Evolution of life-history strategy and paleoclimate changes from an geochemical record of a cave-dwelling marine micro-bivalve.

在日本冲绳岛附近的海底洞穴中，栖息着一种高度和长度都不到3.5毫米的穴居微型双壳类Carditella iejimensis。放生和再捕获调查的结果表明，该物种有可能经历全年的连续生长。如果这种解释是正确的，那么外壳可能需要1年以上的时间才能达到1毫米的高度，4年才能达到3毫米；因此，依jimensis的寿命估计至少为4年。为了评估该物种作为定量古海洋学代用物的价值，我们分析了海底洞穴中采集的60个活C. iejimensis标本的δ18O值。结果表明，大多数个体保留了与年平均温度和海水δ18O相对应的δ18O值。将这些结果应用于该洞穴的化石壳δ18O记录，表明在过去7000年的古温度记录（包括中世纪温暖期和中全新世气候最佳期）的背景下，最近的变暖可能是例外的。

Cave-dwelling micro-bivalve Carditella iejimensis,which is less than 3.5 mm in height and length, inhabits the sediment surfacein a submarine cave off the Okinawa Islands, Japan. The result of mark-release and recapture surveys indicates that the species is potentially able to undergo year-round continuous growth. If this interpretation is correct, the shell probably requires more than 1 year to reach 1 mm in height, and 4 years to reach 3 mm; consequently, the lifespan for C. iejimensis is estimated to be at least 4 years. To evaluate the use of this species as a quantitative paleoceanographic proxy, we analyzed the δ18O values of 60 living C. iejimensisspecimens collected from the submarine cave. Results show that most individuals preserve δ18O values corresponding to the mean annual temperature and δ18O of seawater. These results, when applied to fossil shell δ18O records from the cave, indicate that the recent warming is likely exceptional, when viewed in the context of the past 7000 years paleotemperature record, which includes the Medieval Warm Period and the Middle Holocene Climatic Optimum.