In the first year juvenile mussels have been observed to reach a length of 0.8 

 to 1.6 inches (20 to 40 mm) in Massachusetts (Field 1922). In Denmark, 

 Rasmussen (1973) found growth of 1 inch (25 mm) in the first 4 months. In the 

 Damariscotta estuary, average growth of cultivated mussels for 1 year is 

 approximately 2 inches (50 mm; Incze et al. 1978); however, MARITEC (1978) 

 found natural populations of mussels in Maine to be 2.4 inches (60 mm) at 8.2 

 years and 2.8 inches (70 mm) at 9.5 years. 



The diet of mussels consists of phytoplankton and detritus filtered from the 

 surrounding water (TRIG0M 1974). 



Habitat Preferences 



West of Schoodic Point (regions 1 to 5) , mussels of commercial size are most 

 abundant approximately 3.2 feet (1 m) above and below mean low water level, 

 whereas most beds in the Jonesport area (region 6) are above mean low water 

 level (MARITEC 1978). Subtidal beds are located almost exclusively in areas 

 with good currents, especially around offshore islands and in the mouths of 

 estuaries. These beds are far less numerous than intertidal beds. 



Pelagic larvae live in the water columns of estuarine and marine systems. 

 Optimal conditions include an adequate food supply, salinities between 15 and 

 40 ppt and temperatures ranging from 41 to 68 F (5 to 20° C). 



Juvenile and adult mussels are found in every type of intertidal habitat 

 present in coastal Maine. Juveniles are extremely abundant on rocky shores, 

 while both adults and juveniles are plentiful in low intertidal areas on 

 gravel beaches, and as part of fouling communities on pilings and on flats, 

 particularly mud flats. Mussels are especially abundant in areas of high 

 water flow such as tidal falls. The commercially harvested beds are 

 principally found on intertidal mud flats and unconsolidated sediments in 

 shallow subtidal waters. 



Factors of Abundance 



Mussel abundance in coastal Maine is determined by a number of natural 

 limiting factors which include predation, competition, and climatic factors. 

 Common predators include sea ducks, gulls, whelks, starfish, crabs, and bottom 

 feeding fish. The dog whelk ( Thais lapillus ) , by preying on juveniles, may 

 limit mussel abundance on rocky shores, particularly in the more protected 

 areas (Menge 1976) . Eider ducks have been reported to eat approximately 425 g 

 (1 pt) of mussels in one day (Field 1922). Up to 80% of the stomach contents 

 of these ducks in the summer is comprised of juvenile mussels (Graham 1975). 



The most significant competition among blue mussels is for food and space 

 between individuals. As younger mussels settle and accumulate on established 

 beds, older ones are buried and may be smothered. Theisen (1972) found that 

 mussels regularly clean their shell surfaces with their foot, and he suggested 

 that this cleaning action wards off other mussels trying to settle on them. 

 Mussels may also move within the bed, out from under other mussels to a more 

 exposed position. 



Waves generated during northeast storms, which occur in Maine in the fall, 

 winter, and spring, cause high mortality rates in mussels. Some storms 



12-8 



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