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Minimal research has been conducted on the geochemistry of acorn barnacles, yet recent studies suggest these sessile crustaceans have the potential to act as paleo-environment indicators, biomonitors of anthropogenic pollution, and tracers of marine megafauna movement. As there are nearly 900 species of acorn barnacles, it is necessary to investigate variations among species to determine their efficacy as proxies. The primary objective of this study is to compare trace metal concentrations of two extant barnacle species - Amphibalanus eburneus (ivory barnacle) and Semibalanus balanoides (northern rock barnacle) - to better understand their unique applications in the ocean sciences. Samples were collected from Manursing Island Club in Rye, New York, along the western shoreline of the Long Island Sound. Collected barnacles were photographed, and the rostro-carinal diameter of each specimen was measured to aid with identification. All barnacle plates were cleared of soft parts, sonicated in milli-Q water, brushed clean with vinegar, rinsed off, and soaked in bleach for 3 hours. Element/Ca ratios were measured using a ThermoScientific iCAPQ Quadrupole-Inductively Coupled Plasma-Mass Spectrometry (Q-ICP-MS). Li, Na, Mg, K, and Sr to Ca ratios were measured. A comparison of the K/Ca values of S. balanoides and A. eburneus was inconclusive. Additional data may be necessary to determine if there are interspecies differences within the same environment. However, Na/Ca, Li/Ca, and Sr/Ca ratios could be species-specific. S. balanoides was observed to have lower Na, Sr, and Li to Ca ratios than A. eburneus, although they were exposed to the same environmental conditions. Hence, any studies that wish to explore Na/Ca, Li/Ca, Sr/Ca in barnacles would need to target a given species or acknowledge potential offsets. Notably, S. balanoides samples collected downshore had lower Mg/Ca ratios than samples collected further upshore. This finding is not unsurprising as Mg/Ca values in barnacles have been known to be impacted by shore level. While the full extent of the utility of barnacle geochemistry is still undergoing exploration, we are just beginning to determine which potential proxies require species-specific investigations. 

The geochemistry of marine carbonates frequently reflects the environmental factors that influence their growth, such as climate and/or water quality. Barnacles are sessile crustaceans with shells that provide such environmental archiving. The bay barnacle, Amphibalanus improvisus, was found in the Hudson River at Piermont, NY and Nyack, NY and was the most abundant species identified. To expand the geographic perspective, Amphibalanus eburneus and Semibalanus balanoides barnacles were collected in Rye, NY on the Long Island Sound coast. However, this did not permit a perfect comparison as these species were not identified at the Hudson River sites. Barnacle samples were cleaned and organic matter removed with a multi-step process that included a vinegar scrub, short bleach bath, and ultrasonication in milli-Q water. Trace metals in calcium carbonate barnacle shells were analyzed via quadrupole mass spectrometer. The analysis focuses on Mg, Sr, Ba, Na, and Y to Ca ratios. There was geographic variation in barnacle Y/Ca, Ba/Ca, and Na/Ca values. This may indicate that the concentrations of these trace metals in the waters of the three places do vary, suggesting there could be potential to explore these measurements as an environmental proxy. The Mg/Ca and Sr/Ca inter-site variability was more difficult to quantify. Although Mg/Ca and Sr/Ca are known paleothermometers in other archives, more work needs to be done to determine their efficacy in these locations. Ultimately, this preliminary data and assessment shows that these metals can be recorded in barnacle shells and opens the door to future environmental- or climate-proxy development in the Hudson River and Long Island Sound.