Blue Mussel Stable Isotope Analysis on Islands of the Virginia Coast

Blue Mussel Stable Isotope Analysis on Islands of the Virginia Coast As climate change causes ocean temperatures to rise, some intertidal organisms, like blue mussels ( Mytilus edulis ), are retreating northward. Species that consume blue mussels, like the federally-threatened red knot ( Calidris canutus rufa ), may be negatively affected by this range contraction. We investigated the variation in blue mussel abundance from 2010 - 2018 on Virginia's barrier islands, where migrating red knots eat recently settled blue mussels, and compared the oxygen isotopic composition of blue mussel shell calcite (delta^18O c ; n = 74) to delta^18O c , which is calculated to be in equilibrium with regional ocean water, to predict their origins. During peak red knot migration (May 14 - 27), between 34 - 538 blue mussels were available/core sample, with blue mussel abundance decreasing over time. Stable isotope analyses indicated that shell umbo delta^18O c (mean = -0.23o/oo, SE = 0.12) was more ^18O enriched than shell edge delta^18O c (mean = -0.53 o/oo, SE = 0.10). Blue mussel umbo delta^18O c was not different than the range of delta^18O c calculated in equilibrium with regional ocean water off the Virginia and Delaware coasts. Umbo delta^18O c was more ^18O enriched than the expected estuarine signature at the Delaware Bay's mouth, precluding an estuarine origin, and more ^16O enriched than the expected delta^18O c off New Hampshire's coast, likely precluding an origin that far north. We concluded that Virginia's juvenile blue mussels likely originated in the regional ocean between the Delaware Bay and Virginia. Continued increases in regional sea surface temperature may further affect the availability of blue mussels to foraging red knots in Virginia.弗吉尼亚海岸群岛蓝贻贝稳定同位素分析 随着气候变化导致海洋温度上升，部分潮间带生物如蓝贻贝（Mytilus edulis）正向北退缩。以蓝贻贝为食的物种，如联邦受威胁的红腹滨鹬（Calidris canutus rufa），可能会受到这种分布范围收缩的负面影响。本研究调查了2010-2018年间弗吉尼亚障壁岛上的蓝贻贝丰度变化——迁徙中的红腹滨鹬在此捕食新近定居的蓝贻贝，并将蓝贻贝壳体方解石的氧同位素组成（δ¹⁸O_c；n=74）与根据区域海水平衡条件计算得到的理论δ¹⁸O_c进行对比，以推断其起源地。在红腹滨鹬迁徙高峰期（5月14日-27日），每个核心样本可获取34-538只蓝贻贝，且蓝贻贝丰度随时间推移呈下降趋势。稳定同位素分析结果显示：壳体壳顶（umbo）处的δ¹⁸O_c平均值为-0.23‰，标准误（SE）为0.12，其¹⁸O富集程度高于壳体边缘处的δ¹⁸O_c（平均值为-0.53‰，标准误为0.10）。弗吉尼亚与特拉华海岸区域海水平衡状态下的δ¹⁸O_c范围与蓝贻贝壳顶处的δ¹⁸O_c无显著差异。壳顶处的δ¹⁸O_c较特拉华湾河口的预期同位素特征更为富集¹⁸O，因此排除了其河口起源的可能性；同时其¹⁶O富集程度高于新罕布什尔州海岸的预期δ¹⁸O_c，大概率也排除了其起源于该远北区域的可能。本研究推断，弗吉尼亚海域的幼年蓝贻贝大概率起源于特拉华湾至弗吉尼亚之间的区域海洋。区域海表温度的持续升高可能进一步影响弗吉尼亚地区觅食红腹滨鹬可获取的蓝贻贝资源量。