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海斯科舍陆架的翡翠盆地（Emerald Basin），是全球独有的玻璃海绵（glass sponge）沃氏偕老同穴（Vazella pourtalesi）聚集区，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，以保护该海绵礁免受底拖捕捞活动的破坏，两处保护区总面积达259平方千米。为明确该海绵礁当前的未受保护程度，研究团队基于出现-缺失（presence-absence）记录，利用随机森林（Random Forest）模型，对斯科舍陆架的沃氏偕老同穴（Vazella pourtalesi）存在概率及潜在分布范围进行了预测。该随机森林模型预测准确率较高，结果显示斯科舍陆架中部内盆地为沃氏偕老同穴出现概率最高的区域，而陆架坡折带、芬迪水道与东北海峡的出现概率相对较低。模型结果表明，底层水温是影响其分布的最关键驱动因子。尽管上述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沃氏偕老同穴聚集区，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，沃氏偕老同穴海绵礁所在的水团相较于周边陆架水体，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显示，该区域存在显著的多年代际气候变率，平均底层水温波动幅度达8℃。研究证实，该物种在这种气候变率下仍得以存续，这或可为预测其对未来气候变化的响应提供科学依据。