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143
Chapter 15
Trace elements, functions, sinks and replenishment
in reef aquaria
Ha n s -We r n e r Ba l l i n g 1, Ma x Ja n s e 2 a n d Pi e t J. so n d e r v a n 3
1Hauptstraße 54, 36341 Lauterbach, Germany
hans-werner.balling@tropic-marin.com
2Burgers’ Zoo, Antoon van Hooffplein 1, 6816 SH Arnhem, The Netherlands
3Aqua Bio Solutions, Zuideinde 310, 1035 PN, Amsterdam, The Netherlands
ABSTRACT
Trace elements in closed or semiclosed marine aquaria are a matter of permanent
discussion.
As the name states the concentrations of trace elements are extremely low and quantitative
analyses are difcult. They play important roles as parts of enzymes in metabolism and
enrichment in organisms is achieved often under high expenditures. For corals, trace
elements besides physiological roles also have an important role in the skeleton. Also
zooxanthellae are in need of many trace elements. Due to consumption and precipitation
within aquarium systems addition of trace elements is necessary. This can be done via
food, water changes or chemical addition. With published data about the concentrations
and distributions of trace elements in the ocean, additions can be calculated.
This paper will describe the biological and physiological functions of the different trace
elements. A recipe for the supplementation of essential trace elements calculated
from the most important sinks in reef aquaria will be given. A summary of addition
experiences in public aquaria and institutions will be presented and discussed.
Bioavailability of trace elements as well as bioindication of trace element intoxication
is discussed. At last some recommendations for rst aid measures at suspected trace
element intoxications are given.
Advances in Coral Husbandry in Public Aquariums. Public Aquarium Husbandry Series, vol. 2. R.J. Leewis and M. Janse (eds.), pp. 143-156
© 2008 Burgers’ Zoo, Arnhem, the Netherlands.
INTRODUCTION
Elements that are present in a medium in very low
concentrations, in concentrations of mg.kg-1 (ppm)
or lower, are generally named trace elements.
This article will take a closer look only on those
elements that have a function in metabolism or
calcication of marine organisms. Trace metals
in this interpretation are strontium, barium,
vanadium, chrome, molybdenum, manganese,
iron, cobalt, nickel, copper, zinc, cadmium,
boron, silicon, selenium, uorine, bromine and
iodine. Table 1 gives a short overview over the
functions of these trace elements.
TRACE ELEMENTS IN CORALS
Trace elements in corals – functions,
bioinorganic chemistry
Some of the most important functions of trace
elements, in particular of transition metals,
are related to the regulation of metabolism by
enzyms. Enzyms are proteins that speed up
chemical reactions in biological processes or
make them possible at all under physiological
conditions. Typical mechanisms are multi-
electron transformations as photosynthesis,
respiration and nitrogen xation. These enzyms
contain transition metals that can exist in
multiple oxidation states like for example iron.
In hydrolytic transformations like proteolysis
and the equilibration of carbonic dioxide and
bicarbonate ion transition metals do not change
oxidation state but function as Lewis acid-type
catalysts. An example for a hydrolytic enzyme
is the carbonic anhydrase shown in Figure 1.
This enzyme contains zinc as a cofactor, a non-
protein component that activates the enzyme.
The biochemical reaction catalysed by carbonic
144
anhydrase is the hydrolysis of carbonic dioxide
as shown in Figure 2. This hydrolytic reaction is
speeded up by a factor of 107 by the enzyme.
Sometimes the same or very similar processes
are catalysed by different enzymes, so called
isoenzymes, under different conditions.
Obviously the symbiosis of anemones and
corals with zooxanthellae makes diverse
superoxide dismutases (SODs) necessary
to survive the change from hypoxia (oxygen
deciency) to hyperoxia (over-supply of
oxygen) within minutes without damage
(Richier et al., 2003). These SODs work with
Figure 1: Human carbonic anhydrase. The zinc cofactor is shown as a grey sphere in the middle (De Boer et al., 2006).
Figure 2: Hydrolysis of CO2 by Carbonic Anhydrase (www1)
different transition metals. In the symbiotic
Mediterranean anemone Anemonia viridis and
its zooxanthellae, SODs with copper and zinc
(CuZnSOD) in ectoderm and endoderm, with
manganese (MnSOD) in all compartments
and with iron (FeSOD) in zooxanthellae and
endoderm have been found. This means in
this anemone four different transition metals
are involved in the detoxication of reactive
oxygen species. These are just few examples
on how different trace elements play central
roles in the metabolism of all organisms
including corals.
