Stable C and N isotope values in Kemp's Ridley sea turtle scutes in the northern Gulf of Mexico, 2010 to 2012

Following an explosion at the Deepwater Horizon drilling rig on April 20, 2010, MC252 an estimated 3.19 million barrels of oil leaked into the Northern Gulf of Mexico over 87 days. The endangered Kemp's ridley sea turtle (Lepidochelys kempii [Lk]) has a long established record of using the area near the well as primary foraging grounds. Resulting short- and long-term negative impacts of the oil spill on sea turtles could induce changes in the health and fitness of the Lk population. MC252 oil is known to have entered the foraging areas. Consequently, stable carbon and nitrogen isotope signatures from MC252 oil should be reflected in the food web and in the tissues of organisms such as sea turtles. We measured carbon and nitrogen isosope ratios of satellite-tagged turtles to 1) assess changes in foraging strategies of nesting Lk sampled in 2010 (the year of the spill) and two subsequent post-spill years; and 2) estimate the proportion of females that were within the area affected by the oil spill, the latter via discriminant analysis. Scute samples were collected using a biopsy punch from turtles nesting at a long-term study site on the Lower Texas Coast (Padre Island National Seashore) and on the Upper Texas Coast (Galveston Island to Surfside Beach). Turtles included in this study were sampled only once. δ13C values in samples obtained from turtles nesting in 2011 and 2012 were significantly depleted (F3,96=4.76, p=0.004 ) compared to 2010 samples. In contrast, there were no significant differences in δ15N among years. The depleted carbon values correlate with the depleted carbon values of MC252 oil. The distinctive isotope values of the satellite tagged females provided data with which to identify turtles that were inside the oiled area

2010年4月20日，深水地平线（Deepwater Horizon）钻井平台发生爆炸，此后MC252号油井在87天内累计向墨西哥湾北部泄漏约319万桶原油。濒危物种肯普氏丽龟（Lepidochelys kempii [Lk]）长期以来将该油井附近海域作为主要觅食场，已有明确的野外记录。此次漏油事件对海龟造成的短期与长期负面影响，可能会引发肯普氏丽龟种群的健康状况与生存适合度发生改变。现有研究证实MC252原油已侵入该觅食区域，因此其独特的碳、氮稳定同位素特征理应在食物网以及海龟等生物的组织中有所体现。本研究对卫星标记的海龟开展碳、氮同位素比值测定，以实现两大研究目标：其一，评估2010年（漏油发生当年）及后续两年漏油后产卵的肯普氏丽龟的觅食策略变化；其二，通过判别分析估算曾处于漏油影响区域内的雌性海龟占比。研究采用活检钻采集盾板样本，采样对象为德克萨斯州下海岸（帕德里岛国家海岸）以及上海岸（加尔维斯顿岛至冲浪滩）长期研究站点的产卵海龟。本研究涉及的所有海龟均仅接受一次采样。与2010年的采样样本相比，2011年与2012年采集样本的δ¹³C值显著贫化（F₃,₉₆=4.76，p=0.004）。与之相反，各年份间的δ¹⁵N值未呈现显著差异。这种碳同位素贫化特征与MC252原油的碳同位素特征高度吻合。卫星标记雌性海龟的独特同位素特征，可用于识别曾处于漏油影响区域内的个体。