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架上的翡翠盆地（Emerald Basin），是全球独有的玻璃海绵（glass sponge）Vazella pourtalesi的聚集分布区，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破坏。两处保护区总面积达259平方千米。为明确该海绵礁当前未受保护的比例，研究团队基于存在-缺失观测记录，采用随机森林（random forest）建模方法，对斯科舍陆架上Vazella pourtalesi的存在概率与潜在分布范围进行了预测。该随机森林模型具有较高的预测准确率，结果显示Vazella pourtalesi的最高出现概率分布于斯科舍陆架中部的内盆地，而在陆架边缘、芬迪海峡与东北水道区域的出现概率较低；模型中底层水温是影响其分布的最重要环境因子。尽管两处加拿大渔业与海洋部海绵保护区覆盖了部分较为重要的Vazella pourtalesi聚集区，但其预测分布范围内仍有超过99%的区域未受到保护。对翡翠盆地的水文条件分析显示，Vazella pourtalesi海绵礁所在的水团相较于周边陆架水团，温度更高、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，该区域存在显著的数十年尺度气候变异性，底层平均水温波动幅度达8℃。研究显示，该物种在这种气候变异性下仍得以存续，这或可揭示其对未来气候变化的潜在响应模式。