SAND DOLLAR BEDS In eastern Canada, the common sand dollar (Echinarachnius parma) forms dense groups called beds that occur from shallow intertidal waters out to the offshore continental shelves (Figure 17). Contrary to their name, sand dollars are found in a range of sediment types, from coarse gravelly sand to fine silt. They feed on benthic diatoms (algae), organic and other small particles while burrowing using small tentacles. Sand dollars are a key species in the Atlantic because they are “bioturbators” — they rapidly disturb and mix sediments as they feed and burrow. This provides more oxygen deeper in the sediment, which allows more organisms to live there. On the Scotian Shelf, sand dollars are significant contributors to disturbing sediments on the ocean floor (second only to storms). Sand dollars can occur in dense aggregations (as many as 180 per square metre on Sable Island Bank), some of which have been considered in the identification of ecologically and biologically significant areas (EBSAs). Information on the distribution of sand dollars has been collected from multispecies trawl surveys, some scallop stock assessment surveys, and targeted research studies.
STATUS AND TRENDS •
Sand dollars are particularly abundant in the Bay of Fundy, eastern Scotian Shelf, Georges Bank, Gulf of St. Lawrence, and the Grand Banks.
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Undisturbed populations of sand dollars experience variation in abundance over time, but the location of beds is stable at larger spatial scales.
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Sand dollars are threatened by bottom trawling: one study on the Grand Banks showed a 37 percent decrease in population immediately after trawling. But because they may spawn more than once a year, the population can recover, at least in part of its range.
Sand dollars and winter flounder near Grandois on the Northern Peninsula, Newfoundland and Labrador in 2013 Fisheries and Oceans Canada, NL divers
Sand dollars and winter flounder near Grandois on the Northern Peninsula, Newfoundland and Labrador in 2013. Credit: Fisheries and Oceans Canada, NL Divers.
DISTRIBUTION OF SAND DOLLARS IN AREAS OF THE SCOTIAN SHELF
Figure 17 : Distribution of sand dollars in the Scotian Shelf bioregion from DFO multispecies trawl surveys (1999–2015) and scallop stock assessment surveys (1997, 2007). Sand dollars are particularly abundant in the Bay of Fundy, eastern Scotian Shelf, Georges Bank, Gulf of St. Lawrence, and the Grand Banks. (Reproduced with permission from Beazley et al. 2017) CANADA’S OCEANS NOW: ATLANTIC ECOSYSTEMS
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