Reproductive Ecology and Body Burden of Resident ... - The Love Lab

an undetectable amount of an isotope in a sample. The undetectable elements were Ag, Cd, Ce, Hg, U, V,
and Co. The isotopes of these elements were detectable in 10% or less of the otolith samples of each species
assayed in 21 sequences (Appendix 1). The twelve isotopes remaining on the assay panel were detectable in
36% to 100% of the otolith samples assayed.
Average detection limits for each element per sequence, calculated as 3 x SD of the intensity of 1%
HNO3 blanks and expressed as ratios of the isotope intensity and mean otolith Ca48 intensity, are given in
Appendix 1. We found that as few as 19% of the measurements of a single element in otoliths of one species
were above the detection limit.
We evaluated the suitability of the abundance datasets of each of 12 elements for inclusion in our
statistical analysis. We deemed Mg Ca -1 , Sr Ca -1 , Fe Ca -1 , Cu Ca -1 , and Ba Ca -1 suitable for our statistical comparisons
of kelp rockfish otolith element abundances. All of these elements were detectable in at least 80%
of the kelp rockfish otolith samples. In addition to these five element Ca -1 ratios, we included Mn Ca -1 in the
sanddab otolith element dataset for statistical analysis. In contrast to Mn Ca -1 which was detectable in 99%
of the otolith samples, Mn Ca -1 was excluded from the kelp rockfish otolith element dataset, because Mn Ca -1
was detectable in only 36% of the samples, and only 12% of the samples were above the detection limit. Although
otolith Fe Ca -1 was above the calculated detection limit in only 34% and 31% of the otolith samples
of kelp rockfish and sanddab, respectively, we included the element in our statistical comparisons because
of the high proportion (>80%) of detectable measurements (positive-valued, blank-corrected estimates).
Seawater preparation and microchemical analysis
Within 12 hours of collection, each seawater sample was run through a 0.22µm polyvinylidene fluoride
(PVDF) membrane (Millipore Steriflip vacuum filter unit). Each disposable, single-use filter unit and acidleached
receptacle vial were rinsed three times with ultrapure water (N-pure, resistivity>18.1 M cm) before
running a seawater sample through it. The filtrate was acidified with 1µm l ml -1 trace metal grade 12 mol
L -1 HCl to a target pH of 2-3. The acidified filtrate samples were individually stored in airtight plastic bags.
Sample filtering and acidification steps were performed under HEPA-filtered Class 100 laminar flow hoods,
except for seawater samples from sanddab collection sites in the Point Conception area and from sanddab
and kelp rockfish collection sites in the Southern California Bight area that were prepared under ordinary
indoor conditions without flow hoods.
Seawater samples were analyzed by staff at the Marine Science Institute Analytical Laboratory at University
of California, Santa Barbara. Different methods and instruments were used to determine the concentrations
of a suite of elements in seawater. Seawater Ba and U analyses were performed using the method of
isotope dilution with all samples run on the Element 2 ICP-MS. Enriched 135 Ba and 235 U standards of known
isotopic abundance and concentration were added to each sample. 135 Ba/ 138 Ba and 235 U/ 238 U ratios were measured,
mass bias corrected, and used to calculate the amount of natural Ba and U present in the samples
at natural isotopic abundances. Mg, Ca, and Sr analyses were performed using the method of standard additions
with all samples run on a Varian AA240FS fast sequential atomic absorption spectrometer. Spiked
samples served as standards, because it is difficult to matrix match seawater. A calibration curve based on
samples spiked to three levels of analyte concentration was used to estimate the element concentration in
the seawater samples with the assumption that the matrix of the seawater samples and spiked seawater are
the same. All seawater samples also were run on the Element 2 ICP-MS to collect selected isotopes using
the method of standard additions and internal standard to correct for instrument drift. Indium-115 ( 115 In)
was used as the internal standard for the following isotopes (run in low resolution): 109 Ag, 114 Cd, 133 Cs, 140 Ce,
202
Hg, 206 Pb. Scandium-45 ( 45 Sc) was used as the internal standard for the following elements, which were
run in medium resolution (isotopes collected are listed): 27 Al, 51 V, 52 Cr, 55 Mn, 56 Fe, 59 Co, 63 Cu, 66 Zn.
39