Method Of Investigation

The area under investigation was visited at least twice a month for a period of 18 months. On several occasions visits on consecutive days were made over periods of up to one week. This enabled observations to be made in all types of weather and under varying tidal conditions. The relation of the organisms selected to tidal levels was studied by the method used by Evans (1947). This method involves the direct observation of tidal heights, the results obtained by Evans showing a high degree of accuracy, providing the observations are made on a calm day and the levels checked on different days and at different states of the tide (springs and neaps).

Starting from the high water mark, the area studied was traversed horizontally, along the water line, every half-hour during the first, and last 90 minutes, and every quarter hour during the middle of the ebb tide. Notes as to the presence and absence, abundance and distribution of the various species were made during each traverse. The tidal data were obtained from records of the Lyttelton Harbour tide gauge, and the height of each traverse was calculated from the” New Zealand Nautical Almanac” (p. 110). Actual measurements were also made on vertical faces.

The following species were selected for special study with reference to tidal level, exposure and submergence, exposure to wave action, rock configuration and relationship to other organisms.