_50 



worm population has been established, but evidence from long-term monitoring of worm 

 populations and life-history information indicate that periodic population "crashes" may be 

 characteristic of the species. Monitoring of populations of the congener R diversicolor in 

 the middle reaches of the Forth estuary (Scotland) over a 35 year period detected periodic 

 declines in abundance (McLusky and Martins, 1998). Similar patterns are evident in 

 abundances of intertidal populations of the same species from the German coast (Dorjes, 

 Michaelis, and Rhode, 1986). The periods of decline appear to occur at 5-6 year intervals 

 or multiples of this interval which coincides with the reproductive period of the species. 

 During reproduction the adult worms emerge from the sediment and swarm at the surface. 

 After reproduction the adults disperse or die resulting in periodic disappearance of adult 

 worms from the sediment. Nereis virens has an expected life span of seven years and 

 shares most of the life-history characteristics of R diversicolor including its reproductive 

 behaviors (Pettibone, 1963). While other factors cannot be excluded in accounting for the 

 absence of large worms, the simultaneous absence of large worms from both sites and the 

 coincidence of the time period with the clam- worm's life span suggest the 1998 data are 

 the result of normal interannual variation. Alternative explanations are obviously possible 

 and include over-harvesting or some non-site selective disturbance (e.g., pollutant release, 

 ice-scouring, etc.). There is no objective way of distinguishing between the potential 

 explanations from the present database. 



Finally, a healthy infaunal community has been established at the constructed flat. 

 The infaunal assemblage is similar to the reference area in respect to taxa richness (Figure 

 3-14) and abundance (Figure 3-15). Diversity of the Sheep Island sites is also comparable 

 to other North Atlantic intertidal assemblages (Table 4-1). Diversity, as measured by 

 Shaimon-Wiener's H', ranged from 1.18 to 2.88 at the constructed flat and 1.84 to 3.05 at 

 the reference area. These ranges closely correspond to H' values reported for other Maine 

 intertidal flats (e.g., Larsen and Doggett, 1991), Bay of Fundy flats (Ambrose, 1984) and 

 Massachusetts flats (Whitlach, 1977). Likewise, abundances at the Sheep Island sites 

 (11,000 to 95,000 animals/m^) are similar to those reported for other North Atlantic 

 intertidal flats (Table 4-1). Total biomass was lower at the constructed flat than the 

 reference area, particularly after 1992 (Figure 3-16), reflecting higher abundances of 

 oligochaetes and molluscs (Figure 3-17). While the similarity between the Sheep Island and 

 Beals Island biomass results, i.e., lower biomass at constructed flats, might seem to be of 

 concern, data from other New England intertidal flats indicates that these values are well 

 within normal bounds (Table 4-3). Bowen, Pembroke and Kinner (1989) measured biomass 

 at a number of intertidal flats in southern New England and reported values ranging from 6 

 to 612 g/m^ and averaging 164 g/m^. Biomass at the Sheep Island constructed flat ranged 

 from 76 to 181 g/m^ and averaged 125 g/m^, while the Beals Island constructed flat ranged 

 from 32 g/m^ to 127 g/m^ and averaged 72 g/m^. Average biomasses at the Sheep Island 

 and Beals Island reference areas were 285 g/m^ and 139 g/m^ respectively. Biomass 



Ecological Monitoring of a Constructed Intertidal Flat at Jonesport, Maine 



