Australian Institute of Marine Science, Townsville, Queensland, Australia.
PLoS One. 2013;8(1):e54399. doi: 10.1371/journal.pone.0054399. Epub 2013 Jan 17.
Global warming, and nutrient and sediment runoff from coastal development, both exert increasing pressures on coastal coral reefs. The objective of this study was to resolve the question of whether coastal eutrophication may protect corals from thermal stress by improving their nutritional status, or rather diminish their thermal tolerance through the synergy of dual stressors. A review of previous studies on the topic of combined trophic status and heat exposure on the thermal tolerance of corals reveals a broad range of outcomes, including synergistic, additive and antagonistic effects. We conducted a 90-day long experiment exposing corals to realistic levels of elevated nutrients and sediments, and heat stress. Colonies of two common scleractinian corals (Acropora millepora and Montipora tuberculosa) were kept in coastal seawater, or coastal seawater that was further organically and nutrient enriched (OE), and/or enriched with nitrate. Batches of OE were created daily, facilitating nutrient uptake, plankton succession and organic enrichment as observed in coastal waters. After 10 days of acclimation, 67% of the colonies had their temperature gradually increased from 27° to 31.2°C. After 3-7 weeks of heat stress, colonies of both species had significantly greater reductions in fluorescence yields and lower survival in OE than without addition of OE. Furthermore, photophysiological recovery was incomplete 31-38 days after ending the heat stress only in the OE treatments. Nitrate alone had no measurable effect on survival, bleaching and recovery in either species. Skeletal growth rates were reduced by 45% in heat-stressed A. millepora and by 24% in OE-exposed M. tuberculosa. We propose a conceptual trophic framework that resolves some of the apparently contradictory outcomes revealed by the review. Our study shows that management actions to reduce coastal eutrophication can improve the resistance and resilience of vulnerable coastal coral reefs to warming temperatures.
全球变暖以及沿海开发导致的营养物质和沉积物径流，都对沿海珊瑚礁施加了越来越大的压力。本研究的目的是要解决这样一个问题，即沿海富营养化是否可以通过改善珊瑚的营养状况来保护珊瑚免受热应激，还是通过双重胁迫的协同作用降低其热耐受性。对之前关于富营养化状态和热暴露对珊瑚热耐受性的综合研究进行综述后发现，结果存在广泛的差异，包括协同、相加和拮抗作用。我们进行了为期 90 天的实验，将珊瑚暴露在升高的营养物质和沉积物以及热胁迫的现实水平下。两种常见的珊瑚（鹿角珊瑚和丛生盔形珊瑚）的群体被放置在沿海水域，或进一步用有机物质和营养物质富化（OE）的沿海水域，或用硝酸盐富化的沿海水域。每天都要创建 OE 批次，以促进营养物质的吸收、浮游生物的演替和沿海水域中观察到的有机富化。适应期 10 天后，有 67%的群体其温度逐渐从 27°C升高到 31.2°C。在热胁迫 3-7 周后，与不添加 OE 相比，两种珊瑚的群体在 OE 处理中荧光产量显著降低，存活率显著降低。此外，仅在 OE 处理中，在结束热胁迫后 31-38 天，光生理恢复仍不完全。硝酸盐单独对两种珊瑚的存活率、白化和恢复均无明显影响。热胁迫下的鹿角珊瑚的骨骼生长速率降低了 45%，OE 暴露下的丛生盔形珊瑚的骨骼生长速率降低了 24%。我们提出了一个概念性的营养框架，解决了综述中揭示的一些看似矛盾的结果。我们的研究表明，减少沿海富营养化的管理措施可以提高脆弱的沿海珊瑚礁对变暖温度的抵抗力和恢复力。
