Date Published: October 24, 2018
Publisher: Public Library of Science
Author(s): Lindsay Beazley, Zeliang Wang, Ellen Kenchington, Igor Yashayaev, Hans Tore Rapp, Joana R. Xavier, Francisco Javier Murillo, Derek Fenton, Susanna Fuller, Andrew Davies.
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.
Deep-sea sponge-dominated communities have gained increasing attention in recent years from both an ecological and conservation perspective. Growing evidence not only suggests that these habitats are widely distributed across the deep sea globally [1–2], but that they also play key functional roles, directly or indirectly, in delivering a number of ecosystem goods and services. This includes, but is not limited to, habitat-provision [3–10], biodiversity enhancement [11–15], and biogeochemical cycling [16–20] (see also the review by ).
Observational data of V. pourtalesi indicated that this species aggregates on the flanks of the two deep-water basins that comprise Emerald Basin, with the densest concentration located between the main and northern basins and to the west of the area known to fisherman as ‘The Patch’ (Fig 3). This concentration is mostly captured by DFO’s Emerald Basin Vazella Conservation Area. A second notable concentration was situated on the southwestern portion of the main basin adjacent to Sambro Bank, and is partially protected by DFO’s Sambro Bank Vazella Conservation Area. V. pourtalesi was found in lower concentrations along the saddle between Emerald and LaHave Banks in the Scotian Gulf, and in the Northeast and Fundian Channels leading to the Gulf of Maine. V. pourtalesi was generally absent from the shelf, Bay of Fundy, and in off-shelf waters to ~1850 m depth. The overall depth range of presence observations was 87 to 498 m (based on Canadian Hydrographic Service Atlantic Bathymetry Compilation, 500-m bathymetry). The deepest records were found along the shelf break at the mouth of the Scotian Gulf and in the Northeast Channel. The shallowest record of this species was from Misaine Bank at 87 m depth. While some records are associated with high-slope areas (11° in the Northeast Channel), the densest sponge grounds occurred in areas of low topographic relief (0.04 to 3.20° in Emerald Basin).
Our study represents the first description in the primary literature of a monospecific sponge ground formed by the glass sponge V. pourtalesi in Emerald Basin, Nova Scotia, Canada. The Vazella sponge grounds in Emerald Basin are globally unique for this species, which to date has not been reported to form large aggregations in other areas of its distribution, and are also unique for the northwest Atlantic where ostur-type sponges are typically the dominant sponge-ground type [28,77,91–92].