H3O+ + HCO3
- + His64 His64
2H2O + His64H His64H
Zn2+ OH
H
Zn+ OH
N
N
N
N
N
N
Zn+ O
H
N
N
N
Zn+O
O
COH
O
O
CCO2
His94
His96
His119
His94
His96
His119
His94
His96
His119
His94
His96
His119
N
N
N
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
145
CH a P t e r 15: tr a C e e l e M e n t s , f u n C t i o n s , s i n k s a n d r e P l e n i s H M e n t in r e e f a q u a r i a
Table 1: Functions of trace elements
Element General function Enzymes (examples) citations
Strontium
Barium
Vanadium
Chrome
Molybdenum
Manganese
Iron
Cobalt
Nickel
Copper
Zink
Gets incorporated into the aragonite
skeletons of scleractinian corals,
stabilizes the aragonite modication of
calcium carbonate and supports skeletal
growth. No further biological functions
known.
Similar to strontium but less abundant.
High concentrations in ascidians.
Production of bromoform in algae to
repel epiphyts. Alternative nitrogenase
for nitrogen-xation.
Glucose-tolerance-factor for the proper
function of insulin.
Electron transfer
Electron transport, hydrogen transfer,
protein metabolism, citrate cycle, RNA
and DNA synthesis, detoxication of
reactive oxygen species.
Redox systems, electron transport
chain, oxygen transport, detoxication of
reactive oxygen species.
Vitamin B12, redox reactions,
methylations, nutrient for algae.
Hydrolysis of urea, bacterial methane
and acetate production.
Oxygen transport, respiration chain,
electron transfer, oxidations (preferably),
reductions, competing and displacing
against iron and manganese.
Hydrolysis of bicarbonate, hydrolysis
of proteins in digestion, hydrolysis of
phosphate esters, energy metabolism,
carbohydrate metabolism, oxidation
of alcohols, detoxication of reactive
oxygen species.
-
-
Bromoperoxidase of
algae, nitrogenase
-
Nitrogenase, nitrate
reductase, sult
reductase
Oxygen evolving
complex of
photosystem II,
superoxide dismutase,
phosphatases.
FeS of photosystem I,
cytochrome oxidase,
katalase, peroxidase,
superoxide dismutase.
Coenzyme B12 of many
enzymes like mutases.
Urease, CO
dehydrogenase.
Hemocyanin,
plastocyanin, ascorbate
oxidase, tyrosinase,
cytochrome c oxidase,
Cu-Zn superoxide
dismutase, nitrite
reductase, N2O
reductase.
Carbonic anhydrase,
carboxypeptidase,
alkalinic phosphatase,
alcohol dehydrogenase,
Cu-Zn superoxide
dismutase
1
1
2
2
3
4
4
2
2
4
4
Cadmium
Boron
Selenium
Biological function only in alternative
carbonic anhydrase of diatom
Thalassiosira weissogi, only toxic for
other organisms.
Stabilization of cell membrane, multiple
functions and regulations in metabolism
but mechanisms are not well understood.
Antioxidans, quenching of radicals.
Carbonic anhydrase
-
Peroxidase
5
6
2
146
Table 1 (continued): Functions of trace elements
Fluorine
Bromine
Iodine
Hardening of biominerals, heavy metal
complexation.
Bromoform is produced by algae as
repelling agent against epiphytes.
Similar to bromine, constituent of
hormones, hardening of exoskeletons of
sponges, crustaceans and gorgonians,
highly enriched in algae, especially in
brown algae. Iodate (IO3
-), which is the
stable form under surface conditions, is
reduced to iodide by nitrate reductase
in algae, protecting the photosynthetic
apparatus under high irradiation in this way.
-
-
-
2
2
7
Element General function Enzymes (examples) citations
1 Milliman, (1974), Balling (1995, 1996)
2 Kaim and Schwederski (1995)
3 Mengel (1991)
4 Kaim and Schwederski (1995), Amberger (1996)
5 Lane (2005)
6 Mengel (1991), Amberger (1996)
7 Kaim and Schwederski (1995), Balling (1995, 1996)
A C
D
B
His44
His118
His46
Cu Zn
His61
His69
His78
Asp81
Zn
Cu
Ala165
Ala238
Asp155
Lys14
Thr62
Val95
a1
b1
a2
a5
a4
a6
a7
a3
b2
b3
Figure 3: Dimer of CuZnSOD (A) with detail of active site (B, both www2), monomer of FeSOD (C, www3) and of
MnSOD (D, www4).
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
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Trace elements in corals – concentrations
Table 2 shows the trace metal concentrations
of the components of the scleractinian coral
Acropora tenuis. The skeleton reects the
concentrations of trace elements in the
surrounding water (Druffe, 1997; Mokhtar et
al., 2002; Fichez et al., 2005; Madkour, 2005;
Al Ouran, 2005). Further data on the trace
element concentrations of coral skeletons are
given in table 3. An extensive overview with
data on the heavy metal concentrations of hard
coral skeletons is also given in Reichelt-Brushet
and Orist (2003). Skeletons show the least
enrichment of trace elements of all parts, which
will be important for our later calculations.
