Duncan Murray I, James Nicola C, Potts Warren M, Bates Amanda E
Department of Ichthyology and Fisheries Science, Rhodes University, Prince Alfred street, Makhanda, 6140, South Africa.
South African Institute for Aquatic Biodiversity, 11 Somerset street, Makhanda, 6139, South Africa.
Conserv Physiol. 2020 Oct 26;8(1):coaa090. doi: 10.1093/conphys/coaa090. eCollection 2020.
The distributions of ectothermic marine organisms are limited to temperature ranges and oxygen conditions that support aerobic respiration, quantified within the metabolic index (ϕ) as the ratio of oxygen supply to metabolic oxygen demand. However, the utility of ϕ at local scales and across heterogenous environments is unknown; yet, these scales are often where actionable management decisions are made. Here, we test if ϕ can delimit the entire distribution of marine organisms when calibrated across an appropriate temperature range and at local scales (~10 km) using the endemic reef fish, , which is found in the highly heterogenous temperature and oxygen environment along the South African coastal zone, as a model species. In laboratory experiments, we find a bidirectional (at 12°C) hypoxia tolerance response across the temperature range tested (8 to 24°C), permitting a piecewise calibration of ϕ. We then project this calibrated ϕ model through temperature and oxygen data from a high spatial resolution (11 to 13 km) ocean model for the periods 2005 to 2009 and 2095 to 2099 to quantify various magnitudes of ϕ across space and time paired with complementary occurrence points. Using random forest species distribution models, we quantify a critical ϕ value of 2.78 below which cannot persist and predict current and future distributions of in line with already observed distribution shifts of other South African marine species. Overall, we find that ' distribution is limited by increasing temperatures towards its warm edge but by low oxygen availability towards its cool edge, which is captured within ϕ at fine scales and across heterogenous oxygen and temperature combinations. Our results support the application of ϕ for generating local- and regional-scale predictions of climate change effects on organisms that can inform local conservation management decisions.
变温海洋生物的分布局限于支持有氧呼吸的温度范围和氧气条件，在代谢指数（ϕ）中，其被量化为氧气供应与代谢需氧量的比值。然而，ϕ在局部尺度和异质环境中的效用尚不清楚；然而，这些尺度往往是做出可操作管理决策的地方。在这里，我们以在南非沿海地区高度异质的温度和氧气环境中发现的特有礁鱼 作为模型物种，测试当在适当的温度范围和局部尺度（约10公里）进行校准时，ϕ是否能够界定海洋生物的整个分布范围。在实验室实验中，我们发现在测试的温度范围（8至24°C）内存在双向（在12°C时）缺氧耐受反应，从而允许对ϕ进行分段校准。然后，我们通过2005年至2009年以及2095年至2099年期间高空间分辨率（11至13公里）海洋模型的温度和氧气数据，对这个校准后的ϕ模型进行投影，以量化不同时空尺度下与互补出现点配对的各种ϕ值。使用随机森林物种分布模型，我们量化了一个关键的ϕ值2.78，低于这个值 无法生存，并预测了 的当前和未来分布，这与已经观察到的其他南非海洋物种的分布变化一致。总体而言，我们发现 的分布在向暖边缘方向受到温度升高的限制，但在向冷边缘方向受到低氧可用性的限制，这在精细尺度以及异质的氧气和温度组合下被ϕ所捕获。我们的结果支持应用ϕ来生成关于气候变化对生物影响的局部和区域尺度预测，从而为地方保护管理决策提供信息。
