Journal Molluscan Studies Advance Access originally published online on May 6, 2009
Journal of Molluscan Studies 2009 75(3):215-222; doi:10.1093/mollus/eyp019
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Species-specific variation in larval survival and patterns of distribution for the blue mussels Mytilus edulis and Mytilus trossulus in the Gulf of Maine
1 Cummings School of Veterinary Medicine, 200 Westboro Road, North Grafton, MA 01536, USA; and 2School of Marine Sciences, University of Maine, 5751 Murray Hall, Orono, ME 04469, USA
Correspondence: P.D. Rawson; e-mail: prawson{at}maine.edu
 |
Abstract |
|---|
A broad zone of sympatry between two morphologically and ecologically similar blue mussels Mytilus trossulus (Gould) and M. edulis (L.) extends from the Canadian Maritimes into the Gulf of Maine. The zone boundary and the southern range limit of M. trossulus coincide with the position of the Eastern Maine Coastal Current (EMCC). This current has not been recognized as a biogeographic boundary. However, the flow field associated with the EMCC essentially divides the eastern and western Gulf during the part of year when mussel populations in the eastern portion of the Gulf are reproductively active and thus may be a hydrodynamic barrier to the westward dispersal of M. trossulus larvae. Alternatively, a strong gradient in water temperature associated with the EMCC may create a physiological barrier to M. trossulus larvae. We examined spatial variation in the abundance of M. trossulus and M. edulis along the coast of Maine using two diagnostic DNA-based markers. Although we detected M. trossulus in mussel populations in offshore locations in central Maine that were directly in the path of the EMCC, the abundance of this species declines dramatically at sites beyond the influence of this current. Variation in the abundance of adults, however, cannot differentiate between the effects of the EMCC on larval transport vs physiological tolerance. Thus, we also conducted a temperature challenge experiment investigating the species-specific variation in larval survival at temperatures ranging from 5°C to 20°C. We found that larval mortality was generally higher for M. trossulus relative to M. edulis larvae when exposed to 20°C early during development. These results suggest that differences in larval thermal tolerance help to structure the southern range limit for M. trossulus in the Gulf of Maine.
(Received 19 December 2008; accepted 6 March 2009)