Lol
Here’s some:
Organisms That Use Strontium: Acantharia
One of the main users of strontium in the ocean are the
Acantharia.4, 9-16 These beautiful, free floating unicellular microorganisms are
related to radiolaria. They have radiating spines of strontium sulfate that are largely external to the central cytoplasm. Inside the “body”, the spines are connected. The end result is something that
looks like a microscopic sea urchin.
Acantharia live in the upper regions of the oceans where they deposit their strontium sulfate skeletons. Presumably, these skeletons are protected from dissolution somehow, perhaps with an organic coating as the radiolarian
Sphaerozoum punctatumdoes, described in the next section. When Acantharia die and sink, the protection of the strontium sulfate is lost, exposing the strontium sulfate to the open water, resulting in dissolution. They are populous enough that they are an important part of the strontium cycle in the oceans (which also includes river and hydrothermal vent input), taking strontium from the surface and delivering it to depths of up to 900 m, where most have completely dissolved.14,15
Are there Acantharia in
reef aquaria? I don’t know. In aquaria that use natural seawater they might be seeded into the
aquarium every time there is a water change. If there are appreciable numbers in some aquaria, then they might well provide a significant sink for strontium in those aquaria. In fact, they could cause rapid depletion of strontium. In other aquaria, for example those that use heavy skimming and artificial salt water, the likelihood that they are present in important numbers is likely much smaller. This potential difference between aquaria is one of many ways that the strontium balance may vary between different aquaria.
Organisms That Use Strontium: Radiolaria
Certain species of radiolaria also use strontium sulfate, despite having silica skeletons. The radiolarian
Sphaerozoum punctatum, for example, release flagellated swarmers during reproduction which contain crystals of strontium sulfate (celestite).17-19 These crystals are deposited inside a cytoplasmic vacuole, and have a 50-100 nm thick coating of organic material on it. This coating may reduce the likelihood of dissolution of the celestite, and may be a clue as to how the Acantharia keep their strontium sulfate spines from dissolving. What purpose these crystals serve to the
S. punctatum is unknown, but it may be an antipredatory defense.
Organisms That Use Strontium: Gastropods
Some gastropods, such as the sea slug
Aplysia californica, have a clearly defined requirement for strontium in the water. When they are grown in artificial seawater lacking strontium, they develop deformed shells and statocysts (that lack a statolith).20
Statocysts are balance organs in many invertebrates. They consist of a fluid-filled sac containing statoliths that stimulate sensory cells and help indicate position when the animal moves. Statoliths themselves are small solid granules, and are made largely of calcium carbonate in
Aplysia californica.
These organisms are quite sensitive to reductions in strontium, with a drop of only 1 ppm causing a detectable difference in development. For this organism there is a critical window of strontium exposure around day 4 of its life. Strontium added after that point cannot make up for the poorly developed statolith, which causes erratic swimming.
How exactly the strontium is used in the deposition of shells and the statolith is not known, but it is apparently somehow related to calcification.21 The statoliths of
A. californica raised in normal seawater have been shown to contain elevated strontium.22 In the absence of strontium, the calcification is decreased by 80%. At low strontium levels, calcification was not significantly reduced, but the shell and statolith were still defective. These researchers concluded “Although the role of strontium in embryonic calcification of
A. californica remains enigmatic, these data suggest that strontium affects a highly discrete regulatory component because these more general indicators of calcification and differentiation are unaffected by its absence.”
Organisms That Use Strontium: Cephalopods
As in
Aplysia californica, strontium appears to be important to the development of at least 7 species of cephalopod.23,24 In all of these, the aragonite statolith develops properly in artificial seawater containing 8 ppm strontium, but not in artificial seawater from which strontium is absent. The end result for cephalopods raised in seawater lacking strontium is uncontrolled swimming due to the poor statolith development. For cuttlefish (
Sepia officinalis ) the cuttlebone also develops improperly in the absence of strontium.
