ABSTRACT

Nitrogen and carbon are commonly used to determine nutrient regimes and trophic structures within marine ecosystems. Macroalgae are convenient for assessing nutrient conditions via stable isotopes and tissue nutrient levels because of their ability to absorb and integrate ambient nutrients over extended time periods. Calcified macroalgae, such as Halimeda and Udotea spp, are common constituents of tropical marine ecosystems, making them ideal candidates for nutrient-based and food web analyses. However, calcified genera require acidification to remove calcium carbonate to accurately determine δ¹³C and percentage of N (by weight); the overall effect of acidification on the tissue nutrients and stable isotopes of calcified genera is unresolved. Individuals of Halimeda kanaloana (n = 10) and Udotea geppiorum (n = 9) were collected from Maui, O‘ahu, and Lāna‘i. Each specimen was split into two samples and either decalcified using liquid-phase HCl (acidified) or left unaltered (control). We found that liquid-phase HCl acidification resulted in significantly lower percentage of N in both Halimeda kanaloana and Udotea geppiorum. Whereas δ¹³C values in acidified samples of both species were predictably lowered, the δ¹⁵N in acidified U. geppiorum was significantly increased. Acidification may have unpredictable consequences on both the percentage of nutrients in calcified algal tissue and their δ¹⁵N, suggesting that the use of acidification in calcified algal nutrient studies may produce erroneous conclusions. Analysing two sets of samples as calcified (for δ¹⁵N) and acidified (for δ¹³C) would eliminate these errors. However, the use of calcified macroalgae to assess percentage of N should be avoided.

摘要

氮和碳通常用于确定海洋生态系统中的养分状况和营养结构。大型藻类通过稳定的同位素和组织营养素水平可以方便地评估营养素状况，因为它们能够长时间吸收和整合周围的营养素。钙化大型藻类（例如Halimeda和Udotea spp）是热带海洋生态系统的常见组成部分，使其成为基于营养物和食物网分析的理想选择。然而，钙化属要求酸化准确地除去碳酸钙来确定δ ¹³ C和的N（按重量计）的百分比; 酸化对钙化属的组织营养和稳定同位素的总体影响尚未解决。个人Halimeda kanaloana（n  = 10）和Udotea geppiorum（n  = 9）分别来自毛伊岛，瓦胡岛和拉奈岛。将每个样品分成两个样品，并使用液相HCl脱钙（酸化）或保持不变（对照）。我们发现液相HCl酸化导致Halimeda kanaloana和Udotea geppiorum中的N含量显着降低。而δ ¹³这两个物种的酸化样品中的C值被可预测地降低时，δ ¹⁵ N的酸化U. geppiorum显着增加。酸化可能对钙化藻类组织营养成分的百分比和他们δ不可预料的后果¹⁵ N，这表明使用酸化钙化藻类营养的研究可能会产生错误的结论。分析两组样品作为钙化（对于δ ¹⁵ N）和酸化（对于δ ¹³ C）将消除这些错误。但是，应避免使用钙化大型藻类来评估N的百分比。