Experimental growth pattern calibration of Antarctic scallop shells ( Adamussium colbecki, Smith 1902) to provide a biogenic archive of high-resolution records of environmental and climatic changes

Abstract

To determine the potential of Antarctic bivalve shells as biomonitors for environmental and climatic variations in polar marine areas, we developed a growth model for juvenile Adamussium colbecki Smith, 1902 based on the use of in situ temporal calcein markings to calibrate growth patterns in the external striae formation. To minimize scallop stress caused by excessive handling, in situ benthic chambers were used for the marking experiment, during an exposure time of 6 h. Once marked, scallops remained on site in a benthic cage and were collected 18, 26, and 41 days later. Apart from a few specimens affected by possible calcein toxicity effects, the detectable mark in all shells revealed a higher austral summer growth rate for A. colbecki compared to other Antarctic bivalves. Using calcein labeling, we identified a near 14-day periodicity in the striae formation associated with the fortnightly seawater level regime. Striae counting and increment width measurements showed an annual cycle, with no clear cessation of growth in juvenile specimens, allowing age determination. Because of the relatively high growth rate for a polar species and easily recognizable sclerochronological calendar in the shell striae formation, A. colbecki is an appropriate species for high-resolution (infra-monthly) geochemical sampling. Comparison between LA-ICP-MS analyses (Li, B, Mg, Mn, Co, Sr, Ba, Pb) from one shell and hydrological parameters (sea level, temperature, salinity) measured in seawater suggests, however, that more work is needed to calibrate the trace element proxies. Nevertheless, the shell of the Antarctic scallop A. colbecki has tremendous potential for recording environmental conditions from time periods covering months to a few years in polar waters, notably the ice melting date.