REPRODUCTION IN THE SEAGRASS ZOSTERA-NOVAZELANDICA ON INTERTIDAL PLATFORMS IN SOUTHERN NEW-ZEALAND

This study investigates the reproductive periodicity and reproductive output of the seagrass Zostera novazelandica on two intertidal reefs. Peak numbers of flowering shoots occurred during March (late summer) o f two years at both sites and no flowering shoots occurred during the winter months of July to September. There were greater numbers of flow ering shoots in seagrass patches in the low intertidal zone (up to an average of 55 per 0.1 m(2)) compared to the middle (up to 20 per 0.1 m (2)) and upper (up to 9 per 0.1 m(2)) zones, and about three times gre ater reproductive output in patches associated with tidepools compared to those not bordering tidepools. The average number of inflorescence s per shoot was 3.1 (+/- 0.25) at one site vs 1.2 (+/- 0.08) at the ot her, and showed a progressive decrease from the lower shore to the upp er shore. Patches associated with tidepools had twice the number of in florescences per shoot(2.8 +/- 0.24) than patches not bordering tidepo ols (1.5 +/- 0.16). The number of flowering shoots was highly correlat ed with leaf width, leaf length, and ramet density, while the leaf-are a index decreased from the lower shore to the upper shore. The reprodu ctive effort of plants, as measured by the percent biomass invested in flowering shoots during peak reproduction, was significantly differen t between sites, tidepool associations, and shore level. For all the v ariables measured, there was considerable spatial variation, with sign ificant interaction terms between most factors investigated. In labora tory experiments, more inflorescences were produced at light intensiti es of 30 and 300 mu E m(-2) s(-1) than at 100 mu E m(-2) s(-1). At a s alinity of 17 parts per thousand, 1.5 x the number of flowers was prod uced than at 33 parts per thousand, while none was formed at 70 parts per thousand. Plants cultured at 5 degrees C had about three times the number of inflorescences than those at 15 degrees C, while none was f ormed at 25 degrees C.