4. Sub- (Infra-) littoral Fringe
Whichever prefix is preferred (“sub-” is chosen here for the sake of its widespread usage), the sector of the sublittoral proper to which the term applies is without doubt a natural and clearly defined one. Perhaps the most physiognomic feature of the Gulf rocky shores between M.L.W.M. and E.L.W. S.(approx.) is the dominance of Carpophyllum spp., less often replaced by Cystophora, Sargassum, Ecklonia, and rarely Lessonia. Womersley and Edmonds (loc. cit.) state that the fringe does not exist in its own right on Kangaroo Island, since it is merely an upward extension of a more or less uniform, upper sublittoral. Nevertheless they admit that Cystophora intermedia dominates an exposed belt which continues downward for only a limited distance (2 or 3 feet) Until more information is assembled from the sublittoral proper it is considered by the writer undesirable todogmatise about any further subdivisions. It may be noted, however, that there is a definite restriction on downward colonisation of dense belts of Cystophora torulosa, Carpophyllum maschalocarpum and C. elongatum whenever these occur in the sublittoral fringe. C. plumosum is an exception, for it is known to grow in submerged “forests” up to 4 fathoms below E.L.W.S. at Little Barrier (Station 24).
The validity of the sublittoral fringe concept may be affected by the degree of encroachment of large brown algae from the sublittoral proper. Information supplied in Table VIII, Part III,* indicates that none of the characteristic fringe species except Cystophora torulosa and possibly Carpophyllum elongatum (?) is confined to tide levels above E.L.W.S. This fact could be used to support Womersley and Edmonds' argument that there is no such zone as a sublittoral fringe. On the other hand the following facts seem to the present writer to support the view that the fringe has a valid entity and belongs, strictly speaking, to the littoral (in Stephenson's sense (1949, p. 200), i.e., from about E.H.W.S. to E.L.W.S.):
the presence of dominant brown algae, whatever their entire ecological range, in regular horizontal bands, made up of more or less uniformly dense aggregations of individuals;
the frequent modification in growth form of the components, chiefly by their stunted length in comparison with continuously submerged thalli;
the change in nature and effect of the governing environmental factors. Chapman and Trevarthen have drawn attention to the probable limiting effects of continuous emergence on upward extension of sublittoral species, and of continuous submergence on downward spread of littoral groups. Added to these is the mechanical and aerating action of breaking waves.
[Footnote] * Table VIII, Part III: Records of sublittoral brown algae in the Hauraki Gulf.