Rockall Bank
The verification exercise did not identify any of the 37 records of deep-sea sponge aggregations on the eastern part of Rockall Bank with high confidence (Table 2).
Video sequences from seabed tows conducted by Marine Science Scotland surveys in 2011 were examined that showed the patchy distribution of sponges along the seabed. Quantification of sponge encounters, combined with assemblage analyses e.g. using SIMPER, would provide a robust tool to determine whether sponges characterise the assemblages and if the assemblage is best described as a deep-sea sponge aggregation.
The verification exercise assigned a low to medium confidence level for these records, which according to the video seemed to be comprised of yellow and white lobose sponges on two types of substrata. The first were associated with bioturbated muddy sands, and the occasional cobble ground and boulder in waters 201–257m deep. Typically holothurians, anemones and the occasional Lophelia colony were present in these records. The second type of potential aggregation occurred approximately in the same depth band in waters 213–222m deep, but more on hard gravelly sands, cobbles and boulders, and were colonised by epifaunal organisms including Lophelia and gorgonians. Only sparse patches of sponges were observed in deeper areas of the survey beyond 775m water depth where boulders were draped in sediments.
Encrusting and lobose white and yellow sponges were also observed along the eastern flank of Rockall Bank (Howell et al 2009), on coarse sands, cobbles, boulders, on bedrock and biogenic debris in waters 421–578m deep. These assemblages supported a rich epifaunal community characterised by ophiuroids, Munida, Caryophyllidae, and serpulid polychaetes. However, the lower densities of sponges relative to indicator taxa of coral gardens (Long et al 2010) suggest these assemblages conform more closely to the Munida–Caryophyllia deep-sea mixed substratum assemblage associated with cold-water coral reef communities sensu Howell et al (2010), see Figure 5. Thus these likely correspond more closely to other habitats and are unlikely to represent deep-sea sponge aggregations.
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