Marine Ecology Department, Faculty of Biology & Chemistry (FB 2), University of Bremen, Bremen, Germany.
School of Science, University of Waikato, Tauranga, New Zealand.
PeerJ. 2023 Feb 17;11:e14812. doi: 10.7717/peerj.14812. eCollection 2023.
Dissolved organic carbon (DOC) enrichment and ocean warming both negatively affect hard corals, but studies on their combined effects on other reef organisms are scarce. Octocorals are likely to become key players in future reef communities, but they are still highly under-investigated with regard to their responses to global and local environmental changes. Thus, we evaluated the individual and combined effects of DOC enrichment (10, 20 and 40 mg L DOC, added as glucose) and warming (stepwise from 26 to 32 °C) on the widespread Indo-Pacific gorgonian in a 45-day laboratory experiment. Oxygen fluxes (net photosynthesis and respiration), as well as Symbiodiniaceae cell density and coral growth were assessed. Our results highlight a differential ecophysiological response to DOC enrichment and warming as well as their combination. Individual DOC addition did not significantly affect oxygen fluxes nor Symbiodiniaceae cell density and growth, while warming significantly decreased photosynthesis rates and Symbiodiniaceae cell density. When DOC enrichment and warming were combined, no effect on oxygen fluxes was observed while growth responded to certain DOC conditions depending on the temperature. Our findings indicate that is insensitive to the individual effect of DOC enrichment, but not to warming and the two stressors combined. This suggests that, if temperature remains below certain thresholds, this gorgonian species may gain a competitive advantage over coral species that are reportedly more affected by DOC eutrophication. However, under the expected increasing temperature scenarios, it is also likely that this octocoral species will be negatively affected, with potential consequences on community structure. This study contributes to our understanding of the conditions that drive phase shift dynamics in coastal coral reef ecosystemds.
溶解有机碳 (DOC) 富集和海洋变暖均会对硬珊瑚产生负面影响，但关于它们对其他珊瑚生物综合影响的研究却很少。八放珊瑚纲动物可能会成为未来珊瑚群落中的主要角色，但由于对其对全球和局部环境变化的反应的研究还很少，因此它们仍然被严重低估了。因此，我们在 45 天的实验室实验中评估了 DOC 富集（10、20 和 40mgL DOC，以葡萄糖形式添加）和升温（逐步从 26°C 升至 32°C）对分布广泛的印度洋-太平洋柳珊瑚的单独和综合影响。评估了氧气通量（净光合作用和呼吸作用）、共生藻细胞密度和珊瑚生长情况。我们的结果强调了对 DOC 富集和升温以及它们的组合的不同生理生态响应。单独添加 DOC 不会显著影响氧气通量或共生藻细胞密度和生长，而升温则显著降低了光合作用速率和共生藻细胞密度。当 DOC 富集和升温相结合时，氧气通量没有受到影响，而生长则根据温度对某些 DOC 条件作出反应。我们的研究结果表明，对单独的 DOC 富集效应不敏感，但对升温和两种胁迫因素的组合不敏感。这表明，如果温度保持在一定阈值以下，这种柳珊瑚物种可能会在竞争中获得优势，超过那些据报道更容易受到 DOC 富营养化影响的珊瑚物种。然而，在预期的升温情景下，这种八放珊瑚纲动物也可能受到负面影响，这可能会对群落结构产生潜在影响。这项研究有助于我们了解驱动沿海珊瑚礁生态系统相变动态的条件。
