Habitat and fishing control grazing potential on coral reefs,Functional Ecology

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Habitat and fishing control grazing potential on coral reefs
Functional Ecology ( IF 4.6 ) Pub Date : 2019-10-06 , DOI: 10.1111/1365-2435.13457
James P. W. Robinson ₁ , Jamie M. McDevitt‐Irwin ₂ , Jan‐Claas Dajka ₁ , Jeneen Hadj‐Hammou ₁ , Samantha Howlett ₁ , Alexia Graba‐Landry ₃ , Andrew S. Hoey ₃ , Kirsty L. Nash _{4,

5} , Shaun K. Wilson _{6,

7} , Nicholas A. J. Graham ₁

Affiliation

Herbivory is a key process on coral reefs, which, through grazing of algae, can help sustain coral-dominated states on frequently disturbed reefs and reverse macroalgal regime shifts on degraded ones. Our understanding of herbivory on reefs is largely founded on feeding observations at small spatial scales, yet the biomass and structure of herbivore populations is more closely linked to processes which can be highly variable across large areas, such as benthic habitat turnover and fishing pressure. Though our understanding of spatiotemporal variation in grazer biomass is well developed, equivalent macroscale approaches to understanding bottom-up and top-down controls on herbivory are lacking. Here, we integrate underwater survey data of fish abundances from four Indo-Pacific island regions with herbivore feeding observations to estimate grazing rates for two herbivore functions, cropping (which controls turf algae) and scraping (which promotes coral settlement by clearing benthic substrate), for 72 coral reefs. By including a range of reef states, from coral to algal dominance and heavily fished to remote wilderness areas, we evaluate the influences of benthic habitat and fishing on the grazing rates of fish assemblages. Cropping rates were primarily influenced by benthic condition, with cropping maximized on structurally complex reefs with high substratum availability and low macroalgal cover. Fishing was the primary driver of scraping function, with scraping rates depleted at most reefs relative to remote, unfished reefs, though scraping did increase with substratum availability and structural complexity. Ultimately, benthic and fishing conditions influenced herbivore functioning through their effect on grazer biomass, which was tightly correlated to grazing rates. For a given level of biomass, we show that grazing rates are higher on reefs dominated by small-bodied fishes, suggesting that grazing pressure is greatest when grazer size structure is truncated. Stressors which cause coral declines and clear substrate for turf algae will likely stimulate increases in cropping rates, in both fished and protected areas. In contrast, scraping functions are already impaired at reefs inhabited by people, particularly where structural complexity has collapsed, indicating that restoration of these key processes will require scraper biomass to be rebuilt towards wilderness levels.

中文翻译：

珊瑚礁栖息地和渔业控制放牧潜力

食草是珊瑚礁的一个关键过程，通过藻类的放牧，可以帮助在经常受到干扰的珊瑚礁上维持珊瑚主导的状态，并逆转退化珊瑚礁上的大型藻类政权转变。我们对珊瑚礁食草动物的理解主要建立在小空间尺度的摄食观察上，但食草动物种群的生物量和结构与大区域内高度可变的过程更密切相关，例如底栖栖息地周转和捕捞压力。尽管我们对食草动物生物量的时空变化的理解已经很成熟，但缺乏理解自下而上和自上而下对食草动物的控制的等效宏观方法。这里，我们将来自四个印度太平洋岛屿地区的鱼类丰度水下调查数据与食草动物摄食观察相结合，以估计两种食草动物功能的放牧率，即种植（控制草皮藻类）和刮削（通过清除底栖基质促进珊瑚沉降），72珊瑚礁。通过包括从珊瑚到藻类优势以及大量捕捞到偏远荒野地区的一系列珊瑚礁状态，我们评估了底栖栖息地和捕鱼对鱼类群落放牧率的影响。种植率主要受底栖条件的影响，在结构复杂、基质利用率高、大型藻类覆盖率低的珊瑚礁上种植最大化。捕鱼是刮削功能的主要驱动力，相对于偏远未捕捞的珊瑚礁，大多数珊瑚礁的刮削率已耗尽，尽管刮削确实随着基质可用性和结构复杂性而增加。最终，底栖和捕鱼条件通过对食草动物生物量的影响来影响食草动物的功能，而食草动物生物量与放牧率密切相关。对于给定的生物量水平，我们表明在以小型鱼类为主的珊瑚礁上的放牧率较高，这表明当食草动物的大小结构被截断时，放牧压力最大。导致珊瑚减少和草皮藻类清除基质的压力因素可能会刺激捕鱼区和保护区的种植率增加。相比之下，人类居住的珊瑚礁的刮擦功能已经受损，特别是在结构复杂性已经崩溃的地方，

更新日期：2019-10-06

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