shallow water population of L. digitata . Because the 

 physiological characteristics of the two populations will reflect 

 both genetic differences and phenotypic acclimation to the light 

 levels at the two sites, reciprocal transplants were performed in 

 order that comparisons could be made between sporophytes from the 

 two populations which had been exposed to similar irradiance 

 levels. These experiments were performed during the summer 1987 

 curises of the RV Powell and RV Seward Johnson in the Gulf of 

 Maine. 



METHODS 



Two populations were studied: a shallow water Laminaria 

 digitata (Huds.) Lamour. population growing 1 m below mean low 

 water at Thread-of-Life in Maine, and the Ammen population 

 described previously (Vadas and Steneck, 1988) growing at 30 m at 

 Ammen rock pinnacle. Initial samples were taken from these sites 

 in late June 1987. 10 plants from each group were transplanted to 

 each of three transplant sites: 1 m and 15 m at Pemaguid (a 

 coastal site close to Thread-of-Life) and 30 m at Ammen rock 

 pinnacle. Transplants had a blade length of between 30 and 60 cm. 

 Plants were transplanted by opening the weave of short lengths of 

 polypropylene rope to admit the holdfast and stipe of tagged 

 plants. The polypropylene ropes were then attached to an anchored 

 buoyed nylon line. Transplants at the coastal site were retrieved 

 in late August 1987, immediately prior to the second cruise to 

 Ammen rock. The 30 m Ammen transplants were retrieved in early 

 September 1987. Plants were collected, and trasplant 

 manipulations performed, by SCUBA divers. Plants were 

 transported between the two coastal and Ammen sites and to the 

 laboratory at the University of Maine (Orono campus) in cold (5°C) 

 seawater in large insulated coolers. 



Growth of the transplanted Laminaria was monitored by the 

 hole punch technigue of Parke (1948) . Five sporophytes were 

 collected from each field site in June and taken to Orono for 

 measurements of initial photosynthetic characteristics, activities 

 of enzymes of carbon and nitrogen metabolism and biochemical 

 analysis. Similar measurements were made on subsamples (n=5) of 

 both plant groups after growth at the transplant sites. In the 

 case of plants from the 1 and 15 m coastal sites these 

 measurements were made at Orono, with the measurements on the 30 m 

 Ammen transplants being made onboard the RV Seward Johnson . 



Photosynthetic and respiratory measurements were made on 1.95 

 cm diameter discs punched from the blade 15-25 cm above the stipe- 

 blade transition. Discs were held overnight (18 hr) in aerated 

 seawater at 5° C and a photon flux density of 50 umole 

 photons. m' 2 .s' 1 in a 16:8 L:D photoperiod. This procedure allows 

 wound healing to occur (Bidwell and McLachlan, 1985) . Discs of L. 

 digitata and Ammen Laminaria plants both release copious 

 guantities of mucilage immediately after being cut. Discs were 

 placed in the reaction chamber of a calibrated Rank oxygen 



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