Host-influenced geochemical signature in the parasitic foraminifera <i>Hyrrokkin sarcophaga</i>

<p><i>Hyrrokkin sarcophaga</i> is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam <i>Acesta excavata</i> and the scleractinian coral <i>Desmophyllum pertusum</i> (formerly known as <i>Lophelia pertusa)</i>. Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS).</p> <p>Our results reveal that the geochemical signature of <i>H. sarcophaga</i> depends on the host organism it infests. Sr <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="1b4178c77ca0d4bfee6c9ddd864f3a43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-4733-2021-ie00001.svg" width="8pt" height="14pt" src="bg-18-4733-2021-ie00001.png"/></svg:svg></span></span> Ca ratios are 1.1 mmol mol<span class="inline-formula">⁻¹</span> higher in <i>H. sarcophaga</i> that infest <i>D. pertusum</i>, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of <i>D. pertusum</i> has a naturally higher Sr concentration compared to the calcite of <i>A. excavata</i>. Similarly, we measure 3.1 ‰ lower <span class="inline-formula"><i>δ</i>¹³</span>C and 0.25 ‰ lower <span class="inline-formula"><i>δ</i>¹⁸</span>O values in <i>H. sarcophaga</i> that lived on <i>D. pertusum</i>, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO<span class="inline-formula">₂</span> hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="073414a2b77546d8d5847ae97897d626"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-4733-2021-ie00002.svg" width="8pt" height="14pt" src="bg-18-4733-2021-ie00002.png"/></svg:svg></span></span> Ca ratios in foraminifera that lived on <i>A. excavata</i> but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions.</p> <p>While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="36bd7baae116a5efc17e692d563c2b51"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-4733-2021-ie00003.svg" width="8pt" height="14pt" src="bg-18-4733-2021-ie00003.png"/></svg:svg></span></span> Ca, Mn <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="fb147fccdcf98a9911cf3d26a8f6dc33"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-18-4733-2021-ie00004.svg" width="8pt" height="14pt" src="bg-18-4733-2021-ie00004.png"/></svg:svg></span></span> Ca, <span class="inline-formula"><i>δ</i>¹⁸</span>O or <span class="inline-formula"><i>δ</i>¹³</span>C unless the host organism is known and its geochemical composition can be accounted for.</p>