Factors limiting marine connectivity at a species' range edge - the case of the pink sea fan, Eunicella verrucosa

粉红色的海扇，被称为疣状珠螺，被列入世界自然保护联盟的红色名录，是英国水域的受保护物种。它被列为受保护的特征，这是2013年和2016年英格兰西南部指定的许多mcz的关键因素。了解该物种的多样性和连通性对于物种保护和进一步候选mcz的指定至关重要（Natural England, 2016）。我们预计这项研究将为这两个关键因素提供信息。拟议中的项目将调查基因流动的海洋路径和障碍的程度，例如，由于潮汐混合锋和海岸/河口环流模式等残余洋流，以及选择在推动英国西南部粉红色海扇种群之间遗传差异中的作用。疣状棘球蚴是一种播撒产卵者，其幼虫依靠洋流传播，然而，迄今为止，人们对这种物种的基本生物学知之甚少，对其在水层中的停留时间或其应对热应力的能力知之甚少。因此，我们将进行建模和水族馆研究，开始探索可能导致这些范围边缘种群缺乏招募的关键生物学因素。较明显的研究途径包括：热应激、影响产卵时间的因素、产卵持续时间、水体存活和中上层幼虫持续时间。当这些数据变得可用时，它们随后可以被参数化到我们的海洋学模型中。高质量的物理（电流、温度）和生物（如种群分布、幼虫行为）数据将用于模型的基础真实性，并将设计一个敏感性框架，以在基于自然变异性和模型参数化的不确定性范围内设置扩散/连接结果。我们在埃克塞特保存了大量的海扇组织样本，这些样本是从东北大西洋和地中海西部的物种范围内收集的，对这个提议至关重要的是，我们现在已经获得了与威尔士彭布罗克郡斯科默海洋保护区的NRW工作人员合作的许可，从最近定居在斯科默海洋保护区的新招募人员身上采集组织样本。一个关键的目标将是确定斯科默新海扇的低水平招募是否是由于连性，选择（可能是温度，特别是冬季最低温度），或者是否（或在多大程度上）Allee效应正在起作用，即成熟成年扇的人口密度现在如此之低（很少扇，广泛间隔），配子找到彼此的机会降低到一个未知的临界阈值以下。斯科默的发现将与伦迪的发现进行比较，伦迪是一个纬度相似的地点，但与康沃尔北部和西部以及锡利群岛的粉海扇主要种群有更强大的水下联系。我们将使用一种称为RAD-seq的分子技术来鉴定与特定地理区域和/或特定选择压力相关的单核苷酸多态性（snp）位点。我们正在进行的项目（埃克塞特）最近完成了对粉红海扇基因组中数千个snp的筛选-将根据其区分感兴趣群体的能力（基于FST）选择最具歧视性的snp小组。总而言之，该项目为研究生提供了独特的跨学科研究培训，有机会获得分子遗传学，海洋学建模和敏感海洋生物的水族馆操作方面的经验，产生的结果将通过我们的CASE合作伙伴，自然英格兰和我们的合作伙伴，自然资源威尔士直接为英国的海洋政策提供信息。这样的组合应该提供高技能和就业的年轻研究人员。

The pink sea fan, Eunicella verrucosa, is IUCN red-listed and is a protected species in UK waters. It is listed as a Protected Feature, a key factor in the designation of many of the MCZs designated in southwest England in 2013 and 2016. An understanding of the diversity and connectivity of this species is essential for both conservation of the species and the designation of further candidate MCZs (Natural England, 2016). We anticipate that this research will inform on both these key factors. The proposed project will investigate the extent of oceanographic pathways and barriers to gene flow, e.g. due to residual currents such as tidal mixing fronts and coastal/estuarine circulation patterns, and the role of selection in driving genetic differences between populations of pink sea fan at the northern limit of its range in southwest Britain. E. verrucosa is a broadcast spawner, with larvae reliant on oceanic currents for dispersal, and yet, to date, very little is known about the basic biology of this species, with little or no knowledge of its retention time in the water column or its ability to deal with thermal stress. Accordingly, we will undertake modelling and aquarium studies to begin to explore key biological factors that might be contributing to the lack of recruitment into these range edge populations. Obvious avenues for investigation include: heat stress, factors affecting spawning time, spawning duration, survival in the water column and pelagic larval duration. As these data become available these can subsequently be parameterised into our oceanographic models. High quality physical (currents, temperatures) and biological (e.g. population distributions, larval behaviour) data will be used to ground-truth the models, and a sensitivity framework will be designed to set the dispersal/connectivity results within uncertainties based on natural variability and model parameterisations. We hold at Exeter an extensive selection of sea fan tissue samples collected from across the species' range in the northeast Atlantic and the western Mediterranean and, critical to this proposal, we have now obtained permission to work with NRW staff at the Skomer Marine Reserve in Pembrokeshire, Wales, to take tissue samples from new recruits which have recently settled within the Skomer Marine Reserve. A key objective will be to establish whether the low level of recruitment of new sea fans at Skomer is due to connectivity, selection (possibly temperature, esp., minimum winter temperature), or whether (or to what extent) the Allee effect is acting, whereby the population density of mature adult fans is now so low (few fans, widely spaced) that the chances of gametes finding each other are reduced below an as yet unknown critical threshold. Findings for Skomer will be compared with those obtained at Lundy, a site at a similar latitude, but with potentially more robust in-water connectivity to major populations of pink sea fan in north and west Cornwall and the Isles of Scilly. We will use a molecular technique known as RAD-seq to identify single nucleotide polymorphism (SNPs) loci associated with particular geographical regions and/or with particular selection pressures. Our on-going project (Exeter) has recently finalised the screening of several thousand SNPs from across the pink sea fan genome - a panel of the most discriminating SNPs will be selected based on their ability to discriminate populations of interest (based on FST). In summary, the project offers a unique, trans-disciplinary research training for a postgraduate student with opportunities to gain experience in molecular genetics, oceanographic modelling and aquarium manipulations of sensitive marine organisims, generating results that will feed directly into UK marine policy through our CASE partner, Natural England, and our associate partner, Natural Resources Wales. Such a mix should deliver a highly skilled and employable young researcher.