Nitrogen fixation rates in algal turf communities of a degraded versus less degraded coral reef
- 547 Downloads
Algal turf communities are ubiquitous on coral reefs in the Caribbean and are often dominated by N2-fixing cyanobacteria. However, it is largely unknown (1) how much N2 is actually fixed by turf communities and (2) which factors affect their N2 fixation rates. Therefore, we compared N2 fixation activity by turf communities at different depths and during day and night-time on a degraded versus a less degraded coral reef site on the island of Curaçao. N2 fixation rates measured with the acetylene reduction assay were slightly higher in shallow (5–10-m depth) than in deep turf communities (30-m depth), and N2 fixation rates during the daytime significantly exceeded those during the night. N2 fixation rates by the turf communities did not differ between the degraded and less degraded reef. Both our study and a literature survey of earlier studies indicated that turf communities tend to have lower N2 fixation rates than cyanobacterial mats. However, at least in our study area, turf communities were more abundant than cyanobacterial mats. Our results therefore suggest that turf communities play an important role in the nitrogen cycle of coral reefs. N2 fixation by turfs may contribute to an undesirable positive feedback that promotes the proliferation of algal turf communities while accelerating coral reef degradation.
KeywordsAlgal turf Benthic cyanobacteria Coral reefs Nitrogen cycle N2 fixation
We thank the reviewers for their helpful comments on the manuscript. We are most grateful to Hannah Brocke of the Max Planck Institute for Marine Microbiology for her help with the field incubations, Verena Brauer and Pieter Slot of the University of Amsterdam for their help with the gas chromatographic analyses, and Jan van Ooijen of the Royal Netherlands Institute for Sea Research (NIOZ) for the nutrient analyses. This research was funded by the European Union Seventh Framework Programme (P7/2007–2013) under Grant Agreement No. 244161 (Future of Reefs in a Changing Environment), and the Schure-Beijerinck-Popping Fund (SBK/JK 2011-31 KNAW, the Netherlands).
- Berman T, Bronk DA (2003) Dissolved organic nitrogen: a dynamic participant in aquatic ecosystems. Mar Ecol Prog Ser 31:279–305Google Scholar
- Burke L, Reytar K, Spalding M, Perry A (2011) Reefs at risk revisited. World Resources Institute, Washington, D.C. 130 ppGoogle Scholar
- Casareto BE, Charpy L, Langlade MJ, Suzuki T, Ohba H, Niraula M, Suzuki Y (2008) Nitrogen fixation in coral reef environments. Proc 11th Int Coral Reef Symp 2:890-894Google Scholar
- Grasshoff K, Ehrhardt M, Kremling K (1983) Methods of seawater analysis. Verslag Chemie pp 1:419 ppGoogle Scholar
- Hanson RB, Gundersen KR (1976) Bacterial nitrogen fixation in a polluted coral reef flat ecosystem, Kaneohe Bay, Oahu, Hawaiian Islands. Pac Sci 30:385–393Google Scholar
- Koop K, Booth D, Broadbent A, Brodie J, Bucher D, Capone D, Coll J, Dennison W, Erdmann M, Harrison P, Hoegh-Guldberg O, Hutchings P, Jones GB, Larkum AWD, O’Neil J, Steven A, Tentori E, Ward S, Williamson J, Yellowlees D (2001) ENCORE: the effect of nutrient enrichment on coral reefs. Synthesis of results and conclusions. Mar Pollut Bull 42:91–120PubMedCrossRefGoogle Scholar
- Porra RJ, Thompson WA, Kriedemann PE (1989) Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: verification of the concentration of chlorophyll standards by atomic absorption spectroscopy. Biochim Biophys Acta 975:384–394CrossRefGoogle Scholar
- Zuckermann H, Staal M, Stal LJ, Reuss J, Te Lintel HS, Harren F, Parker D (1997) On-line monitoring of nitrogenase activity in cyanobacteria by sensitive laser photoacoustic detection of ethylene. Appl Environ Microb 63:4243–4251Google Scholar