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Journal article
Subtropical seagrass epiphytes: Nitrogen fixation rates align with Crocosphaera‐like cyanobacteria abundances
Limnology and oceanography, Vol.online ahead of print
11/17/2025
Web of Science ID: WOS:001615338200001
Abstract
Nitrogen fixers can enhance nitrogen availability for seagrass communities that may be nitrogen limited. However, the role of epiphytic diazotrophs, particularly cyanobacteria, in seagrass communities is not well understood. We measured nitrogen fixation rates, epiphyte biomass, and relative abundances of epiphytic diazotrophs on the leaves of Thalassia testudinum and Halodule wrightii in the northern Gulf of Mexico. Greater accumulation of epiphyte biomass and diazotrophs may occur in T. testudinum due to lower leaf turnover than found in H. wrightii , particularly during periods of seagrass dormancy. Nitrogen fixation rates were determined using the acetylene reduction assay, while quantitative polymerase chain reaction was used to measure relative abundances of three cyanobacterial diazotroph groups in epiphyte DNA. Nitrogen fixation and epiphyte biomass were higher on T. testudinum leaves than on H. wrightii leaves. The lowest average fixation rates occurred in August when leaf turnover was high. Three phylotypes of nifH genes were detected in most samples, but overall, Crocosphaera ‐like Group B cyanobacteria (UCYN‐B) were present on all leaves during all seasons. Relative abundance of this group was positively correlated with nitrogen fixation rates on both species ( r = 0.59, p = 0.02). At one of the four study sites, heterocystous cyanobacterial symbionts in the Richelia‐ like (Het‐1) and Calothrix‐ like (Het‐3) groups accounted for similar relative abundances to those observed with UCYN‐B nifH genes. Because T. testudinum and H. wrightii are dominant in shallow tropical and subtropical ecosystems, understanding the role that diazotrophic epiphytes play in providing nitrogen to these vital ecosystems is critical.
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Details
- Title
- Subtropical seagrass epiphytes
- Publication Details
- Limnology and oceanography, Vol.online ahead of print
- Resource Type
- Journal article
- Publisher
- John Wiley & Sons, Inc.; HOBOKEN
- Number of pages
- 14
- Grant note
- UWF Center for Environmental DiagnosticsUWF Graduate School
We thank Anthony Alberda, Madison Harvey, Barbara Albrecht, Morgan Armstrong, Alex Asiala, DJ Johnson, and the University of West Florida Marine Services Center staff for their assistance with field sampling and laboratory experiments. Christopher Pomory provided advice on statistical analyses. Isabella Orrantia Marmol helped with the optimization of qPCR conditions and with field work. We thank Amber Hardison for her insights and opinions about study design and Mike Murrell for assistance with ImageJ. We appreciate reviews of an earlier version of this manuscript by Tim Hollibaugh and Rachel Presley. This research was supported by the UWF Center for Environmental Diagnostics and Bioremediation and the UWF Graduate School.
- Copyright
- © 2025 The Author(s).
- Identifiers
- WOS:001615338200001; 99381552488606600
- Academic Unit
- Biology; Center for Environmental Diagnostics and Bioremediation ; Hal Marcus College of Science and Engineering
- Language
- English