A closer study of the concentrations shows
that coral tissue shows the smallest variability
in trace metal concentration. This conrms the
nding (Fisher, 2002) that essential trace metals
are more or less under homeostatic control.
Surprisingly the trace metals in the zooxanthellae
are highly variable and of high concentration.
This may be the cause why the zooxanthellae
show signs of stress while the polyp of the
Table 2: Trace element concentrations found in Acropora tenuis zooxanthellae, tissue and skeleton (µg.g-1) from
Magnetic Island and One Tree Island.(Reichelt-Brushett and Orist (2003), altered, except * from Millero (1996))
Acropora tenuis
Magnetic Island
Zooxanthellae
a
b
Tissue
a
b
Skeleton
a
b
One Tree Island
Zooxanthellae
a
b
Tissue
a
b
Skeleton
a
b
Seawater,
average*
Br a
µg.g-1
33 ± 7
25 ± 9
105 ± 9
227 ± 24
1.3 ± 0.4
1.1 ± 0.3
75 ± 22
36 ± 3
161 ± 14
7 ± 3
< 1
1 ± 0.3
67.1
I a
µg.g-1
4 ± 3
6 ± 4
< 5
< 9
6 ± 4
8 ± 5
12 ± 8
6 ± 4
< 10
<1
6 ± 3
7 ± 3
58.4
* 10-3
Ba a
µg.g-1
45 ± 20
89 ± 17
690 ± 70
930 ± 150
116 ± 23
55 ± 16
470 ± 50
105 ± 40
660 ± 80
-
80 ± 17
64 ± 21
13.7
* 10-3
Fe b
µg.g-1
379.8
292.4
23.3
32.4
16.3
ND
301.3
298.2
22.2
7.2
ND
ND
0.055
* 10-3
Mn b
µg.g-1
3.52
1.99
1.38
1.67
0.15
0.09
1.86
1.57
1.55
0.11
0.02
0.01
0.027
* 10-3
Ni b
µg.g-1
14.4
7.5
1.8
3.8
1.1
0.7
5.4
11.5
2.3
0.7
0.6
0.3
0.47
* 10-3
Cu b
µg.g-1
15.7
11.5
1.0
1.1
0.06
0.10
0.73
0.62
1.2
0.4
0.03
0.08
0.25
* 10-3
Zn b
µg.g-1
128.1
42.6
19.5
17.1
1.8
0.5
25.1
32.3
18.6
17.3
0.3
0.2
0.39
* 10-3
a NAA
b ICPMS
coral remains nearly unaffected by moderately
elevated trace metal concentrations.
Trace elements in corals – stress and
intoxication
While an elevated concentration of iron increases
number of zooxanthellae in corals but decreases
growth rate (Ferrier-Pages et al., 2001),
enrichment with copper decreases zooxanthellae
density and can partially bleach corals (Jones,
1997). No signicant change was detected in any
other function after exposure to copper between
0.01 and 1.0 mg.L-1 (Howard et al., 1986).
The mechanism of bleaching is competition
of heavy metal ions with iron for uptake (De
Haan, 1984; Pätsikkä et al., 2002; Hirose,
2006), inhibition of photosystem II by copper
outcompeting iron (Burda et al., 2002) and by
induction of oxidative stress by various heavy
metals (Pinto et al., 2003)
Experiments with symbiotic (containing
zooxanthellae) and aposymbiotic (without
zooxanthellae) specimens of Anthopleura
elegantissima conducted by Mitchelmore et al.,
148
Table 3: Trace element concentrations of scleractinian coral skeletons
Acropora
sp.1
Acropora
humilis2
Acropora
hemprichii2
Acropora
hyazinthus2
Madracis
sp.1
Meandrina
sp.1
Meandrina
areolata3
Meandrina
braziliensis3
Meandrina
braziliensis3
Madracis cf.
