Competition between subspecies of the mangrove Ceriops tagal along a salinity gradient in north Queensland

The distribution of seedlings of the two subspecies of Ceriops tagal (Ceriops tagal var. tagal and Ceriops tagal var. australis) was measured in relation to soil pore water salinity in the "Wet Desert" in Missionary Bay on Hinchinbrook Island and at Chunda Bay. At each location, three 60 m transects, spaced 10 m apart, running from the interface between the terrestrial and mangrove forests into the mangroves were established. Three replicate soil cores were taken at 10 m intervals along each transect and the salinity of pore water draining into each hole was measured using a conductivity meter. If water did not percolate into the hole, soil samples were taken to the laboratory and squeezed under low pressure to obtain a pore water sample. The density of seedlings of both subspecies was also measured in 3 replicate 10 m² quadrats at each 10m interval along each transect.Freshly picked, mature hypocotyls were weighed and planted out in trays in a shadehouse in different combinations of salinity and proportion of each subspecies. The salinities used were 0, 15, 30, 45 and 60 ppt, while the proportions of subspecies were 100% of a given subspecies, 67% tagal-33% australis and 33% tagal-67% australis. Stem height, percent mortality and percent leaf emergence were measured every week for six weeks and every 2 weeks for a further 4 months. This research was undertaken to determine if competition between the two subspecies of Ceriops tagal contributed to the difference in the distribution of the two subspecies along a salinity gradient.