Setting thresholds for good status in marine ecosystem management

环境管理的目的是实现理想的生态系统状态，避免不利或退化的状态。评估生态系统状态需要条件和阈值的定量指标，高于阈值的状态被定义为“良好”（Rice等人，2012; Levin等人，2016）。例如，对于根据《海洋生物指令》指定的海洋保护区，养护状况考虑到种群数量、物种的自然分布范围以及生境的结构和功能等参数。要满足对海洋保护区的生态期望，就必须避免渔业和其他人类活动的不利影响，并确定生态系统状态的阈值，低于该阈值，系统就会退化，也不再产生任何社会经济效益。确定好或有利状态与坏或差状态之间的阈值在哪里已经使用了各种各样的方法，并且是偶然和主观的（Dorrough等人，2020年）。例如，现有的方法从确定生态系统状态-压力关系中的统计学推导的断点到专家启发（Dorrough等人，2020; Hillebrand等人，2020年）。此外，一些阈值旨在维持国家本身，而另一些阈值旨在维持国家支持的生态系统功能或生物多样性。不同的方法可能会导致促使管理行动的门槛非常不同，这些也可能对依赖社区产生非常不同的社会影响和后果。因此，迫切需要确定所确定的理想生态系统状态的不同阈值的各种利弊。例如，联合自然保护委员会（JNCC）在管理联合王国海洋保护区的底拖网渔业时需要这些阈值;国际海洋考察理事会（ICES）需要这些阈值，以便就如何执行海洋战略框架指令向欧盟提供咨询意见（MFSD，ICES，2021）; OSPAR和英国政府评估生物多样性状况，以执行MSFD（OSPAR）和英国海洋战略（UKMS）;以及通过《人居条例》评估的计划和项目，以确定是否存在不利影响，如果存在，则采取何种补偿措施最能支持这一地位。目前对NetGain的兴趣日益增加也是相关的，因为这需要了解目前的保护状况以及可以采取哪些措施来改善这种状况。事实上，如果没有阈值，就不可能确定生物多样性指标是否处于《海洋可持续发展框架》/《联合王国海洋管理体系》规定的良好环境状态;目前的远洋生境、底栖生境和食物网指标就是这种情况，由于缺乏阈值，无法评估这些指标的环境状态。因此，从政策角度来看，必须商定阈值，以便能够对生物多样性进行有力的评估，并采取适当的管理行动。

Environmental management aims to achieve desirable ecosystem states and avoid adverse or degraded states. Assessing ecosystem state requires quantitative indicators of condition and thresholds above which state is defined as 'good' (Rice et al., 2012; Levin et al., 2016). For example, for MPAs designated under the Habitats Directive, conservation status takes account of parameters such as the population abundance, the natural range of a species and the structure and function of a habitat. Meeting the ecological expectations placed on MPAs requires avoiding adverse impacts from fisheries and other human activities and identifying thresholds in ecosystem state below which the system becomes degraded and also no longer confers any socio-economic benefits. Identifying where this threshold between good or favourable status and bad or poor status lies has used a wide variety of approaches and has been haphazard and subjective (Dorrough et al., 2020). For example, existing approaches range from identifying statistically derived breakpoints in the ecosystem state-pressure relationships to expert-elicitation (Dorrough et al., 2020; Hillebrand et al., 2020). Furthermore, some thresholds aim to maintain the state itself, while others aim to maintain the ecosystem functions or biodiversity that are supported by the state. Different approaches may result in very different thresholds for prompting management actions, and these may also have very different social impacts and consequences on dependent communities. There is therefore an urgent need to identify the various pros and cons of the different thresholds for desirable ecosystem states identified. Such thresholds are, for example, needed by the Joint Nature Conservation Committee (JNCC) in the management of bottom trawl fisheries in MPAs in the UK; by the International Council for the Exploration of the Sea (ICES) for advice to the EU on how to implement the Marine Strategy Framework Directive (MFSD, ICES, 2021); by OSPAR and the UK government for assessing the state of biodiversity for implementation of the MSFD (OSPAR) and UK Marine Strategy (UKMS); and for plans and projects assessed through the Habitat Regulations to determine if adverse effect applies and, if it does, what compensation measures could best support the status. Current and increasing interest in NetGain is also relevant, as that requires an understanding of current conservation status and what measures could be taken to improve that. Indeed, it is not possible to determine if biodiversity indicators are in Good Environmental Status under the MSFD/UKMS without thresholds; this is currently the case for pelagic habitats, benthic habitats, and food web indicators, which are unable to be assessed for environmental status because of the lack of thresholds. From a policy perspective, therefore, it is imperative that thresholds are agreed so biodiversity can be robustly assessed, and appropriate management actions implemented.