pharensis3
Madracis
mirabilis3
Montastrea
sp.1
Montastrea
annularis3
Phyllangia
americana3
Pocillopora
damicornis2
Porites
sp.1
Porites
compressa2
Porites
lutea2
Porites
porites3
Scolymia
ubensis3
Scolymia
cubensis3
Stylophora
wellesi2
38.8
39.1
38.1
38.5
37.6
38.1
38.1
40.0
39.0
39.6
38.1
39.4
36.8
38.6
36.0
0.81
0.85
0.85
0.83
0.87
0.85
0.83
0.86
0.68
0.80
0.77
0.79
0.71
0.75
0.75
24
42
32
85
10
38
11
17
10
27
15
15
9
43
65
49
72.6
250.7
35
13
30
< 5
8
10
< 5
12
5
290
51.0
80
62.4
179.2
45
13
880
33.6
6
2.5
2.9
7.0
4
2
< 5
< 2
< 2
4
< 2
3
< 2
130
7.6
6
13.1
3.7
4
3
30
2.5
4.4
0.4
0.5
2
2
< 2
< 2
< 2
2
2
3
2
0.6
0.4
0.6
< 2
3
3
2.0
1
3.7
0.7
0.8
3
5
1
8
5
< 2
6
2
20
2.4
4
4.2
3.1
2
< 2
16
0.6
8.5
7.3
15.8
< 2
< 2
2
2
2
2
< 2
< 2
7
2.0
< 2
3.5
7.5
< 2
< 2
3
6.5
13
< 1
< 1
1.1
< 2
23
5
10
< 2
< 2
2
5
0.5
0.7
0.5
0.1
0.05
0.04
0.058
0.067
0.077
0.1
0.064
< 2
0.4
0.3
0.2
2
0.058
0.47
0.5
21
85
78
110
70
55
80
80
57
50
60
21
15
80
60
Species Ca
%
Sr
%
Ba
µg.g-1
Fe
µg.g-1
Mn
µg.g-1
Ni
µg.g-1
Cu
µg.g-1
Zn
µg.g-1
Cr
µg.g-1
Co
µg.g-1
B
µg.g-1
1 Milliman (1974);
2 Madkour (2005);
3 Livingston and Thompson (1971)
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
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CH a P t e r 15: tr a C e e l e M e n t s , f u n C t i o n s , s i n k s a n d r e P l e n i s H M e n t in r e e f a q u a r i a
(2003) showed that the expulsion of zooxanthellae
may be a detoxication mechanism for copper.
Obviously elevated copper concentrations are
taken up by the zooxanthellae and get disposed
when zooxanthellae are released, moderating
copper accumulation in this way. Symbiotic
anemones accumulated more cadmium, zinc
and nickel than aposymbiotic ones. Symbiotic
anemones returned to pre-exposure levels after
nickel exposure.
Exposed to copper, symbiotic A. elegantissima
also produced more mucus than aposymbiotic
ones, wrapping them in a thick layer of mucus.
Algal cell density in A. elegantissima was
reduced by nickel and high zinc levels.
Similar results where achieved with Anemonia
viridis in similar experiments by Harland and
Nganro (1989).
Multi-element analysis in seawater
Analyzing trace and minor elements in seawater is
complicated, the disturbance of high halogenide
concentrations against the sometimes very
low element concentrations is immense. Most
regular analytical laboratory procedures are
not suitable. Inductive coupled plasma optical
emissions spectroscopy (ICP-OES) formerly
called inductive coupled plasma atomic emission
spectroscopy (ICP-AES) and inductive coupled
plasma-mass spectrometry (ICP-MS) are the
most useful methods for determination even
very low quantities of elements.
These spectroscopic techniques exploiting
the fact that under certain circumstances
excited electrons of elements emit energy at a
specic wavelength peculiar to their chemical
character. This happens in a gaseous state (the
plasma). The intensity of the energy emitted is
proportional to the amount (concentration) of
the analyzed element. By determining which
wavelengths are emitted and determining the
intensities, the elemental composition of a
sample can be quantied relative to a reference
standard. ICP-OES is useful to determine Na, K,
Ca, Mg, B, Sr, S and P, while ICP-MS is suitable
for determination Sb, Co, Mn, Zn, Cu, As, Se,
Al, Ti, Fe, Cr, Si, Mo, Li, Ti, Co, Ni, Br and Ba.
Some major elements such as calcium and
magnesium can easily be measured by
titrimetry, spectroscopical analitycal methods
(Anonymous, 1999, 2000), or commercial
available suitable testkits.
Not all elements can be analyzed by the ICP-
OES and ICP-MS methods, because of its
complexity behaviour. Iodide (Luther and Cole,
1988) and iodate (Herring and Liss, 1974) can
best be measured by a polarographic method,
the voltametric method in which the current is
measured as a function of applied potential,
using a dropping mercury electrode.
The specic method for iodide is called cathodic
stripping square wave voltammetry (CSSWV) and
for iodate differential pulse polarography (DPP).
Measuring trace elements can best be carried
out by specialized laboratories.
The most convenient way of reaching the best
environment circumstances for coral husbandry
is to measure besides calcium, magnesium and
strontium the following elements at a regular
basis K, Fe, Si, Mo, Mn, I, Li, Al, Ti, Cr, Co, Ni,
Cu, Zn, Br, Ba.
Comparing such results with references of
natural seawater prevents surprises, table 4
gives just an example.
Analyzing trace elements in institutions
To obtain a view what kind of analyzing efforts
public aquariums perform and which element
additions are being used, a questionnaire
was send out on the aquaticinfo list server, 15
institutions responded.
