Helmer Luke, Farrell Paul, Hendy Ian, Harding Simon, Robertson Morven, Preston Joanne
Institute of Marine Sciences, University of Portsmouth, Portsmouth, Hampshire, UK.
Blue Marine Foundation, London, UK.
PeerJ. 2019 Feb 28;7:e6431. doi: 10.7717/peerj.6431. eCollection 2019.
The decline of the European oyster across its biogeographic range has been driven largely by over-fishing and anthropogenic habitat destruction, often to the point of functional extinction. However, other negatively interacting factors attributing to this catastrophic decline include disease, invasive species and pollution. In addition, a relatively complex life history characterized by sporadic spawning renders biologically vulnerable to overexploitation. As a viviparous species, successful reproduction in populations is density dependent to a greater degree than broadcast spawning oviparous species such as the Pacific oyster () . Here, we report on the benthic assemblage of and the invasive gastropod across three actively managed South coast harbors in one of the few remaining fisheries in the UK. Long-term data reveals that numbers of sampled within Chichester Harbour have decreased by 96%, in contrast numbers of sampled have increased by 441% over a 19-year period. The recent survey data also recorded extremely low densities of and extremely high densities of , within Portsmouth and Langstone Harbours. The native oyster's failure to recover, despite fishery closures, suggests competitive exclusion by is preventing recovery of , which is thought to be due to a lack of habitat heterogeneity or suitable settlement substrate. Large scale population data reveals that mean shell length and width has decreased significantly across all years and site groups from 2015 to 2017, with a narrowing demographic structure. An absence of juveniles and lack of multiple cohorts in the remaining population suggests that the limited fishing effort exceeds biological output and recruitment is poor. In the Langstone & Chichester 2017 sample 98% of the population is assigned to a single cohort (modal mean 71.20 ± 8.78 mm, maximum length). There is evidence of small scale (<5 km) geographic population structure between connected harbors; the 2015 Portsmouth and Chichester fishery populations exhibited disparity in the most frequent size class with 36% within 81-90 mm and 33.86% within 61-70 mm, respectively, the data also indicates a narrowing demographic over a short period of time. The prevalence of the disease Bonamiosis was monitored and supports this microgeographic population structure. Infection rates of by was 0% in Portsmouth Harbor ( = 48), 4.1% in Langstone ( = 145) and 21.3% in Chichester ( = 48) populations. These data collectively indicate that is on the brink of an ecological collapse within the Solent harbors. Without effective intervention to mitigate the benthic dominance by in the form of biologically relevant fishery policy and the management of suitable recruitment substrate these native oyster populations could be lost.
欧洲牡蛎在其生物地理范围内的数量减少，主要是由于过度捕捞和人为栖息地破坏，常常达到功能性灭绝的程度。然而，导致这种灾难性减少的其他负面相互作用因素包括疾病、入侵物种和污染。此外，其相对复杂的生活史以零星产卵为特征，使其在生物学上易受过度开发的影响。作为胎生物种，与太平洋牡蛎（）等卵生的体外受精物种相比，其种群中的成功繁殖在更大程度上依赖于种群密度。在此，我们报告了英国仅存的少数牡蛎渔业之一中，三个积极管理的南海岸港口的欧洲牡蛎底栖生物群落以及入侵腹足类动物情况。长期数据显示，奇切斯特港内采样的欧洲牡蛎数量减少了96%，相比之下，在19年期间，采样的入侵腹足类动物数量增加了441%。最近的调查数据还记录了朴茨茅斯港和朗斯通港内欧洲牡蛎密度极低，而入侵腹足类动物密度极高。尽管渔业关闭，但本地牡蛎未能恢复，这表明入侵腹足类动物的竞争排斥正在阻止欧洲牡蛎的恢复，这被认为是由于缺乏栖息地异质性或合适的附着基质。大规模种群数据显示，从2015年到2017年，所有年份和地点组的欧洲牡蛎平均壳长和壳宽均显著下降，种群结构变窄。剩余种群中没有幼体且缺乏多个年龄组，这表明有限的捕捞努力超过了生物产出，补充率很低。在2017年朗斯通和奇切斯特的样本中，98%的种群属于单一年龄组（众数平均值为71.20±8.78毫米，最大长度）。有证据表明，相连港口之间存在小规模（<5公里）的地理种群结构；2015年朴茨茅斯和奇切斯特渔业种群在最常见的尺寸类别上存在差异，分别为81 - 90毫米范围内占36%，61 - 70毫米范围内占33.86%，数据还表明在短时间内种群结构变窄。对博纳姆病的患病率进行了监测，支持了这种微观地理种群结构。朴茨茅斯港欧洲牡蛎的感染率为0%（n = 48），朗斯通港为4.1%（n = 145），奇切斯特港种群为21.3%（n = 48）。这些数据共同表明，欧洲牡蛎在索伦特海峡港口正处于生态崩溃的边缘。如果没有以具有生物学相关性的渔业政策和合适附着基质管理的形式进行有效干预，以减轻入侵腹足类动物的底栖优势，这些本地牡蛎种群可能会消失。
