Skottsberg ( 19O6 , 1941, 1953) bas analysed the general c h a r a c te r is tic s o f the marine v eg eta tio n in r e la tio n to the p h ysical fa c to r s o f the environment» In the la t e r o f th ese p u b lica tio n s he considered the term e l it t o r a l to be b est reserved fo r the b e lt com p le t e ly devoid o f b en th ic vegetation® E a r lie r , Kjellman (187T) had d e fin e d -it as the region from a depth o f 3?m (the lim it o f h is lower s u b - litt o r a l b e lt ) down to the lim it o f attachment o f m acroscopic
algae® This lo w er-lim it according to Zaneveld ( 1966) l i e s at the rath er in cr ed ib le depth o f 668m in the Ross Sea. More w ill be sa id about t h is p oin t later®
Of a ll a sp ects o f plant m etabolism , p h otosyn th esis shows the most prominent v a r ia tio n under the d ic ta te s o f the immediate environment
(T a ilin g , 1961)0 As near natural con d ition s as p o ssib le i s an e s s e n tia l p rere q u isite of any attem pt to measure the e ffe c t of environmental
fa c to r s on p h otosyn th etic r a te s o f marine algae» Once such data has been obtained i t i s then p o ssib le to a sse ss how important p h otosyn th esis i s during the growth period o f the plant®
/' " The unique value o f aq u atic p lan ts for illu s t r a t in g photo- sy n th e tic p rocesses was f i r s t r e a lis e d in the 1920's by marine and fresh water b io lo g is ts , e ,g. G ail (1922), Ruttner (1926), Gaarder & Gran (l9 2 7 ) and M arshall & Orr ( 1928). G a il, fo r example, determined the maximum lev e l
o f p h o tosy n th esis, by in s it u measurements o f some red and brown s u b -litt o r a l algae and re la te d h is data to depth and light® The ’’ maximum amount o f p h otosyn th esis o f the brown algae occurred at a
depth o f 1-8m w h ilst th at o f the red occurred at 1O-g^m. Both depths were decreased by cloudy weather or choppy w ater. Tikliovskaya (1940) showed th a t p h otosyn th esis o f Laminaria saccharine changed markedly m th depth and season and th at growth could s t i l l take p lace during the p olar ' n ig h t in December and January when no p h otosyn th esis occurred® Sargent
and Lantrip (1952) working m th Macrocys t i s p yrifera and using in s it u measurements o f p h o tosyn th esis showed the n e c e ssity o f tra n slo o a tio n to .supply organic m aterial to the growing tip s o f the p lan t which were found ‘ \ to be beloif the compensation point® B lin ks (l95 1j 1955) a,nd Eanwisher
( 1966) report on._the p h otosyn th etic r a te s of l i t t o r a l and s u b -litto r a l algae in variou s e c o lo g ic a l s itu a tio n s w hile P rin ts (1939)? Levring
( 1947? 1966, 1967) and Drew ( 1969b) have, in the p rocess o f studying the zonation o f s u b -litto r a l a lg a e , carried out in s it u measurements o f photo sy n th esis in sev era l genera® There have been ex ten siv e stu d ies on the p ro d u ctiv ity o f marine phytoplanlcton, reviewed by S trick lan d (1958), u sin g
14
both th e Winkler oxygen technique and the G technique d evised by Steem am i-Nielsen (1952)®
Regarding the m acroalgae, once in s itu stu d ie s o f p h otosyn th esis such a s those mentioned above have been made i t i s p o ssib le to a s s e s s the im portance o f p h o tosy n th esis during the growth period o f the plant®
Neushul ( 1963) suggested th at aphotic con d ition s e x iste d under th ick ic e covep, but la te r work o f Zaneveld ( 1966) disproved this® He found th a t 1®4^ o f in cid en t li g h t , i®e® a ca lcu la ted 13 fo o t-c a n d le s penetrated to a depth o f 20m under a 2m th ick ic e cover w ith only a tra ce of snow® I t ' should be emphasised th a t th ere was only a trace o f snow overlyin g the
..13
't-' i
ic e a t th a t tim e; th e amount o f lig h t p en etratin g the ic e i s stro n g ly dependant on the s ta te o f the ic e surface idiich may be ov erla in by snow or melt ponds, satu rated with m elt w ater, drained or p olish ed by the wind (Maykut & U n terstein er, 1971)* Only long term stu d ies in v o lv in g in s it u measurements o f p h otosyn th esis can determine the e f f e c t s o f such v a r ia b le environm ental factors®
I I PHOTOSYNTHESIS AND RESPIRAKON - AN ASSESSMENT OF THE METHODS