DOC concentrations across a depth-dependent light gradient on a Caribbean coral reef
DOC concentrations across a depth-dependent light gradient on a Caribbean coral reef
复制标题
加勒比珊瑚礁上随深度变化的光梯度 DOC 浓度
作者：
B. Mueller;E. Meesters;Fleur C. van Duyl
底栖初级生产者（BPP），如礁藻和石珊瑚释放的光合产物，燃料溶解有机碳（DOC）的生产在热带珊瑚礁。与周围水柱相比，BPP附近的DOC浓度一再被观察到升高。由于BPP的DOC释放随着光照的增加而增加，因此附近DOC浓度的升高也部分取决于光照的可用性。因此，DOC浓度很可能是较高的浅，光线充足的礁阶比在较深的部分前礁坡。我们测量就地DOC浓度和光强度在靠近珊瑚礁Dictyota SP。和石珊瑚Orbicella faveolata沿沿着深度依赖的光梯度从5至20米的深度，并比较这些在水柱中的背景浓度。在10米（中等光照）处，与水柱中的背景浓度相比，网藻附近的DOC浓度升高了15 µmol C L−1，但在5米和20米（分别为高光和低光）或O附近则没有。在任何测试深度的faveolata。DOC浓度没有不同的深度，从而为任何测试的水类型的光环境。然而，水的类型和深度似乎共同影响原位DOC浓度在整个测试的深度依赖性光梯度。对光系统II激发压力的确证性非原位测量表明，在Dictyota sp.中的光抑制很可能发生在光强度下，这种光强度通常存在于库拉索岛珊瑚礁上，中午在5米深处的高光水平下。因此，光抑制可能减少了DOC的释放网藻和DOC浓度在其附近。我们的研究结果表明，DOC浓度升高的发生并不遵循跨深度的自然光梯度。相反，多个因素的组合，如水的类型，光的可用性（包括光抑制的限制），和水的运动提出了交互式确定DOC浓度在BPP附近。
Photosynthates released by benthic primary producers (BPP), such as reef algae and scleractinian corals, fuel the dissolved organic carbon (DOC) production on tropical coral reefs. DOC concentrations near BPP have repeatedly been observed to be elevated compared to those in the surrounding water column. As the DOC release of BPP increases with increasing light availability, elevated DOC concentrations near them will, in part, also depend on light availability. Consequently, DOC concentrations are likely to be higher on the shallow, well-lit reef terrace than in deeper sections on the fore reef slope. We measured in situ DOC concentrations and light intensity in close proximity to the reef alga Dictyota sp. and the scleractinian coral Orbicella faveolata along a depth-dependent light gradient from 5 to 20 m depth and compared these to background concentrations in the water column. At 10 m (intermediate light), DOC concentrations near Dictyota sp. were elevated by 15 µmol C L−1 compared to background concentrations in the water column, but not at 5 and 20 m (high and low light, respectively), or near O. faveolata at any of the tested depths. DOC concentrations did not differ between depths and thereby light environments for any of the tested water types. However, water type and depth appear to jointly affect in situ DOC concentrations across the tested depth-dependent light gradient. Corroborative ex situ measurements of excitation pressure on photosystem II suggest that photoinhibition in Dictyota sp. is likely to occur at light intensities that are commonly present on Curaçaoan coral reefs under high light levels at 5 m depth during midday. Photoinhibition may have thereby reduced the DOC release of Dictyota sp. and DOC concentrations in its close proximity. Our results indicate that the occurrence of elevated DOC concentrations did not follow a natural light gradient across depth. Instead, a combination of multiple factors, such as water type, light availability (including the restriction by photoinhibition), and water movement are proposed to interactively determine the DOC concentrations in the close vicinity of BPP.