MEGAFAUNAL POPULATIONS IN LYDONIA CANYON 

 WITH NOTES ON THREE OTHER NORTH ATLANTIC CANYONS 



Dr. Barbara Hecker 



Lament Doherty Geological Observatory 



Palisades, NY 



Lydonia Canyon is a relatively narrow canyon that incises Georges Bank 

 approximately 11 mi north of the shelf-slope break. It has a narrow sediment- 

 covered axis flanked by steep walls with massive exposures of outcrop and 

 talus-strewn slopes. 



Megafaunal populations in Lydonia Canyon were surveyed photographically 

 during 16 camera sled tows and 17 Alvin dives between May 1979 and September 

 1982. Nearly 115,000 square meters of sea floor, between 130- and 2,330-m 

 depth, were analyzed. More than 750,000 animals were identified. The analysis 

 included data on water depth, surficial geology, current indications, species 

 identification, and abundance. The area viewed was estimated for most of the 

 pictures since flat terrain was rarely encountered. The Alvin dives were used 

 to obtain data in very steep regions and collect "voucher" specimens for 

 better taxonomic identification. 



RESULTS 



Faunal abundance was much greater in the canyon than at comparable depths 

 on the slope. Total megafaunal abundance in the canyon was very high (up to 

 30 individuals/m^) at shallow depths, and intermediate at mid-slope (5 

 individuals/m^) and lower slope (7 to 8 individuals/m^) depths. Highest 

 concentrations were along the canyon axis, but abundance was also high on the 

 flanks, especially in areas of outcrops or boulders. Between 350 to 450 m in 

 the axis there were very high concentrations of a sea pen {Pennaula aculeata) 

 and brittle stars {Ophiura spp); other high concentrations were at 800 to 

 1,000 m (mostly hard-substrate corals) and below 1,600 m (a different brittle 

 star {Ophiomusirium lymani)). 



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