 |
| Titel |
Estimation of internal and external nitrogen for corals with a long-term 15N-labelling experiment and subsequent model calculations |
| VerfasserIn |
Yasuaki Tanaka, Andréa Grottoli, Yohei Matsui, Atsushi Suzuki, Kazuhiko Sakai |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250094169
|
| Publikation (Nr.) |
 EGU/EGU2014-9565.pdf |
|
|
|
|
|
| Zusammenfassung |
| Coral reef ecosystems maintain high primary productivity though the seawater is extremely
oligotrophic. One of the hypotheses to explain this paradox is the recycling of nutrients in
animal-algal symbiotic organisms such as corals. It is relatively easy to measure nutrient
uptake rates by corals from seawater, but the proportion of internally circulating nutrients
between the coral host and the endosymbiotic algae (zooxanthellae) is more challenging.
Here, we performed a long-term and continuous 15N-labelling experiment to quantify the
proportionate contribution of seawater (external N source) and the animal host
(internal N source) to the total N influx in the endosymbiotic algae. Branches from
the scleractinian corals Porites cylindrica and Montipora digitata from Okinawa,
Japan, were cultured for 2 months in indoor, flow-through, filtered seawater tanks
with the continuous supply of 15N-labelled nitrate. At the initial and after 2, 4,
and 9 weeks of the study, coral branches were collected and the algal and animal
fractions were separated for isotopic analyses. In both corals, the N isotope ratio of
symbiotic algae exponentially increased and the values were much higher than those
of the host tissue, suggesting that the algae had a faster turnover N time than the
animal host. Algal and host N biomass normalized to the coral surface area slowly
decreased in both coral species over the study period. To calculate the contribution of
internal and external N, a simple mixing model of algal N metabolism was designed.
Using differential equations of 15N balance and N biomass balance, F1 and F2
(external and internal N fluxes to symbiotic algae, respectively) were expressed as the
functions of time. The model calculations showed that F2 was much higher than F1
in P. cylindrica and the percentage of internal N to the total influx N (PIN) was
>70%. On the other hand, the contribution of F1 and F2 was comparable in M.
digitata and the PIN was 40–70%. These results quantitatively showed that the
internal N pool in the coral tissue plays an important role in the symbiotic algal
metabolism. The application of the present 15N-tracer technique would enable us to
further calculate the fluxes of internal and external N in not only corals but also
other algal-animal symbiotic organisms under various environmental conditions. |
|
|
|
|
|
|