Age and growth of Astarte borealis (Bivalvia) from the southwestern Baltic Sea using secondary ion mass spectrometry

Abstract

Traditional isotope sclerochronology employing isotope ratio mass spectrometry has been used for decades to determine the periodicity of growth increment formation in marine organisms with accretionary growth. Despite its well-demonstrated capabilities, it is not without limitation. The most significant of these being the volume of carbonate powder required for analysis with conventional drill-sampling techniques, which limit sampling to early in ontogeny when growth is fast or to species that reach relatively large sizes. In species like Astarte borealis (Schumacher, 1817), a common component of Arctic boreal seas, traditional methods of increment analysis are difficult, because the species is typically long-lived, slow growing, and forms extremely narrowly spaced growth increments. Here, we use Secondary Ion Mass Spectrometry (SIMS) to analyze δ 18 O in 10-μm-diameter spots and resolve the seasonal timing of growth increment formation in Astarte borealis in the southeastern Baltic Sea. In the individaul sampled here, dark growth increments can form in either the fall, winter, or spring. Furthermore, growth increment data from two populations (RFP3S = 54.7967° N, 12.38787° E; WA = 54.86775° N, 14.09832° E) indicate that in the Baltic Sea, A. borealis is moderately long-lived (at least 43 years) and slow growing (von Bertalanffy k values 0.08 and 0.06). Our results demonstrate the potential of A. borealis to be a recorder of Baltic Sea seasonality over the past century using both live-and dead-collected shells, and also the ability of SIMS analysis to broaden the spectrum of bivalves used in sclerocrhonological work.

Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

“…SIMS analysis was performed at the University of Wisconsin-Madison WiscSIMS laboratory on a Cameca IMS 1280 in August 2018 during the same session as Moss et al (2021) and following settings described in Wycech et al (2018). Analysis pits ~10 mm in diameter and ~1 mm deep were sputtered using a 1.0 nA primary beam of 133 Cs + .…”

“…The middle microstructural layer was targeted for SIMS analysis per Moss et al (2021). SIMS analysis started nearest the umbo and proceeded along growth direction to the growth margin, sampling nearly the entire lifespan of the specimen and yielding 482 SIMS d 18 O shell values.…”

“…Most dark increments occur at or near the highest SIMS d 18 O shell values (darker shades of blue circles locating SIMS pits on the shell cross-section in Figure 1A). Assuming one light/dark couplet represents an annual cycle, as is often the case in this species (Moss et al, 2018;Moss et al, 2021), our sampling interval equates to sub-monthly resolution on average (see Section 4.1 for further discussion of age modeling). However, we note that each discrete sample constitutes a 10 mm spot and a ~5 mm space between spots, and thus one-third of the shell along the sampling path is not represented by the samples presented in this study.…”

“…Based on previous work, A. borealis from the White Sea, Russia, reached 33.5 mm in length and allowed for traditional micromilling techniques (Moss et al, 2018). However, in a subsequent study, Moss et al (2021) found that A. borealis from the Baltic Sea is smaller than individuals from the White Sea, precluding the use of traditional micromilling techniques. Thus, they employed secondary ion mass spectrometry (SIMS) to allow for a horizontal sampling resolution of 10 mm with a sampled mass of approximately a nanogram, orders of magnitude smaller than traditional micromilling techniques and IRMS analysis.…”

“…Astarte borealis (Schumacher, 1817) is a common constituent of many Arctic and boreal seas, and individuals are reported to live for several decades (Moss et al, 2018;Moss et al, 2021) to over a century (Torres et al, 2011;Reynolds et al, 2022). Such long lifespans are not uncommon for high-latitude species.…”