THE DISTRIBUTION OF PADINA PAVONICA 57 



Some of the available reports could have been derived from drift material, even when not so 

 acknowledged. Despite our own observations on the rarity of detached drift material being thrown 

 up on British shores, there are 18th and 19th century reports of drift specimens, attached to small 

 stones, pebbles, or fragments of rock, thrown up on the shores, especially of Belgium and 

 Netherlands but also in some parts of England (see Pulteney, 1799; Pulteney [& Rackett], 1813). 

 Since most of these reports are more or less contemporary with the unusual British records 

 examined here and both are often the only basis for subsequent acceptance of Padina in the local 

 flora, there must be reservation as to the part played by drift. Padina populations may (although 

 there is no evidence for it) have been then much larger in adjacent more favourable areas, giving 

 rise to greater amounts of drift, detached or still attached to fragments. Seoane-Camba (1965), for 

 example, has recently recorded drift material of Padina at Barbate (Cadiz), an area where many 

 populations are known. It remains unlikely that drift material could be the explanation behind the 

 observations made on British coasts by Hill (Sussex) or by Smith, Sowerby, & Johnson (Sussex; 

 Kent), much less of the precise data recorded by Turner (about the Leathes Margate record), by 

 Wood (Kent), or by Dale in Taylor and Dale (Essex). 



Variations between Britain and the adjacent continent 



The apparent general absence, with the poorly-authenticated exceptions indicated earlier, of 

 Padina from Cornwall is curious and anomalous. The situation in Brittany, the French analogue 

 of Cornwall as to position and marine physical environment, emphasises still further the strange 

 absence from the far west Channel coasts. Distribution of P. pavonica in Brittany is by no means 

 continuous along the coasts; in view of its moderately strict habitat requirements, the alga could 

 not be expected to appear everywhere there. However, there are long stretches on the north coast 

 (between Locquemeau and Conquet) where conditions are apparently suitable (e.g. as at Roscoff) 

 but in which Padina is rarely if ever recorded. Generally elsewhere in Brittany, plants are locally 

 and seasonally very evident. The whole county of Cornwall, by contrast, with many suitable 

 areas of substrate, shelter from wave-action, and adequate temperature regime, seems now to lack 

 populations with any longevity. We have no good modern evidence that even sporadic individual 

 plants appear there. If they are confirmed by intensive surveys, these distributional blanks will re- 

 emphasise the strong likelihood that breeding populations and established vegetative populations 

 of some so far unknown minimum size are necessary if the alga is consistently to appear, even in 

 otherwise suitable circumstances, towards the northern limits of its eastern Atlantic distribution. 



There is an apparently strong resemblance between the general form of the distribution on 

 British southern coasts and that on the northern French Atlantic coasts, the latter including the 

 Channel Islands. Since there is considerable correspondence in substrata and their distribution on 

 the two sides of the Channel, as well as similarities in other aspects of the physical environment, 

 this is not surprising. The Channel coasts of France are not so much nearer to the present distribu- 

 tion centres of Padina that significant variations attributable to behavioural differences, environ- 

 mentally or internally determined, are likely. 'Foci' in the Padina distribution pattern on French 

 shores of the English Channel are therefore to be expected, of which the similarities in distribution 

 on both sides of the Channel are principally a reflection. 



There appear from available information to be no tremendous or sudden changes in the bio- 

 logical characteristics shown by Padina pavonica in the different areas and populations to be found 

 between Brittany in the north and Cadiz in the south, although the general trends are not always 

 absolutely maintained at local level. There is no apparent change in substrate or other habitat 

 requirement along the whole north-east Atlantic coastline from Great Britain southward to 

 Algeciras. Temperature and insolation with depths, and hence the overall depths within which the 

 levels of these are tolerated by Padina, clearly vary between Britain (where there has never been an 

 authenticable record deeper than the immediate metre depth of the infralittoral fringe level) and 

 the Mediterranean (whence valid records from considerable depths have already been indicated 

 earlier). Temperature is probably the principal constraint in this, although the sequence of change 

 may be misrepresented due to lack of information. There could, for example, be plants in greater 

 depth than so far recorded for the infralittoral along Atlantic mainland (e.g. Portuguese and 

 southern Spanish) coasts. Further information is required on both this and the following points. 



