Link between variation in skeletal isotopes (C,O) and tissue stable isotopes (C,N) of holobiont, polyp and zooxanthellae from coral colonies of Madracis spp
Abstract
The branching corals M. mirabilis, M. carmabi and M. formosa are abundant species in reefs of Curaçao (Netherlands Antilles). The species are adapted to different depths, growing in shallow (<20 m), intermediate (∼30 m) and deep waters (>40 m), respectively. With increasing water depth, a shift from a strongly autotrophic to a more heterotrophic life style can be expected. This should be detectable in both skeletal and tissue isotopes. If coral metabolism is mainly supplied by photosynthesis, the δ13C of zooxanthellae and polyp tissue should be the same indicating a complete carbon recycling between algal symbiont (zooxanthellae) and coral host. For the skeleton two major trends were observed for both oxygen and carbon stable isotopes: 1) values got heavier with increasing water depth and 2) values were more depleted at the fast growing colony tips than at the slow growing shaded side or base of a colony. We found large intra-colony variations of the skeletal δ13C signal within colonies of the deep-adapted coral M. formosa, with low δ13C signals being comparable to those of the shallow water coral. For the tissue the δ13C values of the holobiont ranged from -16.5 permil at shallow to -22 permil for the deep corals. At tips of colonies the tissue δ13C of zooxanthellae was heavier than the δ13C of the polyp tissue. Surprisingly, the magnitude of this offset was consistent over the whole depth range. Expected was that the difference in δ13C between zooxanthellae and polyp should increase with increasing water depth reflecting a shift from autotrophy to heterotrophy. The overall decrease in tissue δ13C with increasing depth hints at increased heterotrophic feeding, with the rate of carbon recycling between polyp host and symbiont being maintained over this depth gradient. On intra-colony scale (between tip and side of a colony), the tissue δ13C only differs by 0.5 permil and this difference is consistent at all depths (and hence the same for all species). This means there is little variation in tissue δ13C within a colony, compared to variation in skeletal δ13C of M. formosa (range 6 permil). It appears that metabolic changes on intra-colony scale fail to explain the enormous range in skeletal δ13C within the deep coral M. formosa. However, strong intra-colony variation of tissue δ15N in M. formosa may hint at a shift in the trophic relation even on intra-colony scale.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....2554M