ARC Centre of Excellence for Coral Reef Studies and College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia.
ARC Centre of Excellence for Coral Reef Studies and College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia.
Sci Total Environ. 2020 Apr 15;713:136709. doi: 10.1016/j.scitotenv.2020.136709. Epub 2020 Jan 15.
Coral reefs are highly productive ecosystems, with much of this productivity arising from the algal turfs which cover the hard reef substratum. This productivity can flow up the food chain through herbivorous fishes, to be harvested by humans as fishable biomass. However, algal turfs exist on a spectrum of forms from short productive algal turfs (SPATs), to long sediment-laden algal turfs (LSATs). The latter are increasingly likely to typify Anthropocene coral reefs, however, we have a limited understanding of their nature and potential productivity. We assessed the nature of algal turfs in terms of length, biomass, relative detritus content, and productivity across a sediment load gradient, from SPATs to LSATs, at two reefs separated by >450 km along Australia's Great Barrier Reef (GBR). Furthermore, to assess the capacity of sediments to shape productivity, we modelled algal turf productivity, as a function of sediment load, across multiple spatial scales in a Bayesian framework. We recorded precipitous declines in both the productivity of algal turfs, and the relative nutritional value of particulates, up to sediment loads of ~100 g m. However, algal turf biomass did not change with sediment loads. This appears to reflect a shift in algal community composition from short, high-biomass, highly-productive algae at low sediment loads, to longer, low-biomass, less productive algae at high sediment loads. Importantly, these relationships provide a robust framework for estimating algal turf productivity on coral reefs. Indeed, when we applied our models to known sediment loads, we reveal that sediment loads alone can explain observed algal turf productivity gradients across multiple spatial scales. In an era of global climate change and coral reef reconfiguration, algal turf sediments may hold the key to maintaining benthic productivity on coral reefs in the Anthropocene.
珊瑚礁是高生产力的生态系统，其中大部分生产力来自覆盖硬珊瑚基质的藻类草皮。这种生产力可以通过草食性鱼类沿着食物链向上流动，然后被人类作为可捕捞的生物量收获。然而，藻类草皮存在于一个从短而高生产力的藻类草皮（SPATs）到长而富含沉积物的藻类草皮（LSATs）的连续谱中。后者越来越可能成为人类世珊瑚礁的典型特征，但我们对它们的性质和潜在生产力的了解有限。我们根据长度、生物量、相对碎屑含量和生产力评估了藻类草皮的性质，在澳大利亚大堡礁（GBR）相隔超过 450 公里的两个珊瑚礁上，从 SPATs 到 LSATs，跨越了一个沉积物负荷梯度。此外，为了评估沉积物塑造生产力的能力，我们在贝叶斯框架中，以模型的方式，根据沉积物负荷评估了藻类草皮生产力在多个空间尺度上的变化。我们记录到藻类草皮的生产力和颗粒体的相对营养价值都急剧下降，直到沉积物负荷约为 100 克/平方米。然而，藻类草皮生物量并没有随沉积物负荷的变化而变化。这似乎反映了藻类群落组成的变化，从低沉积物负荷下短而高生物量、高生产力的藻类，转变为高沉积物负荷下长而低生物量、低生产力的藻类。重要的是，这些关系为估计珊瑚礁上藻类草皮的生产力提供了一个稳健的框架。事实上，当我们将我们的模型应用于已知的沉积物负荷时，我们揭示了沉积物负荷本身可以解释在多个空间尺度上观察到的藻类草皮生产力梯度。在全球气候变化和珊瑚礁重构的时代，藻类草皮沉积物可能是维持人类世珊瑚礁底栖生产力的关键。
