electrode together with 5 ml of millipore filterd (0.45 um pore 

 size) seawater. Temperature was maintained at 15° C by a 

 refrigerated thermostatic circulator connected to the water jacket 

 of the electrode chamber. The output of the oxygen electrode was 

 recorded on a strip chart recorder. The sensitivity of the 

 measurements was increased by setting the chart recorder at 1 mV 

 rather than 10 mV (the full scale output of the Rank electrode) , 

 offsetting the zero with a Baily RC-10 recorder calibrator. 



The oxygen content of the filtered seawater was adjusted to 

 50-60% of saturation by sparging with nitrogen. Respiration rates 

 were measured by enclosing the reaction chamber in a double layer 

 of thick black cloth. Once a stable respiration rate was achieved 

 the disc was illuminated with successively higher photon flux 

 densities from 1.0 to 600 umole photons. m' 2 . s" 1 supplied by a 

 slide projector. Photon flux densities were varied by means of 

 Schott glass neutral density filters. Light levels were increased 

 once a stable rate of oxygen flux was achieved at the previous 

 photon flux density. The entire process took approximately 45-60 

 min. There was no evidence of photorespiration or nutrient 

 limitation. Measurements were corrected for oxygen consumption by 

 the electrode. Determinations were made on a single disc from 

 each of 5 replicate plants. 



Activities of the key Calvin cycle enzyme ribulose-1, 5- 

 bisphosphate carboxylase oxygenase (RUBISCO) and the key nitrogen 

 assimilatory enzyme nitrate reductase (NR) were measured as 

 described previously (Davison and Davison, 1987; Davison, 1987). 

 Pigments were analyzed on discs used for photosynthesis 

 measurements by extraction in DMSO and methanol as described by 

 Seely et al . (1972). A further series of discs were extracted 

 with hot 90% ethanol for the determination of mannitol, amino-N 

 and N0 3 as described previously (Davison and Davison, 1987) . 



Statistical analysis was performed on the data using 1 or 2 

 way ANOVA. Non-normal data was analyzed by ANOVA on data ranked 

 using the Kruskal-Wallis procedure. Comparison of means was based 

 on the Student Newman Keuls test. All statistical procedures were 

 done using SAS version 5.16. 



RESULTS 



Growth rates of transplanted Ammen and coastal Laminaria are 

 shown in Figure 1. Ammen plants transplanted to the 1 m coastal 

 site grew significantly more slowly than coastal plants (0.082 vs 

 0.165 cm. mo' 1 , respectively). Ammen plants grew significantly 

 faster at the 15 m site where both groups of plants achieved 

 similar rates of growth (0.129 - 0.156 cm.mo' 1 ) . Coastal plants 

 grew slowest (0.038 cm.mo' 1 ) at the 30 m Ammen site. Although 

 Ammen plants grew at 0.066 cm.mo' 1 at the 30 m site there was no 

 significant difference between the two groups of plants. However, 

 when growth rates at this site were compared in terms of linear 

 increase per month, significant differences were evident, with the 



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