Temporal and spatial variation in the δ¹⁵ N and δ¹³ C of coral tissue and zooxanthellae in Montastraea faveolata collected from the Florida reef tract

Abstract

Tissues were collected from Montastraea faveolata at five locations on the Florida Reef tract representing both nearshore and offshore environments. The tissue and zooxanthellae were removed from the skeletons, separated, and subsequently analyzed for ␦ 15 N and ␦ 13C. The mean ␦ 15N value in the coral tissue was ϩ6.6 (Ϯ0.6‰) while the ␦ 13 C was Ϫ13.3 (Ϯ0.5‰) (n ϭ 197). The ␦ 15 N and ␦ 13 C of the zooxanthellae were ϩ4.7 (Ϯ1.1‰) and Ϫ12.2 (Ϯ1.0‰), respectively (n ϭ 147). The differences in the ␦ 15 N and ␦ 13 C between the zooxanthellae and the tissue were statistically significant. No statistically significant differences were observed between nearshore and offshore stations in either ␦ 15 N or ␦ 13 C. The absence of a difference casts doubt on both whether the ␦ 15 N of the coral tissues is related to anthropogenic influences and/or whether the ␦ 15 N value itself can be used as an indicator of sewage contamination in corals. Between 1995 and 1997, there was an increase of 1‰ in the ␦ 13 C and a decrease of approximately 0.8‰ in the ␦ 15 N. The increase in the ␦ 13 C of the organic material was mimicked in the ␦ 13C of the skeletal material from corals from two reefs in the area. There appears to be clear seasonal variations in the ␦ 13 C of the coral tissue at certain locations with ␦ 13 C of the coral tissues and the zooxanthellae becoming more positive between July and August. The difference between the ␦ 13 C of the zooxanthellae and the coral tissue varies seasonally with the maximum difference occurring in July of each year. In contrast, the maximum ␦ 13 C in the skeleton appears to occur later in the year, between September and November.It is well established that certain scleractinian corals have symbiotic associations with dinoflagellate algae (zooxanthellae) that are beneficial to the host (Muscatine and Cernichiari 1969). The zooxanthellae are able to pass organic compounds to the coral, resulting in positive influences on the growth of the coral. Under shallow water conditions, the coral-zooxanthellae system is autotrophic (Muscatine and Cernichiari 1969). Evidence of the autotrophic nature of zooxanthellate corals is found in the difference in the ␦ 13 C of the zooxanthellae and coral tissue at various water depths. At shallow depths, where light intensity is high, the ␦ 13 C of the zooxanthellae and the coral tissue are relatively similar (Land et al. 1975;Muscatine et al. 1989) and the ␦ 13 C of the coral tissue is significantly more positive (Ϫ10‰ to Ϫ14‰) than the supposed food source of the coral, zooplankton (ϳϪ20‰). This indicates that sufficient photosynthate is being translocated so that the ␦ 13 C values of the coral tissue and zooxanthellae are similar. With increasing depth, the ␦ 13 C of the coral tissues become more negative and the ␦ 13 C approaches that of the zooplankton. Such variations are taken as indicating a change from autotrophy to heterotrophy.1 Corresponding author (pswart@rsmas.miami.edu). AcknowledgmentsThis field work was supported by an NURP grant and, in th...

The response of the scleractinian coralTurbinaria reniformisto thermal stress depends on the nitrogen status of the coral holobiont

“…Changes in δ 15 N of anthozoan and algal tissue are regularly used to track nitrogen sources in these organisms [see discussion by Swart et al (Swart et al, 2005)]. In the present study, the largest change was observed in the symbionts (−4‰), which are the main site of ammonium assimilation (Grover et al, 2002;Pernice et al, 2012).…”

Stable isotopes reveal limitations in C and N assimilation in the Caribbean reef corals Madracis auretenra, M. carmabi and M. formosa

“…These values are relatively low compared to other zooxanthellate coral species, which mostly range between -12 and -14 ‰ at the same depths (Muscatine et al 1989, Swart et al 2005, Alamaru et al 2009a), but similar values have been previously reported for M. auretenra (Muscatine et al 1989). Lower δ 13 C values can hint at lower photosynthesis and/or at faster replenishment of internal DIC from ambient seawater DIC due to reduced diffusion distances.…”

Nitrogen and oxygen isotopic signatures of subsurface nitrate seaward of the Florida Keys reef tract

“…3-4% indicate land-based nutrient pollution (Lapointe et al 2004). In the same region, however Swart et al (2005) found no clear signals in coral d 15 N from offshore to nearshore reefs but did find significant temporal variation, suggesting seasonal changes in the relative importance of coral autotrophy and heterotrophy.…”

“…With the use of discernable differences between d 15 N values for natural versus anthropogenic sources of nitrogen, a number of studies have investigated nitrogen pollution in coral reef environments via measurement of tissue d 15 N in benthic organisms (e.g., Sammarco et al 1999;Heikoop et al 2000;Swart et al 2005). Recognition of an isotopic signal from anthropogenic nitrogen in benthic organisms depends on clear differentiation of d 15 N in potential sources.…”