Pomeroy: Within the optimal range. 



Odum: And thus both seasonally and vertically and with the tide you 



have high photosynthesis when this happens. Now don't these 

 diatoms move in and out of the mud as you have described them? 



Pomeroy: The migration is pronounced on the bare strand at the bottom of 



the levees and on the mud banks around the creeks. When you 

 get up into the Spartina and up into the marsh proper, I cannot 

 detect any migration up in there; so I think that becomes rela- 

 tively unimportant when you are talking about the marsh as a 

 whole . 



Odum: In other words you wouldn't think that the plants would seek 



their own light level? They wouldn't have to go very far. 



Pomeroy: They do not seem to be. They seem to be doing exactly the 



opposite, because they are coming up when the sediments are 

 exposed. Maybe they are fighting each other and trying to 

 reach the top, but that does not seem reasonable to me. There 

 is something else controlling it, 



Odum: The mechanism is there but the plants are doing what is not 



good for them. 



Pomeroy: The mechanism is there and if, while they have migrated to the 



surface, you put a box over them, they will go right down. Or- 

 dinarily they won't go down until an hour to half an hour before 

 the tide comes back, but cover them up and they will go right 

 down. You can check this by putting black polyethylene right 

 on the top. That heats them so rapidly they are killed. Then 

 you have a control, and you can peel the polyethylene off and 

 you have a nice brown or green patch as the case may be to 

 c ompare with. 



Moul: At the base of the Spartina do you have here a skin of blue - 



green algae, like we have on the Jersey coast? 



Pomeroy: Yes, and during the winter and early spring we get quite a lot 



of blue -green algae up on the upper parts of the levee and 

 back in the marsh. 



Moul: That is not subject to this migration? 



Pomeroy: As far as I have found, it is not, and 1 think as far as produc- 



tion is concerned that they are probably less important than the 

 diatoms. I have made a few measurements on it and there is 

 production there during a short time of year when they are very 

 evident, but it is a short period, 



92 