Natural seawater was used in 53% of the
institutions the rest used articial seawater.
Many aquariums (53%) measure trace elements
on weekly, monthly or yearly basis, with
spectrophotometry, ICP-MS and ICP-OES.
67% of the institutions are adding some kind of
trace element mixtures into their systems, half
of them used commercial available solutions,
others had mixtures composed by their own.
Control of the effects of these additions was
performed in 90% by bio monitoring and in
some cases completed with measurements.
Positive effects were mentioned but also doubts
if these effects were related to the additions
only. As references Spotte (1992), Delbeek and
Sprung (1994) and Nilsen and Fossa (2002)
were mentioned.
The importance of analyzing water quality is
understood, but only 50 % of the institutions is
measuring in some way. However the number
of answered questionnaires was limited.
From the institutions that are adding
mixtures into their systems little is known
what really happens. Measuring shortness
or overdimensioned additions of elements
(Sondervan, 2001) is not carried out on a
regular basis. This seems to be a small basis
for proper husbandry when handling is almost
only related on bio monitoring.
Conclusions of the above results are limited
to low respondents on the questionnaire, but
150
* Considerable variations occur
1 Riley and Chester (1971)
2 Spotte (1992)according to - Bidwell and Spotte (1985), Mactyre (1976),Goldberg(1980) and Brewer (1975)
3 Natural Seawater Gulf of Biskaje, N 045 º,49,40’. W 007º,30,80’ (Sondervan, unpubl. results)
Table 4: Three references of important major, minor and trace elements in seawater (S=35 ‰)
Hydrogen H H2O 10,700 10,800
Chlorine Cl Cl-19,870 19,000
Sodium Na Na+11,050 10,500 10,880
Magnesium Mg Mg2+ 1,326 1,350 1,320
Sulphur S SO4
2-, NaSO4
-928 885 903
Calcium Ca Ca2+ 422 400 433
Potassium K K+416 380 407
Bromine Br Br-68 65 69
Carbon C HCO3
-, CO3
2-, CO228 28
Strontium Sr Sr2+ 8.5 8 7.17
Boron B B(OH)3, B(OH)4
-4.5 4.6
Silicon Si Si(OH)41* 3
Fluorine F F-, MgF+1.4 1.2
Nitrogen N N2, NO3
-, NO2
-, NH4
+, NH30.5 - 15 0.5 - 15
Lithium Li Li+0.18 0.17 0.176
Rubidium Rb Rb+0.12 0.12
Phosphorus P H2PO4
-, HPO4
2-, PO4
3- 0.07 0.07 0.04
Iodine I IO3
-, I-0.06 0.06 0.082
Barium Ba Ba2+ 0.03 0.03 0.008
Aluminium Al Al(OH)4
-0.005* 0.01 0.029
Iron Fe Fe(OH)2
+, Fe(OH)4
-0.003* 0.01 < 0.01
Molybdenum Mo MoO4
2- 0.010 0.01 0.001
Nickel Ni Ni2+ 0.002* 0.007 0.0032
Arsenic As HAsO4
2-, H2AsO4
-0.0023 0.003
Zinc Zn ZnOH+, Zn2+, ZnCO30.0050 0.01 0.131
Copper Cu Cu2+, CuOH+, CuCO30.0030 0.003 0.0101
Tin Sn SnO(OH)3
-0.00001* 0.0008 0.0005
Uranium U UO2(CO3)2
4- 0.0033 0.003
Chromium Cr Cr(OH)3, CrO4
2- 0.0006* 0.00005 0.001
Manganese Mn MnCl+, Mn2+ 0.0020 0.002 0.0394
Vanadium V H2VO4
-, HVO4
2-, VO3- 0.0015 0.002
Titanium Ti Ti(OH)40.0010 0.001 0.002
Cesium Cs Cs+0.0005 0.0003 0.003
Antimonium Sb Sb(OH)6- 0.0002 0.0003 <0.001
Silver Ag AgCl2
-, AgCl3
2- 0.00010 0.0003
Yttium Y Y(OH)30.00001 0.00001 < 0.001
Cobalt Co Co2+ 0.00008* 0.0004 0.001
Neon Ne Ne(gas) 0.00012 0.0001
Cadmium Cd CdCL2, CdCl+, Cd2+ 0.00005 0.00011 0.0002
Tungsten W WO4
2- 0.00012 0.0001
Selenium Se SeO3
2- 0.00045 0.00009
Element Species A1B2C3
mg.L-1 mg.L-1 mg.L-1
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
151
CH a P t e r 15: tr a C e e l e M e n t s , f u n C t i o n s , s i n k s a n d r e P l e n i s H M e n t in r e e f a q u a r i a
should not be ignored.
