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1. Supralittoral Zone
According to the locality, the supralittoral zone may be completely devoid of colonists, or it may be quite obscured by a continuous cover. On most Waitemata Sandstone cliffs the zone is bare (contrast however, Fig. 7) owing chiefly to the rapid erosion of the soft, crumbly strata and hence to the initial difficulty for any plants of securing a firm attachment. Added to this the generally porous nature of the cliffs does not aid in moisture conservation, except in places where there may be a seepage or trickle of fresh water from above.
At several stations, the most striking being those on Little Barrier, naked cliffs are partially or entirely clothed by a canopy of Metrosideros excelsa, which thrives within reach of salt spray. Where its branches overarch upper midlittoral rocks, as at Station 32 (Port Fitzroy) shading effects are reflected in local variations superimposed upon the general zonation pattern. Phormidium and Bostrychia may find refuge in depressions on its shaded branches.
Other angiosperms frequently encountered are Mesembryanthemum australe. Coprosma repens, Salicornia australis and Stipa teretifolia (Cf. Carnahan, 1952, p. 39). The most striking feature of the supralittoral in most other districts is the conspicuous cover of grey, and sometimes also yellow, lichens. The grey lichens (Ramalina, Physcia, Parmelia spp.) range upwards from a lower limit of about 2 to 50 feet above E.H.W.S. The density of cover varies according to degree of cohesion of the cliff surface (Cf. Fischer-Piette, 1936, p. 219). Xanthoria parietina generally occupies the band below, which may be included in the supralittoral fringe. This assemblage is a distinguishing mark in many places
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inside the Gulf, in particular about the shores of Waiheke and smaller islands (e.g., Shag Rock, Plate 4, Fig. 1), and on bare cliff faces on west Coromandel Peninsula. But the grey lichen community is by no means restricted to relatively homogeneous, unbroken surfaces. At Whangaparapara (Station 31) and Little Barrier for instance, where the surface is made up of slab-like or rounded pebbles and boulders, foliose Physcia and Parmelia and tufted Ramalina abound. However, cohesion of the surface is still an important factor at these stations, for although the actual surface layer is irregular and dissected, the boulder faces are weathered to a smooth, firm, closely-compacted consistency.
The occurrence of littorinids (Melaraphe spp.) in the supralittoral zone is confined to stations with a wave exposure index of McW2–4D2, Ta2 (Cf. Stations 28, 33); in other words, an exposed coast, fairly deep-water locality. Similar reports come from Piha (Beveridge and Chapman, 1950, p. 190). But in the majority of places where Melaraphe abounds in the Hauraki Gulf it seldom ventures above the upper extremity of the supralittoral fringe.
Outliers from the fringe may include Verrucaria, Hildenbrandtia and Lichina. Figure 9 illustrates what a small percentage of the space available is actually occupied by these forms, which, at 5 or 6 feet above normal tide levels, are driven into sheltering cracks and crannies, and their presence is discovered only by an intensive search.
While the supralittoral zone as a whole is of secondary consideration in the present survey, the prominence of the grey and yellow lichen belts in moderately sheltered parts of the Gulf is without doubt one of its physiognomic features. The uppermost limit of the belt does not concern us here, but is frequently regulated by the undulating, lower limit of soil (adlittoral) vegetation. The lowest limit is bounded by a sudden increase in black tufts of Lichina, where it is present, or by a naked expanse of rock if it is sparse or absent.
Local development of Prasiola stipitata (Station 22) in a fairly exposed habitat associated with gannet droppings may be compared with Womersley's (1948, p. 149) report of a similar community on the site of well-worn penguin tracks at Pennington Bay, Kangaroo Island.