β Scribed by J. Ramus; F. Lemons; C. Zimmerman
No coin nor oath required. For personal study only.
We c o m p a r e d the effect of habitat and water depth on the l i g h t -h a r v e s t i n g pigment content for A s c o p h y l l u m n o d o s u m and Fucus vesiculosus at two n e a r -s h o r e stations in Long Island Sound (USA). Excised pieces of seaweeds were attached at depth intervals to a v e r t i c a l l y buoyed line, and left in situ for 7 days. For comparison, fronds were collected from sun and shade habitats in the littoral zone. The three major antenna (light-harvesting) pigments increased in c o n c e n t r a t i o n with depth or shade. Chlorophyll c to a ratios r e m a i n e d stable at about 0.2. F u c o x a n t h i n to c h l o r o p h y l l a ratios d e c r e a s e d by 20 to 30% with depth or shade. A l t h o u g h pigment c o m p o s i t i o n for the two r o c k w e e d species was equivalent, the m a x i m u m p h o t o s y n t h e t i c p e r f o r m a n c e of F. vesiculosus exceeded that of A. nodosum by a factor of 2, w h i l e the compensation depths for 4 m -a d a p t e d A. nodosum and F. vesiculosus under natural limiting light conditions were equivalent. Plants held at 4 m had higher p h o t o s y n t h e t i c rates compared with plants held at 0 m, no matter the depth of measurement. Indirect evidence indicates that the enhanced p h o t o s y n t h e s i s of 4 m -a d a p t e d plants is due not only to higher c o n c e n t r a t i o n s of antenna pigments but to other p h y s i o l o g i c a l factors as well. We c o n c l u d e that the clearly d e l i n e a t e d v e r t i c a l d i s t r i b u t i o n of these two canopy species, the F. vesiculosus zone over the A. nodosum zone, is not determined by light q u a n t i t y or quality, but by biotic factors as e v i d e n c e d by the e x p e r i m e n t s of M e n g e w h i c h are cited herein.
π SIMILAR VOLUMES