Another questionnaire (Sondervan and Causer,
in press) showed that 76.2 % of the European
aquariums measured their water quality daily,
88.1 % weekly and 42.9 % monthly or in
combination.
Table 5 gives a view which parameters are
measured in the European aquariums, only
7.1 % of the aquariums were measuring trace
or minor elements.
The similarity in both questionnaires is that
still less efforts have been made in measuring
trace elements. It is important to come to
a standard procedure that describes which
elements should be analyzed at aquariums
which have invertebrates and life corals in their
collections. When these results are completed
with information of present life support systems,
better knowledge will be obtained what really is
necessary for coral husbandry.
It’s advised to measure in any case the following
macro and trace elements in coral systems: K,
Ca, Mg, Sr, Fe, Si, Mo, Mn, I, Li, Al, Ti, Cr, Co,
Ni, Cu, Zn, Br and Ba on a regularly interval.
Trace elements in reef aquaria -
supplementation
In the natural environment corals, especially
scleractinian corals, meet their demand for
energy and nutrients from various sources with
a substantial portion that is met by the capture of
prey. In reef aquaria in most cases the portion of
heterotrophic nutrition of symbiotic scleractinian
corals is much lower and especially in regards
of trace elements an additional supplementation
may be indicated.
In the Jura-Museum, Eichstätt, where one of
the authors (Balling) worked from 1987 until end
of 2000 the rst Acropora corals where kept in
the early 90s. The problem of effective calcium
hydrogencarbonate supplementation was
already overcome by a three part calcium additive
published in 1994 (Balling, 1994). However the
growth of the Acropora corals seemed to be not
optimum since the new grown branches where
quite pale and thin. Considering the accepted
importance of trace elements in plant nutrition
the author started rst experiments on the
supplementation of trace elements for corals.
Especially the calcareous coral skeletons
seemed to be a major sink for trace elements.
The data published by Milliman (1974) showed
up the trace element concentrations of the
diverse marine carbonates. From these data
the amounts of trace elements that have to be
supplied to the aquarium to compensate for the
loss of trace elements that have been trapped
in the calcium carbonate skeletons of the corals
and corallinaceous algae have been calculated.
The recipe has been published together with
rst experiences with this kind of trace element
addition in 1996 (Balling, 1996 b).
Calculated from data from Milliman (1974) one
of the authors published the following trace
element recipe (Balling, 1996 b):
Solution 1
243.45 g SrCl2.6H2O; 356 mg BaCl2.2H2O;
make up with water to 1 L solution.
Solution 2
4 g FeSO4.7H2O; 185 mg MnSO4.H2O;
98 mg CuSO4.5H2O; 88 mg ZnSO4.6H2O; 89
mg NiSO4.6H2O; 324 mg CrCl3.6H2O;
4 mg CoCl2.6H2O;
make up with water to 1 L solution.
(10 ml of each solution is added to 2 L solution
of 143 g CaCl2.2H2O in water)
Solution 3
2.5 g KI; 13.3 g NaF;
make up with water to 1 L solution.
(10 ml of this solution is added to 2 L solution of
168 g NaHCO3 in water)
Parameter % Parameter % Parameter %
Salinity
Temperature
pH
Redox potential
Turbidity
95.2
97.6
97.6
95.5
14.3
Oxygen
Chloride
Ammonia
Nitrite
Nitrate
Phosphate
66.7
23.8
83.3
81.0
90.5
59.5
Calcium
Magnesium
Iodide
Bromine
Strontium
Trace/Minor elements
59.5
19.0
21.4
14.3
23.8
7.1
Table 5. Percentages of used analysis in European Aquariums
152
The application of trace elements according to
the recipe above led to better opening, good
continuous growth of corals and better colours.
The corals especially enhanced the green
uorescent colours. The corals returned to
natural more sturdy growth shapes.
After the onset of trace element supplementation
repeated expellings of zooxanthellae have been
observed which may be interpreted as attempts
of the corals to regulate internal trace metal
concentration but which may more probable be
attributed to enhanced algal cell division.
Shimek (2002) expects high mortality of corals
at elevated trace metal concentrations during
acclimation. In the time of the regular trace
element application, from 1994 until the end
of 2000, no problems with the acclimation of
freshly imported corals have been observed.
General biology of the aquaria supplemented
with trace elements was rich and diverse with
a good abundance of planktonic organisms
like copepods and polychaets. Occasionally
nocturnally captured polychaets could be
observed on large polyped stony corals in the
morning.
The green brittle star (Ophiarachna incrassata)
propagated repeatedly.
The proportions of trace elements (and nutrients
in general) seem to be more important than
the absolute concentration in a certain extent.
An advantage of a balanced trace element
supplementation with an elevated concentration
of all essential trace metals may be a higher
stability against imbalances caused by minor
accidental additions of just one trace element,
for example with contaminants.
