Marine Algal Ecology of the Hauraki Gulf, New Zealand* This work was undertaken during the tenure of a University of New Zealand Research Fund Fellowship at Auckland University College Botany Department, in 1949 and 1950. By Vivienne Dellow† Now Mrs. R. M. Cassie. [Received by the Editor, July 30, 1954.] Summary Thirty-four stations in the vicinity of the Hauraki Gulf have been surveyed. In Part I, a discussion of the factors comprising geology, climate and hydrography, special attention is drawn to effects upon intertidal populations of substrate, air and sea temperatures, salinity, pollution, turbidity, tides, currents and wave action. Guiler's (1949) formula has been applied to each station in order to provide an index of the type of wave action. In general accordance with T. A. and Anne Stephenson's (1949) schema for universal zonation on rocky shores, this area can be subdivided into supralittoral, midlittoral and sub- (infra-) littoral zones. A distinct fringe of both supra- and sublittoral zones is recognizable at upper and lower boundaries of the mid-littoral. Part II concerns these divisions, and the groups of species they contain. Twenty-nine “permanent” and 11 seasonal communities are described, and 241 algae have been identified from the Gulf region. In Part III the major features of horizontal and vertical zonation are considered, with particular reference to the factors of substrate and wave action. Five representative vertical sequences are described and figured in detail, and then comparisons are made with reports from other North Island coasts. On the basis of Stephenson's (1947) temperature boundaries, the Hauraki Gulf is classified tentatively as warm temperate. The relative paucity in numbers of algal species is attributed in part to the degree of turbidity and organic pollution, especially in the approaches to the Auckland Harbour. Finally, basic vertical zonation sequences are given for the Gulf under conditions of moderate shelter and extreme wave exposure, and these are compared and contrasted with similar sequences on warm temperate rocky coasts in both Northern and Southern Hemispheres. Part I. Table of Contents Introduction 1 General: Area and Methods 1 Environmental Factors 4      1. Geology 4      2. Climate 6      3. Hydrography 9 Part II. Terminology 21 Biotic Communities 22 Part III. Discussion 40      A. Horizontal Zonation 40      B. Vertical Zonation 49           Relationships With Other North Island Stations 56      C. Comparison With Rocky Coasts Beyond New Zealand 59