The standing stock, growth and shoot production of Zostera capricorni aschers. in Botany Bay, New South Wales, Australia

Abstract

Zostera capricorni Aschers. occurs at many shallow sites in Botany Bay, with the exception of one 5-km section of exposed sandy beach; however, bed distribution is very patchy. Details are given for shoot and underground biomass (g fresh weight), shoot density, leaf length and leaf width at 20 representative sites around the Bay. Z. capricorni was found to grow best between −0.2 and −1.0 m, with a lower limit between −2.0 m (northern side) and −3.2 m (southern side). The mean percentage cover was determined for six large areas in the bay. Shoot biomass (g dry weight) was found to be logarithmically related to percentage cover, whereas shoot density (numbers m −2) was linearly related to percentage cover. Large seasonal changes occurred, with a winter die-back characterised by a 4-fold reduction in shoot biomass and a 2-fold reduction in shoot numbers. Flowering occurred from September to April. An equation is presented for determining the total above-ground stock for an area. The total summer above-ground stock of the bay was estimated at 18 ± 8.1 tonnes for a total area of beds of 309 ha. Mean annual leaf production was estimated to be 5.22 ± 0.52 gDW m −2 day −1 for a representative healthy bed at 0.3 m depth, and leaf plus flower production was 5.86 ± 0.59 gDW m −2 day −1. The total above-ground production for all the beds of the bay was estimated to be 512.7 ± 51.3 tonnes year −1, i.e. 1.66 ± 0.17 tonnes ha −1 year −1.