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.

加拿大新斯科舍省外的斯科舍陆坡（Scotian Shelf）上的翡翠盆地（Emerald Basin），栖息着全球独有的玻璃海绵沃氏偕老同穴（Vazella pourtalesi）种群，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）设立了两处海绵保护区，以保护这些海绵礁免受底拖捕捞活动的破坏。两处保护区的总面积达259平方千米。
为明确该海绵礁的未受保护程度，我们基于存在-缺失观测记录，采用随机森林（random forest）模型对斯科舍陆坡上沃氏偕老同穴的存在概率与潜在分布范围进行了预测。该模型预测精度较高，结果显示，斯科舍陆坡中部的内盆地区域是沃氏偕老同穴出现概率最高的区域，而陆坡外缘、芬迪海峡与东北海峡的出现概率较低。模型分析表明，底层水温是影响其分布的最关键环境因子。
尽管加拿大渔业与海洋部设立的两处海绵保护区保护了部分较为集中的沃氏偕老同穴种群，但该物种的绝大多数预测分布区域仍未得到保护（占比超过99%）。
对翡翠盆地的水文条件分析显示，与周边陆坡水域相比，沃氏偕老同穴栖息的海绵礁所在水团具有更高的温度与盐度。
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波动，平均底层水温的波动幅度可达8℃。
本研究表明，该物种能够在这种气候变率下持续存续，这或许能揭示其对未来气候变化的响应模式。