At present, the application of these mechanisms 

 to our sample sites at WP and FI is premature; 

 one year of 3-unit operation is insufficient to de- 

 termine whether thermal incursions to these sites, 

 of short duration, are great enough to influence 

 the Teredo navalis populations. We have not 

 identified a non-native shipworm at WP or FI, 

 even though Teredo bartschi has been found in 

 the MNPS effluent quarry since 1975. 



In contrast, the woodborer populations at 

 effluent sites were clearly affected by 3-unit oper- 

 ating conditions; panels at EB and ES have shown 

 higher Teredo bartschi densities and greater wood- 

 loss in May-Nov, Aug-Feb, and Feb-Aug since 

 Unit 3 began operation. However, effluent water 

 temperatures have not increased during 3-unit op- 

 eration; average AT's have remained within 2-unit 

 operation ranges. Therefore, the operational effect 

 must be related to a factor other than temperature. 



A non-thermal effect resulting from start-up of 

 Unit 3 is increased flow and turbulence in the 

 Millstone Quarry. Teredo larvae are relatively 

 dense, and usually settle near the bottom (Graves 

 1928; Scheltema and Truitt 1956; Turner 1966; 

 Nair and Saraswathy 1971). The increased tur- 

 bulence may be suspending the larvae in the water 

 column long enough to allow them to attack pan- 

 els hung from the floating lab. 



We have observed changes in the densities of 

 Teredo navalis populations since Unit 3 began 

 operation, and have postulated mechanisms 

 through which these changes might have occurred. 

 However, owing to the limited 3-unit operation 

 database, and the high degree of natural variability 

 typical of biological systems, at present we do not 

 have sufficient information to assess whether the 

 observed increases in shipworm density and wood- 

 loss at WP and FI are related to MNPS operation. 

 Further monitoring will increase our understand- 

 ing of the system, and allow us to make that 

 assessment. 



Distribution Study 



Materials and Methods 



The distribution of shipworms in the MNPS 

 effluent mixing zone was assessed, using their 

 abundance in panels placed 100, 500, and 1000 

 m from the Millstone Quarry cuts (Fig. 1). At 

 each location, five panels were attached to each 

 of three modified lobster pots, deployed on the 

 bottom in trawl lines (Fig. 12). Panels were first 

 set out in May 1985. In November 1985, three 

 panels from each pot were collected, and replaced 

 with fresh panels (the remaining two panels in 

 each pot served as a source community for 

 overwintering shipworms and larvae). In May 

 1986, all panels were collected, and replaced with 

 new panels. Pased on the severe wood-loss seen 

 in panels collected in November 1985, sample 

 design was modified to provide a 5-month expo- 

 sure period (May-Oct), including the time of max- 

 imum settlement and growth, and a 7-month ex- 

 posure period (Oct-May), comprising months of 

 low infestation. The trawl-line placed at 100 m 

 in May 1986 proved impossible to maintain; peo- 

 ple fishing in the area of the discharge frequently 

 moved the pots or cut the buoy lines. Therefore, 

 data from 100 m during the May-Oct 1986 expo- 

 sure period are excluded from this report. Begin- 

 ning in October 1986, pots at 100 m were 

 unbuoyed, deployed and collected individually by 

 divers. 



Six of the nine panels collected from each dis- 

 tance in October (or November of 1985) were 

 each cut into six segments (Fig. 12). A different 

 section of each panel was examined; all shipworms 

 found were removed and identified. Woodborer 

 abundance was determined as a composite total 

 for each distance. 



Shipworm attack was minimal in panels col- 

 lected in May; to quantify infestation, all panels 

 were examined by means of X-ray photography, 

 using the techniques described in the previous 

 section. If shipworms were present, they were 

 removed and identified. 



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