Predicted distribution of the glass sponge Vazella pourtalesi on the Scotian Shelf and its persistence in the face of climatic variability

Emerald Basin on the Scotian Shelf off Nova Scotia, Canada, is home to a globally unique aggregation of the glass sponge Vazella pourtalesi, first documented in the region in 1889. In 2009, Fisheries and Oceans Canada (DFO) implemented two Sponge Conservation Areas to protect these sponge grounds from bottom fishing activities. Together, the two conservation areas encompass 259 km2. In order to ascertain the degree to which the sponge grounds remain unprotected, we modelled the presence probability and predicted range distribution of V. pourtalesi on the Scotian Shelf using random forest modelling on presence-absence records. With a high degree of accuracy the random forest model predicted the highest probability of occurrence of V. pourtalesi in the inner basins on the central Scotian Shelf, with lower probabilities at the shelf break and in the Fundian and Northeast Channels. Bottom temperature was the most important determinant of its distribution in the model. Although the two DFO Sponge Conservation Areas protect some of the more significant concentrations of V. pourtalesi, much of its predicted distribution remains unprotected (over 99%). Examination of the hydrographic conditions in Emerald Basin revealed that the V. pourtalesi sponge grounds are associated with a warmer and more saline water mass compared to the surrounding shelf. Reconstruction of historical bottom temperature and salinity in Emerald Basin revealed strong multi-decadal variability, with average bottom temperatures varying by 8˚C. We show that this species has persisted in the face of this climatic variability, possibly indicating how it will respond to future climate change.坐落于加拿大新斯科舍省外斯科舍陆架（Scotian Shelf）的翡翠盆地（Emerald Basin），栖息着全球独有的玻璃海绵物种波特莱斯海绵（Vazella pourtalesi），该物种于1889年首次在该区域被记录。2009年，加拿大渔业与海洋部（Fisheries and Oceans Canada, DFO）设立两处海绵保护区，以保护这些海绵礁免受底拖网捕捞活动的侵扰，两处保护区总面积达259平方千米。为明确该海绵礁的未受保护程度，研究团队基于出现-缺失记录，利用随机森林（random forest）模型对斯科舍陆架上的波特莱斯海绵的存在概率与潜在分布范围进行预测。该模型具备较高预测精度，结果显示波特莱斯海绵的最高出现概率集中于斯科舍陆架中部的内盆地区域，而陆架坡折带、芬迪水道（Fundian Channel）及东北水道（Northeast Channels）的出现概率相对较低。模型分析显示，底层水温是调控该物种分布的最关键环境因子。尽管两处海绵保护区覆盖了部分较为集中的波特莱斯海绵种群，但该物种的绝大多数潜在分布区域仍未得到保护，占比超99%。对翡翠盆地水文条件的分析显示，波特莱斯海绵礁所处的水团相比周边陆架水域，水温更高、盐度更大。对翡翠盆地历史底层水温与盐度的重建结果表明，该区域存在显著的多年代际气候变率，底层平均水温波动幅度可达8℃。研究证实，该物种在这种气候变率下仍能持续存续，这或可为预测其对未来气候变化的响应提供参考。