ii. Tide Levels

In any water mass partly enclosed by land considerable variations in both time and height of the tide may be expected to occur. Many workers on intertidal ecology have found from experience that, owing to a frequent deviation of tidal behaviour from the normal for the nearest port of reference, each locality needs to be studied on its own. In the Hauraki Gulf extreme spring tides range from about 14. Oft. in Coromandel Harbour to about 8 Oft. at Cuvier Island. Taking Auckland as the standard port of reference, the following figures taken from the Nautical Almanac (1950) give the ratio of the tide ranges for localities where it is known:

The writer's brief observations of tidal behaviour in the Gulf (Table V) varied from that made over a weekly period (Station 24) to those over a single 6-hourly rise or fall of the tide (Stations 17, 30, 32).

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In the above table the Coromandel Harbour figures are obviously not applicable to Long Beach, which is only 5 miles away, but is situated on the open coast. Results from Ti Titoki Flat, Little Barrier, also appear anomalous in comparison with the expected ranges at Tryphena. The neap range is greater but the spring range is smaller, if splash is not taken into account. The splash zone (Colman, 1933) was particularly hard to estimate here owing to the broken surface topography occasioned by the loose stones and boulders. Figures from Fletchers Bay agree substantially with the expected record for Cuvier Island; likewise Whitianga with Mercury Bay. and Arran with Auckland. The range at Port Fitzroy appears on superficial examination to be slightly less than at Tryphena,