A d e ta ile d survey of the shallow s it e and i t s immediate v ic in it y was /carried out fo r a- number o f reasons;
'1* To determine the abundance and d istr ib u tio n of the flo r a in r e la tio n to the topography and su bstrate
2. To see i f any zonation o f the major a lg a l groups - e x iste d
3* To gain an id ea (w ith subsequent lamina, area measurements o f th e biomass o f P h y llo gig as in th at area
4» To gain some exp erience o f underwater mapping tech n iq u es. ■
Mapping was ca rried out over the period 24*10.74 to 29.11.74$ tak in g f u l l advantage o f the e x c e lle n t v i s i b i l i t y found w ith the presence o f sea—ic e. ‘ The break-out o f the ic e w hile s t i l l some 20cm th ick on 30. 10.74 in terrup ted the work and some p o in ts were rechecked in e a r ly 'tranuary when the phytoplankton bloom was on the d e c lin e. The f in a l area
surveyed was 25m x 40m. . ,
i n i t i a l l y à 40m base lin e was la id along th e sand/rock boundary on the cove flo,or,'.|tt, approxim ately 7m ( 24*) depth. This lin e , th in , orange polypropylene cord was Icnotted every 2m and marked with a p iece o f w hite tape every 10m, and i t s ends anchored w ith 41b lead w eig h ts. At each end,
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lin es were la id a t r ig h t-a n g le s running up to the c l i f f face and marked as before every 2 and 10m (see P ig. 3 .4 )*
■a
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a #The corner angle was determined using' a r ig h t—angle made o f two 9 ft lengths o f dexion angle ir o n , b o lted to geth er on the bottom. ^ ith th e e xc e lle n t v i s i b i l i t y th ere were no problems in lin in g up th e
ropes c o r r e c tly. Three secondary lin e s were la id p a r a lle l to the base lin e and th e s e , marked as b efo re, formed 2m squares which were in d iv id u a lly mapped. D ivers engaged in mapping carried a s e t of form ica boards marked out -with a 4cm square g r id. D ifferen t coloured ’Chinagraph® p e n c ils were
used to in d ica te ro ck s, a lg a e , e t c. (The fin a l sca le o f the map was 2cm s tm ). As an area was com pleted th e lin e s were leapfrogged up th e slope and the
p rocess repeated u n t il the c l i f f was reached. Other measurements, such as • g u lly width were determ ined w ith a 2m p o le.
A fter each dive th e work was tran sferred from th e mapping boards . ; to a m aster copy on the same s c a le. In divid u al p la n ts o f P h yllogigas and ' -?- Ascoseira were noted down and the D esm arestiales drawn in en masse w ith
oblique lin e s. The red a lg a e , m ainly Plocamium, covered a l l boulders below 2m an d ,fo r the sake o f c la r it y were excluded from the f in a l copy. A note on th e ir d is tr ib u tio n was included in th e Key.
Within th e area covered by the map, th e su rface areas o f laminae Qf"P h y llo g ig a s were measured by two d iv e r s. One d iver h eld a 1cm wide tape measure at th e base o f the lam ina, where i t v/as the same vjidth as the measure and the second d iv er la id the lamina out f la t and measured to the extreme t ip. Tha maximum width was a ls o n oted. A ll the laminae measured showed sign.s o f abrasion d is t a lly and along th e ir la te r a l m argins. .. /
This method o f measurement does not allow fo r any cunrature of the -lamina; i t i s assumed to be f l a t and regular whereas both la te r a l and h o rizo n ta l curving are p resen t. C orrections fo r t h is were ap p lied by re measuring in the lab oratory sev era l laminae p reviou sly measured underwater
and comparing the r e s u lt s. Two methods were used; ,
1o The o u tlin e s o f some o f the sm aller laminae were traced onto graph ' paper and th e squares counted,
2 , A laiown area o f lamina was weighed and compared w ith the to ta l lam ina fresh w eigh t. R ep lica tes were taken to allo w fo r the decrease in lamina w eight per u nit area away from the meristem at the base o f.th e frond.
These two methods agreed to w ithin 6/>; the f ie l d method gave r e s u lts 30^ la rg er than th e s e.