δ15N AND TISSUE NITROGEN CONTENT OF HAWAIIAN MACROALGAE FROM SHALLOW-WATER REEFS AND MESOPHOTIC CORAL ECOSYSTEMS
Loading...
Date
Authors
Strait, Nicholas
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
The Hawaiian Archipelago has a high abundance and diversity of macroalgae. These photosynthetic organisms, found from the intertidal to mesophotic depths, absorb nutrients and fractionate nitrogen based on point and non-point sources. The goal of this work was to improve our understanding of the nutrient sources within shallow-water and mesophotic coral ecosystems (MCEs) using compositional patterns of the stable isotope δ15N and percent nitrogen (%N) in macroalgal tissue. Calcified macroalgae require the removal of calcium carbonate to accurate determine δ13C and %N (by weight). Thus, I also analyzed the impact of acidification on calcified macroalgal stable isotopes and tissue nitrogen. The Main Hawaiian Islands (MHI) had significantly lower δ15N (with a few outliers > 7‰), while the protected Northwestern Hawaiian Islands (NWHI) had significantly lower %N. δ15N and %N differed between shallow and mesophotic depths within the MHI, while only δ15N differed in the NWHI. Macroalgae from the MHI had δ15N < 0‰ and > 7‰, and %N > 2.0%, suggesting anthropogenic N within both habitats. The data supports the hypothesis that near shore/shallow-water processes may influence the nutrients in MHI MCEs, as well as nutrient upwelling into MCEs within the NWHI. I also examined the difference in nitrogen content of psammophytic and saxicolous macroalgae and found that psammophytic genera have significantly higher %N. Liquid-phase HCl acidification resulted in significantly lower %N in both Halimeda kanaloana and Udotea geppiorum, suggesting that acidification is not advised when analyzing nitrogen in calcified algal tissue. My findings further the understanding of how anthropogenic nutrients may influence mesophotic habitats near populations centers such as the MHI.