The recipe given above has been republished
by Renke (1999) complemented with additional
molybdenum, strontium, iron and manganese
for better growth of corallinaceous algae and
again in 2001 (Renke, 2001) with additional
calculations.
This repeated publication of the recipe in
German aquariophilic newspapers and
homepages initiated the development of
several commercial trace element mixtures with
widespread use. The different commercial trace
element mixtures competed for the induction of
brighter colouring of corals which nally led to
a mode of trace element addition that induces
a controlled bleaching through temporary trace
metal stress.
Another technique to add trace elements is via
the medium in calcium reactors. Besides lime
(CaCO3) also coral sand can be used to dissolve
within a calcium reactor. Measurements of the
inuent and efuent at different pHs show there
is a consistant addition of strontium when using
1 to 2 cm large coral rubble as medium in a
calcium reactor (Figure 4) (Janse, unpublished
results). No conclusions can be taken from the
ICP-MS readings of the other trace elements
data. Possibly not all elements will dissolve
with the same ease as calcium and strontium.
The calcium and strontium ratio of average 45,
is in agreement with the ratio found in stony
coral skeleton.
Long term changes in strontium levels,
measured with ICP-OES in three coral systems
at Burgers’ Zoo, Arnhem, The Netherlands are
Figure 4: Differences in calcium and strontium concentration between the inuent and efuent of a calcium reactor at
Burgers’ Ocean, Arnhem, measured with an ICP-OES
CALCIUM INCREASE (mg Ca.L-1)
STRONTIUM INCREASE (mg Sr.L-1)
y = 45.028x - 7.3017
R2 = 0.8855
0.0 1.0 2.0 3.0 4.0
200
150
100
50
0
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
153
CONCENTRATION STRONTIUM (mg Sr2+.L-1)
6.000 L 16.000 L 750.000 L
AQUARIUM AGE (years)
0 2 4 6
14
12
10
8
6
CH a P t e r 15: tr a C e e l e M e n t s , f u n C t i o n s , s i n k s a n d r e P l e n i s H M e n t in r e e f a q u a r i a
displayed in Figure 5. Due to changes of the
articial salt from 7.2 mg Sr2+.L-1 in the rst
year to 8.5 mg Sr2+.L-1 in the later years the
strontium level increased towards a maximum
of 8.5 mg.L-1. Addition of a calcium rector (with
coral sand as medium) increases the strontium
level further. From year three the two smaller
systems had received twice a week extra
additions of a SrCl2.6H2O solution, which was
an addition of approximately 0.01 mg Sr2+.L-
1.d-1. The largest system received addition of
the same solution from year 5 on at an average
rate of 0.02 mg Sr2+.L-1.d-1.
Even though the water management and
stocking densities of corals differed between
the systems it’s clear that strontium addition
via a calcium reactor and chemical addition will
keep the strontium level between a predened
range of 10 to 12 mg Sr2+.L-1. When possible
the addition management can be changed
when the trace elements are measured on a
regular basis.
Trace elements in reef aquaria – chemical
speciation and toxicity
The chemical speciation is of central importance
for bioavailability and toxicity of trace metals
(De Haan, 1984).
Organic ligands that bind to the trace metals
alter the toxicity. Most trace metal complexes
are less toxic but also less bioavailable.
In need for iron and under competition for iron
the diverse organisms excrete different specic
ligands, so called siderophores that reduce
availability of complexed trace metal to other
organisms. Siderophore complexes of copper
differ from the siderophore complexes of iron
and the organisms can discriminate against the
copper complexes.
But organic substances can not only have a
moderating but also an enhancing effect on
trace metal toxicity. For example it was observed
that complexes of copper with citrate and with
nitrilotriacetate are more toxic to phytoplankton
than ionic copper.
The apparently unregulated way in which the
zooxanthellae take up copper in corals may be
attributed to such a mechanism.
Trace elements in reef aquaria –
bioindication
The most important bioindicators for the trace
element and nutrient status in the reef aquarium
are the corals. Thoroughly observed they are
good indicators of a healthy environment and
good growing conditions.
Deep brown opaque tissue where the
zooxanthellae are not covered by uorescent
pigments indicate high nutrients and moderate
light. Light brown colours and transparent tissue
indicate low nutrients nitrogen and phosphate
and/or strong illumination. Weak uorescent
pigmentation can indicate low trace element
concentration. Bleaching and excessive mucus
secretion can indicate trace metal intoxication.
Since different species and different clones
Figure 5: Strontium conentrations changes in three coral reef systems at Burgers’ Zoo, Arnhem, Netherlands. The
arrow indicates the addition of a calcium reactor to the specic aquarium system
154
of one species show different colours, it is
necessary to know the normal appearance of
a coral under the given culture conditions. With
the necessary sensibility for changes in the
appearance of the corals it is possible to react
to negative changes and developments in the
aquarium milieu.
