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

在日本冲绳群岛的一个海底洞穴中，栖息着高度和长度均小于3.5毫米的洞穴微型双壳类Carditella iejimens。放流和重新捕获调查的结果表明，该物种有可能经历全年持续的生长。如果这种解释是正确的，贝壳可能需要超过1年的时间才能达到1毫米的高度，需要4年才能达到3毫米的高度；因此，据估计，切济鱼的寿命至少为4年。为了评价该物种作为定量古海洋学指标的价值，我们分析了从海底洞穴中采集的60个活的裂殖吸虫标本的δ18O值。结果表明，大多数个体保存的δ18O值对应于年平均温度和海水的δ18O。这些结果，当应用于洞穴中的化石贝壳δ18O记录时，表明如果从过去7000年的古温度记录来看，最近的变暖可能是异常的，包括中世纪暖期和中全新世气候最佳时期。

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.