RAPID: Role of Ephemeral Bottom Roughness Patches in Unpredictable Recruitment of Surfclams on the Continental Shelf

Surfclams must settle and recruit in large numbers to produce a year-class of adult clams because of heavy predation pressure on new recruits. In sandy sediments, dense but ephemeral shell-hash patches provide bottom roughness that may affect the fluxes of larvae and food to the bed and provide recruits with shelter from predators. The objective of this RAPID project is to determine how the presence and persistence of ephemeral shell patches that alter the bottom roughness affect the recruitment, growth, and survival of surfclams. This rapid-response study capitalizes on a rare, high-density settlement and recruitment event of surfclams which occurred last year at the Long-term Ecosystem Observatory (LEO-15) in the Mid-Atlantic Bight. The investigators will survey the Beach Haven Ridge area of LEO-15 in the spring of 2009, using an autonomous underwater vehicle (REMUS) equipped with Side Scan Sonar to identify areas of shell accumulation, to chart their location and extent, and to measure turbulence above and outside the areas. Weekly core-sampling by divers and surfclam size measurements will be used to determine and compare surfclam survival and growth inside and outside of shell patches. Surveys and sampling will be repeated in the fall of 2009 to examine the persistence of the shell areas and to determine how these shell patches affect abundance and growth of 2008 and 2009 summer recruits.

This research will enhance knowledge of the ephemeral nature of shell aggregations, and their effects on surfclam settlement, mortality, and early growth. These results will contribute to understanding the morphodynamic and physical processes influencing surfclam population dynamics.

Results of this work will inform habitat-based management strategies and will aid in monitoring and management of an ecologically and commercially important shelf species. Undergraduate students will be involved in this work through the NSF-funded REU (Research Internships in Ocean Sciences) program. Results will be presented in a peer-reviewed scientific journal and at a national scientific conference.