The skeletons of corals can be used for the
monitoring of the trace metal concentration in
reef aquaria. Branches of colonies can easily
be broken by hand, protected with disposable
gloves. Different parts of the branches can be
taken as record of the trace metal concentrations
at the time they grew.
Fragments of corals grown in the Jura-Museum
under the trace elements supplementation
described above where analysed by the
Geological Institute in Munich. They showed
comparable trace element concentration as
wild caught corals which died during import.
However the variations in trace element
concentrations between different parts of the
same colony frequently showed the same
variation as the different colonies amongst
each other.
Also other invertebrate animals in the reef
aquarium can be good bioindicators. Sea
urchins, especially the species Diadema
antillarum is highly sensitive to heavy metal
pollution of the environment but also Diadema
setosum is a good bioindicator.
Intoxication by copper results in changes in
the behaviour of the sea urchin. D. antillarum
positions itself on the bottom of the tank
followed by spine closure at concentrations
below 10 µg.L-1 and 96-h LC 50 was 25 µg.L-1
(Bielmeier et al., 2005).
High concentrations of zinc (approximate
1,000 µg.L-1) caused death of brittle stars
(Ophiuroidea), feather stars (Comatuloidea)
and gammarids in a invertebrate system of the
Artis Aquarium, Amsterdam (Sondervan, 2004).
Scleractinian corals, sea urchins and other
invertebrates showed signs of intoxication but
were affected less severely.
Echinoderms show a high sensitivity to
contaminants due to the extensive contact to
the surrounding water via their ambulacrale
system.
Trace elements in reef aquaria – rst aid
measures and depletion at suspected trace
element intoxication
If corals show signs of trace element intoxication
the safest but not always practicable method to
lower the concentrations of toxic substances
are water changes. With salt and tempered
reverse osmosis water, water changes of
50 or 60 % are no problem for the inhabiting
corals and Tridacna clams. Other invertebrates
should tolerate such water changes too, but in
some like sponges or feather stars contact of
the animal to air should be avoided. Big water
changes are always benecial and always a
good rst aid measure for any problem related
to water quality. Regular water changes are an
important measure for continuous and good
water quality.
Trace metals are adsorbed to ferric oxides and
hydroxides. The addition of dissolved iron salts
like iron(II)-sulphate to the reef tank or ltration
through granular ferric oxide hydroxide is
another rst aid measure against trace metal
intoxications.
Many aquatic and marine organisms, like
cnidarians, bacteria, cyanobacteria and algae
react to copper intoxication by the excretion
of chelating substances (Clarke et al., 1987,
Mitchelmore et al., 2003, Kazy et al., 2002,
Gledhill et al., 1999), exopolysaccharides with
acidic groups like carboxyl groups. These
exopolysaccharides adsorb to air bubbles
(Zhou and Mopper, 1998) and can be removed
from the tank which is also an important export
mechanism in the regular running of a reef
tank. As can be expected from this conclusion
Shimek (2002) found high concentrations of
copper in skimmate. To support this kind of
export, exopolysaccharides and substances
with similar binding behaviour through
carboxyl groups can be added to the tank.
Good candidates are cellulose and cellulose
derivates, xanthan gum, carrageenan and
alginate. They are easily available in food
grade quality as thickening food additive. The
most promising one is alginate since its copper
binding activity has many times been tested
and described (Klimmek, 2003; Jang et al.,
2006; Cheng et al., 1992; Vieira and Volesky,
2000; Hameed, 2006) and one of the authors
(Balling) has tried the application of sodium
alginate as ne powder in reef aquaria himself
and considers this natural substance as safe.
Applied as powder the alginate does not
completely dissolve but partially settles down
on the bottom and can be removed from there
with a hose. If a sodium alginate solution is used
it must be thinned down to low concentrations
(<1 g.L-1) since thick sodium alginate solution
forms beads and lumps when poured into the
reef tank. This may be found out by trials at the
individual system.
H.-W. Ba l l i n g , M. Ja n s e & P.J. so n d e r v a n
155
CH a P t e r 15: tr a C e e l e M e n t s , f u n C t i o n s , s i n k s a n d r e P l e n i s H M e n t in r e e f a q u a r i a
Trace elements in reef aquaria – outlook
This article has tried to give some instructions
for the useful application and control of
trace elements in reef aquaria. With further
experiments, investigations and articles it will
be possible to control all nutrients in the reef
aquarium and adjust them at optimum levels
in the next years. This will be an important
step forward to keeping conditions as close to
nature as possible. This will make propagation
of corals by cuttings and fragments more
economic and perhaps sexual propagation in
captivity possible.
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