Causes of sulfur isotope variability in the seagrass, Zostera capricorni
نویسندگان
چکیده
Sulfur has been proposed as a useful element to employ in addition to carbon and nitrogen in stable isotope studies of marine food webs, but variability in dS of primary producers may prevent food web resolution. dS values in green leaves of the seagrass, Zostera capricorni, showed considerable variability (12.7–17.6x) in a survey in Moreton Bay, Australia. We demonstrated that dS values were correlated with sediment organic matter (OM) content and height of seagrass on the tidal gradient, but these relationships were opposite to those expected from work elsewhere. In our survey, dS values were relatively depleted at sites higher on the shore and with lower OM content. We did find the expected relationship of depleted dS values where sediment porewater sulfide concentrations were higher. Any influence of OM content on dS values would have been confounded in the survey by the relationship between height on shore and OM content itself. We separated the effects of height and OM content by creating the following treatments at one height on the shore: (1) OM added, (2) procedural control, and (3) untouched control. dS values of seagrass in OM added plots were significantly depleted (5.6x) relative to procedural (10.1x) and untouched (11.0x) controls 8 weeks after the manipulation. This demonstrated that OM content on its own does have the expected effect on dS values of seagrass, so in the initial survey another factor, probably related to height on shore, must have overridden the influence of OM content. Seagrass roots are able to exude excess oxygen produced during photosynthesis, reoxidising sulfides in surrounding porewater. We demonstrated that the above and below-ground biomass of seagrass 0022-0981/$ see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2003.10.011 * Corresponding author. School of Environmental and Applied Sciences, Griffith University, PMB 50, Gold Coast Mail Centre, Queensland, 9726, Australia. Tel.: +61-7-5552-8983; fax: +61-7-5552-8067. E-mail address: [email protected] (J.M. Oakes). J.M. Oakes, R.M. Connolly / J. Exp. Mar. Biol. Ecol. 302 (2004) 153–164 154 was higher low on the shore, and contend that higher seagrass productivity low on the shore results in greater reoxidation of sulfides and leads to more enriched dS values of seagrass. D 2003 Elsevier B.V. All rights reserved.
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