Nutrient-induced perturbations to δ13C and δ15N in symbiotic dinoflagellates and their coral hosts

Abstract

Inorganic nutrients play a critical role in determining benthic community structure in tropical seas. This study examined the impact of adding inorganic nutrients (ammonium and phosphate) on the isotopic composition of 2 reef-building corals, Pocillopora damicornis and Heliofungia actiniformis, on the southern Great Barrier Reef. The addition of elevated nutrients to patch reefs that pond at low tide did not perturb the C:N ratio of either species or their symbiotic dinoflagellates. The C:N ratios were significantly higher in material extracted from the skeleton (14.8 ± 1.50 and 10.8 ± 1.42) than either host (7.6 ± 0.87 and 6.0 ± 0.71) or symbiotic dinoflagellates (5.7 ± 0.48 and 6.9 ± 0.66) (P. damicornis and H. actiniformis respectively; ± 95 confidence intervals). The ratio of acquired N to background N suggests that the added dissolved inorganic nitrogen (DIN) accounted for 50 to 100% of total nitrogen within the tissues of P. damicornis and H. actiniformis at the end of the experiment. The addition of the isotopically depleted nutrients (δ 15 N = 0 ‰) to patch reefs significantly decreased δ 15 N from control values of between 3 and 4 to values to below 1 in the case of all compartments, while δ 13 C values were relatively unresponsive to nutrient treatments. These findings suggest that coral δ

A hypothesis linking sub-optimal seawater <I>p</I>CO<sub>2</sub> conditions for cnidarian-<I>Symbiodinium</I> symbioses with the exceedence of the interglacial threshold (>260 ppmv)

“…Indeed, the projected trends indicate that irrespective of temperature or morphology, a fundamental (preconditioning) trigger for zooxanthellae loss is the exceedence of pCO 2 beyond ∼260 ppmv. Significantly, the tank treatments were carried out under high summer irradiance (700-1000 µmol photon m −2 s −1 ) and with a nutrient-replete lagoonal seawater source (Hoegh-Guldberg et al, 2004). The experimental findings are therefore consistent with the proposed importance of high irradiance and nutrient-replete conditions as conditional components for the observed enhancement of thermal bleaching under elevated pCO 2 conditions.…”

Stable isotopes (δ 13 C and δ 15 N) of organic matrix from coral skeleton

“…Phototrophy may well predominate over heterotrophy in symbiotic corals, because even at the low ambient concentrations associated with coral reefs, ammonium uptake is sufficient to supply the daily demand of a symbiotic coral for new nitrogen (42). The similarity of ␦ 15 N in symbiotic coral compartments might be the result of nutrient recycling, which could bring ammonium assimilation products to some equilibrium ␦ 15 N value in algae and animal tissue, including OM precursors (1,10,11,43). It is interesting to note that in several symbiotic corals from the Great Barrier Reef, OM ␦ 15 N is less enriched in 15 N than algae or animal tissue and averages Ϸ1.3‰ (11).…”

“…Natural abundance of stable isotopes (␦ 13 C and ␦ 18 O) has answered paleobiological and modern questions about the effect of photosymbiosis on sources of carbon and oxygen in coral skeletal calcium carbonate (3,4). Similarly, ␦ 13 C and ␦ 15 N have provided information on how coral algae and animal cells use carbon and nitrogen (5)(6)(7)(8)(9)(10)(11). Here we investigate natural abundance of stable isotopes (␦ 13 C and ␦ 15 N) in another coral skeletal compartment, the skeletal organic matrix (OM).…”

Calcification rate and the stable carbon, oxygen, and nitrogen isotopes in the skeleton, host tissue, and zooxanthellae of bleached and recovering Hawaiian corals

“…Isolated and in hospite zooxanthellae uptake dissolved inorganic nitrogen from solution, including ammonium, nitrate, and/or nitrite ions (Burris, 1983;D'Elia et al, 1983;Wilkerson and Trench, 1986). Zooxanthellae stable nitrogen isotopic composition (d 15 N z ) likely reflects changes in the uptake of dissolved inorganic nitrogen from the seawater (Hoegh-Guldberg et al, 2004).…”