Sponge communities in the eastern Canadian Arctic: species richness, diversity and density determined using targeted benthic sampling and underwater video analysis

The sponge diversity of the eastern Canadian Arctic remains largely unknown. Sponges of the three marine ecoregions which make up the eastern Canadian Arctic and sub-Arctic are described from collections using remote operated vehicle (ROV), box core, and Agassiz trawl. In total, 161 sponges were collected between 2015 and 2017, and 60 different species were identified. ROV surveys covered a range of benthic habitats, but sponges seen in video could only be identified to morphotypes. Twenty-seven distinct sponge morphotypes were identified from ROV surveys of six sites in the study region, but only fifteen of these were commonly encountered and unambiguously identified at the different sites. Transects were carried out in a non-linear manner due to ROV limitations, and covered varied benthic habitats ranging from soft sand to steep bedrock cliffs. The highest number of species identified from specimens collected was in the Northern Labrador marine ecoregion (46 species), while the highest number of morphotypes identified from ROV video was in the Baffin Bay/Davis Strait ecoregion at a dive site near Pond Inlet (17 morphotypes). Several species collected and morphotypes counted were found across different ecoregions, but smaller sponges could not be identified from ROV video. Sponge density was estimated from exploratory ROV video and ranged from 0.008 ind. m−2 in Lancaster Sound to 0.371 ind. m−2 at a site near Pond Inlet. The combined collections and video analysis show the importance of using different collection and observation methodologies to properly understand the biodiversity of benthic habitats that are difficult to access.