to the south as they approach the east coast of the North Island. Here warm water from the Tasman was not in evidence during 1949, suggesting that the East Australian Current turned back on itself and continued north in an anticlockwise direction to rejoin the parent current.

The Hauraki Gulf lies between the February and August sea isotherms of 20.0 and 13.3–14.4° C. The average annual range therefore does not exceed 6.7° C. The following figures (from unpublished records at the Geophysical Observatory, Wellington) have been averaged from surface temperature data collected by coastal vessels between 36 and 37° S.

These figures are considered to be fairly representative, but the margin of error must be considerable since when spot readings are made, no account is

Text-fig. 6.
Monthly average sea surface temperatures. 1935–1938 Auckland Harbour — — Coromandel Harbour…………

taken of time of day, and local variation in such factors as cloud, sunshine and wind.

Detailed records for waters in the Gulf have not been assembled previously in any systematic form of monthly averages. Under the direction of the late W. M. Jones (Geophysical Observatory, Wellington) a survey has been made recently of surface and deep water temperatures. These figures are not available for security reasons. A set of published figures appears in a Marine Department report on Fisheries (1938, p. 40) tabulated from the 4-year period 1935–1938. The graphs in Figure 6 illustrate the essential similarity between monthly averages for Auckland and Coromandel Harbours.

A number of inshore records were made by the writer in a depth of 0.5 to 1.0 metre at Clifton Beach, north of Narrow Neck (Table III). These were not made at frequent enough intervals to be of much value, although they serve to indicate sudden drops between May and June, after which months records remained consistently low until mid-September. Making no allowance for local weather changes, highest sea temperatures occurred between 3.00 and 5.00 p.m.

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Much work remains to be done on the problem daily, monthly, and annual temperature variation in the Hauraki Gulf. From the meagre records available, the lowest sea temperature was 12.2° C. (Clifton Beach, 20.6.49) and the highest 23.5° C. (Narrow Neck, 23.1.50). These figures probably do not represent absolute minima and maxima.

Of considerable significance in the intertidal region is the more extreme heating and cooling of exposed rock and shallow pools subject to strong illumination. The highest pool temperature so far recorded in the Gulf is 32° C., in a small, high level pool at Narrow Neck (Ambler and Chapman, 1950, Fig. 8). An abnormally high maximum of 38° C. was noted on exposed high-water boulders at Little Barrier (Station 24) on October 23, 1949. This was more than twice the corresponding sea temperature, which was only 17.8° C. On the same day at an exceptionally low spring tide the temperature among holdfasts of Ulva, Glossophora, Carpophyllum, Myriogramme and Plocamium was 29.1° C. The plants were dying; some were rotten, emitting the characteristic smell of decaying weed