Little Papanui is placed on the tip of Otago Peninsula, jutting out towards the nearby continental shelf and into the South Pacific Ocean (Text-fig. 1). It is thus well exposed to continuous wave action, whether wind is blowing or not. The continuously surging and breaking Pacific rollers are the chief ecological feature whereby this shore differs from the harbour shore previously considered.
In climatic features the two regions, only five miles apart, probably differ but slightly. In a general way, the sunshine and rainfall data given in the previous paper may be applied here; i.e., hours of sunshine per month would probably usually lie between 80 and 200, and rainfall would average about 30in a year, fairly evenly distributed through the months. Total wind experienced at any given part of Little Papanui per year is probably less than at the tip of Aquarium Point by the marine station; for the latter is exposed to both southerlies and northerlies. At Little Papanui, on the other hand, cliffs cause local protection.
Southerly winds are more often of gale force than northerhes, so that on the whole the north end of the beach is exposed to greater wave action.
Little Papanui itself consists of a half-mile stretch of sandy beach bounded by high cliffs at each end.The cliffs at the north end (Fig. 2), about 80ft in height, have large boulders at their base intertidally nearest the beach, a sloping wave-cut platform east of this and further seawards drop vertically into the water. The height and aspect of the cliffs keeps the shore below in continuous shade during the winter months, and shaded till middle day in summer. Fresh water seepage occurs at several points.
The south end cliffs (Fig. 1, Text-fig. 2) are sun-facing, and jut out to shelter rocks below from southerly storms.A tiny offshore islet further helps break wave force. Hence the boulders and rocks intertidally here are not exposed to nearly such strong wave action as at the north end of the beach.
For the rest, a rocky reef (the Northern Reef) runs out to below low tide near the north end of the beach, South of this, rocks are exposed along much of the beach during periods of sand depletion (Fig. 1), but at other times the sandy beach is continuous except for a cluster of boulders above half tide. Areas of unstable stones occur by these boulders, adjacent to the Northern Reef, and at the inner corner of the south end (Text-fig. 2, small dots). The relatively lifeless habitats of unstable stones and unstable sand are not considered in this paper.
The rock of the rocky shore is predominantly coarse basalt, hard and of dark colour.
The region lies in the cold temperate zone, nearly always south of the subtropical convergence. Ice does not occur in open sea here. There are probably occasional frosts intertidally, although none were observed during visits.
Inshore surface sea temperatures have been recorded approximately weekly from the cliffs below Cape Saunders Lighthouse, about two miles south of Little Papanui. Monthly averages of these are plotted in Text-fig. 3, continuous line; while the broken line shows sea temperatures at Aquarium Point, averaged for the same dates. As might be expected, the outer coast sea temperatures neither rise as high in summer nor fall as low in winter as those of shallow, land-locked Otago Harbour. Of individual sea readings from Cape Saunders, the minimum in 1954 was 84° C. on 10.7.54, in 1955 was 7.9° C. on 16.7.55; the maximum in the summer of 1954–5 was 14.9° C. on 22.1.55, and the following year was 16.2° C. on 27.1.56. Scattered inshore sea temperature readings were taken at Little Papanui during field work. These, shown as squares and circles on Text-fig. 3, are in fairly close agreement with the more regular Cape Saunders readings Of 95 Cape Saunders readings nearly weekly over two years, 93 lay between 8.0° C. and 16.0° C. The high sea and harbour temperatures of early 1956 were associated with a heat wave, of air temperatures exceptional for the region.
Tides are semi-diurnal, low spring tides occurring about 1¼ hours earlier than predicted for the Port of Dunedin. Tidal range was measured, as closely as was practicable, by a temporary scale on a calm day at the less wave-exposed south end of the beach. On 5.9.56, with a predicted low spring tide for Dunedin of minus 0.3ft (the lowest predicted for 1956) and barometer at 30.2ins, high tide level.
Text-fig. 3.—Surface tea temperatures Heavy line, monthly averages of approx. weekly 9 a.m. readings taken below Cape Saunders Lighthouse, near Little Papanui.Broken line, monthly averages of 9 a.m. temperatures on same dates taken from end of main wharf at Portobello Marine Station.Months during which points based on fewer than 3 readings marked with asterisk. Scattered individual low tide sea readings during field work at Little Papanui marked as squares (1953 and early 1954) or circles (mid-1954 to 1956).
was between 7½ft and 8ft above low tide level, as marked on Text-fig. 4. In general, on most of this shore where Pacific rollers continuously break, precise tidal levels are not easily defined. In practice, low spring tide level is regarded as the level readily accessible on a low spring tide, and other levels are gauged upwards from this and from coverage at different times of tide.