SUSTENTACIÓN Y FORMULACIÓN DE LA PREGUNTA DE

L* hyperborea and 11.3 kg fresh w eight, m a t 9°1m; LAI valu es were

r e s p e c tiv e ly 7»3 and 3.4* The giant kelp K acrocystis develops very large i biom asses o ff the co a st o f C a lifo rn ia and in the Indian Ocean. Biom asses ■ o f up to 22 kgonT^ (fresh w eight) have been reported o f f C a lifo rn ia (Mann, 1973)

-”2 —2

and 95 to 606 kg. m w ith an average of 140 kg. m " in the Indian Ocean ■ —2 (N orth, 1971)0 The n et annual p ro d u ctiv ity in C a lifo rn ia was 4OO to 820 gC.m

(Clendenning, 1971)° :

I n te r tid a l seaweeds such as Fucus and Ascophyllum may o c c a sio n a lly have ra tes of production comparable with th ose o f k e lp s. In Nova S co tia

th e fresh -w eigh t may be as high as 32 kg.m (MacFarlane, 1952) w ith an ; estim ated productivity o f 64O to 68O gC.m ^ .yr (T ea l, 1962). I t has been :

shown th a t Fucus and Ascophyllum can double th e ir weight in 5 to 10 days and i

a n atu ral population xvas able to f i x more than 10 gC.m .d (Kanwisher, 1966) 0. No d e fin ite con clu sion s about the e f fe c t o f depth on th e biomass o f P h yllog ig as can be made, due to the sparse d is tr ib u tio n of the p la n ts - (see Map, Chapter 2 ). In L. hyperborea , Kain (1971b) has shown th at the

d e n sity decreases ivith in crea sin g depth, as has been observed in t h is stud y, . but th e maximum s iz e o f the p la n ts becomes sm aller. Luning (1970) a ls o rep orts' a decrease in s iz e with depth, though the depths range much sm a ller, . 2- 61TI0 In P h y llo g ig as , the deeper p la n ts xjere seen to be much more m assive ; than th ose in shallow er w ater. In some a r e a s,fo r in sta n ce the I s le o f Man, , ' the low er lim it o f th e p la n ts i s determ ined by grazing pressure a c tin g on

the establishm ent o f the sp e c ie s ratlier than i t s la te r growth ra te (Kain, 1963) Here, the d eep est p la n ts are r e la t iv e ly large and th ere i s very l i t t l e

av a ila b le at present on th e growth r a te s of-deeper specim ens o f R h yllogigas '-or on the e f fec t s o f grazing. Large numbers o f sea-u rch in s have been seen

in deeper areas where P h y llo g ig a s was present but nothing i s knom o f th e ir feed in g h a b its. Kain (1971b) a lso rep orts deep p opulations in south-west

Norway o f L* hyperborea c o n sistin g o f sm all slow-growing plants* Conway (196?) comments on the v a r ia tio n in s iz e o f L. hyperborea from variou s depths on

Carsaig Isla n d , A rgyll. M assive development was observed from 5 to 10m, : which had been noted p rev iou sly by h itch in g (1941) and dying out at about I6m, i a fig u r e which agrees x-jith F o r ste r's (1955) ob servation s near Dartmouth,

Devon. The v a r ia tio n in s iz e from p lan ts o f 3-4m found a t depths o f 5-6m 4 and th e undersized, deformed specimens recovered from 15“ 1?m i s em phasised. i

No such deform ity was seen in P h y llo g ig a s. John (1969) found th at th e I '’in d iv id u a l performance o f L. ochroleuca remained constant a t a l l depths and ■

the low production at depth i s explained in terms o f a red u ction in th e d e n sity j o f in d iv id u a ls rather than in d iv id u a l performance. Kain (1971&) c o r r e la te s

t h is reduction in d en sity at depth wdth reduced lig h t a t the time o f ; e s t abl i sliment *

The biomass data presented in Table 6.1 show th a t the o v e r a ll

|)r o d u c tiv it5'‘ o f the area stu d ied i s low compared m th other s i t e s. MacFarlane | ( 1952) compared her data m th the average S co ttish v a lu e s o f 5 to 8kg. fresh : xveight (Walker, 1954 ) and a ttrib u ted the higher p r o d u c tiv itie s in Nova S co tia - to th e greater t id a l exchange in th ose xvaters. However, the data of Jupp (19?2) ! i s in c lo s e r agreement. Luning ( 1969b) found standing crops of 11 d k g. fresh

^2 —2

weight ra at 2.0m and only 0.1k g. fresh weight.m a t 5°5m for a L. hyperborea :

fo r e s t in Helgoland*

The figu re o f 4*5 for LA.I of P h yllogigas i s in clo se agreement wdth ‘

most s.rable crops and 6 to 11 fo r grass and fodder crop s. Luning ( 1969b) quotes valu es of 4*1 and 1.6 at 3»3m in a L. liyporborea fo r e s t in Helgoland*

The in crea se in plant lo n g ev ity in more northern la titu d e s has been in d ica ted by Kain (196?) as the main reason for the larger p la n ts found in th ese la titu d e s ; the same reason may be ap p licab le to the large p la n ts found in high southern la titu d e s also*

The stru ctu re o f the L* liyuerborea fo r e s t in d ic a te s th a t shading e f f e c t s and fa c to r s a ffe c tin g the m o rta lity o f older p la n ts are found

(Kain, 1963; Jupp, 1972)» Fliy llo g ig as was often seen to ex liib it se lf-sh a d in g and Xfith laminae ly in g c o ile d up on the substratum , (see F ro n tisp iece)*

No c o r r e la tio n can be made between ch lorop h yll content and depth -o f Ph y llo gigas* Drew (197T) found the chlorophyll content of young laminae

to be 27*8 tig Chlocm*"'' and 32.0 ug Chi.cm"' in old fronds which agrees c lo s e ly with h is (unpublished) data fo r L. hyperborea of 21*7 and 30*8 ug Chlocm”"'*

2 1

The value obtained for SLA varied between 0.06 and 0*088 cm .mg"

—1