Euphausiid respiration model revamped, link to model results

Euphausiids constitute major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Changes in the abiotic conditions also shape Euphausiid metabolism including aerobic and anaerobic energy production. Here we introduce a global krill respiration model which includes the effect of latitude (LAT), the day of the year of interest (DoY), and the number of daylight hours on the day of interest (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth) in the ANN model (Artificial Neural Networks). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r**2=0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. We also tested for seasonality the standard respiration rate of the most common species that were investigated until now in a large range of DLh and DoY with Multiple Linear Regression (MLR) or General Additive model (GAM). GAM successfully integrated DLh (r**2= 0.563) and DoY (r**2= 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. Neither the MLR nor the GAM approach worked for the North Pacific krill Euphausia pacifica, and MLR for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modelling.

磷虾类（Euphausiids）是陆架生态系统中的主要生物量组分，其昼夜垂直迁移（DVM）过程在碳从海洋表层向深层的快速垂直运输中发挥着关键作用。DVM的深度与迁移模式取决于海洋环境条件，具体涉及温度、光照及深层水域的氧气可利用性——这些因素在多数海洋区域中高度依赖季节变化。非生物条件的改变还会塑造磷虾类的代谢过程，包括有氧与无氧能量产生。

本文介绍一种全球磷虾呼吸模型，除人工神经网络（ANN）模型中决定变温动物耗氧量的基础变量（温度、体重及深度）外，该模型还纳入了纬度（LAT）、目标日期在年内的天数（DoY）及目标日期的日照时长（DLh）的影响。新加入的参数将季节与光周期维度下的时空因素与磷虾呼吸关联起来。当纳入DLh与LAT时，ANN模型的拟合度更优（r²=0.780），表明呼吸作用随纬度升高及日照时长减少而减弱。因此，我们建议在构建南北半球的生理模型时，将DLh作为潜在变量纳入考量。

我们还利用多元线性回归（MLR）与广义相加模型（GAM），针对目前已研究的常见物种的标准呼吸速率开展了季节性测试。广义相加模型成功整合了DLh（r²=0.563）与DoY（r²=0.572）对南极磷虾（Euphausia superba）呼吸速率的影响，其代谢活性在6月中旬达到最低，12月底达到最高。多元线性回归与广义相加模型对北太平洋磷虾（Euphausia pacifica）均不适用；针对北大西洋磷虾（Meganyctiphanes norvegica）的多元线性回归分析因季节性数据覆盖不足，结果仍不明确。

我们强烈建议对全球磷虾类关键物种在不同季节开展比较呼吸测量，以提升生态系统建模的准确性。