raised, the more
rapid was the precipitation of calcium carbonate.
More interestingly,
the magnesium levels were found to have a very large impact
on the rate of precipitation. In batches with no magnesium,
and at natural calcium and elevated carbonate levels, calcium
carbonate was found to precipitate in minutes. With a natural
seawater level of magnesium added to that mix, the precipitation
was delayed to 13 to 20 hours. With double the natural magnesium
concentration, the precipitation was delayed to 22 to 29 hours.
Even more strikingly,
at a lower level of carbonate (closer to that of natural seawater
and probably similar to that in many reef aquaria), precipitation
was delayed from a few minutes in the absence of magnesium to
750 hours in the presence of natural levels of magnesium. Consequently,
magnesium has a big impact on the rate of precipitation of calcium
carbonate (a fact that has been confirmed by many researchers).
But what does that
have to do with a reef aquarium? One situation in which calcium
carbonate can precipitate involves adding calcium carbonate
seed crystals of some type to the aquarium. For example, by
adding calcium carbonate sand or one of the calcium
carbonate supplements like Aragamight or Kent’s Liquid
Reactor.26
A second situation
where solid CaCO3 forms is when abiotic
precipitation initiates in the aquarium.24 This
precipitation happens when supersaturation is pushed to unusually
high levels (either in the tank as a whole, or in localized
regions). This rise in supersaturation can be caused by a rise
in pH (which increases the amount of carbonate present by converting
bicarbonate into carbonate), a rise in temperature (as on a
heater or pump impeller; the temperature rise decreases the
solubility of calcium carbonate and also converts bicarbonate
into carbonate), or more directly by a rise in either calcium
or carbonate.24
After the solid
calcium carbonate has appeared in the system by whatever means,
precipitation of CaCO3 will begin immediately. What
processes inhibit continued precipitation of CaCO3
onto a growing crystal? The main thing happening in normal seawater
is likely the impact of magnesium (though phosphate and organics
may play an important role in some aquaria).24 This
is the point that magnesium gets onto the growing surface of
the crystal, essentially poisoning it for further precipitation
of calcium carbonate. Since magnesium can reduce the likelihood
or extent of calcium carbonate precipitation in this fashion,
it thus acts to make it easier to maintain high levels of calcium
and alkalinity.
Conclusions
Magnesium is an
important ion for reef aquarists. In addition to its many biological
functions, it serves to prevent the excessive precipitation
of calcium carbonate from both seawater and aquarium water.
Since both calcium and alkalinity are very important to organisms
that we keep, making sure that they are not lost to excessive
precipitation is an important part of aquarium husbandry.
Happy Reefing!
References
1. Low-magnesium
calcite produced by coralline algae in seawater of Late Cretaceous
composition. Stanley, Steven M.; Ries, Justin B.; Hardie,
Lawrence A. Morton K. Blaustein Department of Earth and Planetary
Sciences, The Johns Hopkins University, Baltimore, MD, USA.
Proceedings of the National Academy of Sciences of the United
States of America (2002), 99(24), 15323-15326.
2. New data
on the relation between the magnesium content of reef-forming
corals and their systematic location and stages of growth.
Pozdnyakova, L. A.; Krasnov, E. V. Inst. Biol. Morya, Vladivostok,
USSR. Doklady Akademii Nauk SSSR (1981), 260(3), 739-40 [Paleontol.].
3. Magnesium
content of calcite in carapaces of benthic marine Ostracoda.
Cadot, H. Meade, Jr.; Kaesler, Roger L. Harris Cent. Conserv.
Educ., Hancock, NH, USA. University of Kansas Paleontological
Contributions, Papers (1977), 87 23 pp.
4. Assessment
of calcareous alga Corallina pilulifera as elemental provider.
Yan, Xiaojun. Institute of Oceanology, Chinese Academy of Sciences,
Tsingtao, Peop. Rep. China. Biomass and Bioenergy (1999), 16(5),
357-360.
5. Calcium
and magnesium carbonate concentrations in different growth regions
of gorgonians. Velimirov, B.; Boehm, E. L. Dep. Zool.,
Univ. Cape Town, Rondebosch, S. Afr. Marine Biology (Berlin,
Germany) (1976), 35(3), 269-75.
6. Biochemistry
of the coral. IX. Inorganic composition of the skeleton of the
coral. Hosoi, Keizo. Sendai, Japan. Science Repts.
Tohoku Univ. (1947), 18 85-7.
7. Oxygen
and carbon isotopic composition of carbonates deposited by red
algae in the middle Adriatic. Dolenec, Tadej; Herlec,
Uros; Pezdic, Joze. Fakulteta za Naravoslovje in Tehnologijo,
Univerza v Ljubljani, Ljubljana, Slovenia. Rudarsko-Metalurski
Zbornik (1995), Volume Date 1994, 41(3-4), 193-202.
8. The marine
bacteria. II. The specificity of mineral requirements of marine
bacteria. Hidaka, Tomio. Univ. Kagoshima, Japan. Kagoshima
Daigaku Suisangakubu Kiyo (1965), 14 127-80.
9. Nutrition
and metabolism of marine bacteria. II. The relation of sea water
to the growth of marine bacteria. MacLeod, Robert A.;
Onofrey, E. Pacific Fisheries Exptl. Sta., Vancouver, BC, Can.
Journal of Bacteriology (1956), 71 661-7.
10. Nutrition
and metabolism of marine bacteria. I. Survey of nutritional
requirements. MacLeod, Robert A.; Onofrey, Eva; Norris,
Margaret E. Pacific Fisheries Expt. Sta., Vancouver, BC, Journal
of Bacteriology (1954), 68 680-6.
11. Epithelial
transport of magnesium in the kidney of fish. Beyenbach
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14. Chemical
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Mg++ + CO3--