Symposium Abstract: Bottom Trawling Effects on Cerianthid Burrowing Anemone Aggregations and Acadian Redfish Habitats in Mud to Muddy Gravel Seabeds of the Stellwagon Bank National Marine Sanctuary Region, Gilf of Maine (Northwest Atlantic)
P. C. Valentine, J. B. Lindholm, and P. J. Auster
Burrowing cerianthid anemones (Cerianthus spp.) occur in mud, gravelly mud, and muddy gravel in the Gulf of Maine. The non-retractable anemone tubes commonly extend 15 cm above the seabed, form dense aggregations (up to 10’s m-2), and provide habitat for Acadian redfish (Sebastes fasciatus). Video sampling shows that anemones are common in untrawlable areas such as the mud bases and the muddy tops of gravel banks but are less common than expected in heavily fished mud basins. Video observations were conducted in August 2001 in two settings: ‘gravel window’ areas on mud basin floors where cobbles and boulders on the tops of gravel mounds are almost covered by mud; and the mud floor and mud to muddy gravel walls of a long narrow basin. Video imagery shows trawling occurs predominantly in mud around the gravel windows and on the mud floor and lower walls of the narrow basin. Video transects across these features ranged up to more than a kilometer in length. Quantification of 20-meter seabed segments shows that trawling is least intense and anemones and redfish are most common on the gravel windows and on the muddy gravel middle and upper basin walls. These observations suggest that either: (1) trawling on mud has modified the distribution of cerianthids by direct removal; (2) trawling has modified the mud seabed so cerianthid recruitment has declined significantly; (3) untrawled mud in open basins is not conducive to cerianthid recruitment. Variations in the distribution of cerianthids may have important implications for the successful recruitment of redfish.