Setting thresholds for good status in marine ecosystem management

环境管理的目标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量化指标，超过这些指标的状态被定义为“良好”(莱斯等人，2012年；莱文等人，2016年)。例如，对于根据《生境指令》指定的海洋保护区，保护状况考虑的参数包括种群数量、物种的自然范围以及栖息地的结构和功能。要实现对海洋保护区的生态期望，就需要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，低于这个阈值，系统就会退化，也不再带来任何社会经济利益。确定好的或有利的地位和坏的或不好的地位之间的界限在哪里，使用了各种各样的方法，而且一直是随意和主观的(Dorrouw等人，2020年)。例如，现有方法的范围从确定生态系统状态-压力关系中的统计衍生断点到专家-启发(Dorough等人，2020年；Hillebrand等人，2020年)。此外，一些门槛旨在维持国家本身，而另一些门槛旨在维持国家支持的生态系统功能或生物多样性。不同的方法可能会产生非常不同的促使管理行动的门槛，这些也可能对依赖的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)在管理英国海洋保护区的底层拖网渔业时需要这样的阈值；国际海洋勘探理事会(ICES)就如何执行《海洋战略框架指令》(MFSD，ICES，2021年)向欧盟征求咨询意见；奥斯巴和联合王国政府需要评估生物多样性状况，以执行MSFD(OSPAR)和英国海洋战略(UKMS)；通过《生境条例》进行评估的计划和项目，以确定是否存在不利影响，如果有，什么补偿措施最能支持这一状况。目前对NetGain的兴趣越来越大也是相关的，因为这需要了解目前的保护状况，以及可以采取什么措施来改善这一状况。事实上，在没有阈值的情况下，无法确定生物多样性指标在MSFD/UKMS下是否处于良好的环境状况；目前，中上层生境、底栖生境和食物网指标就是这种情况，由于缺乏阈值，无法评估它们的环境状况。因此，从政策的角度来看，当务之急是商定门槛，以便对生物多样性进行强有力的评估，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.