Seasonal changes in biomass and shoot characteristics of a Zostera capricorni Aschers. Dominant meadow in Cairns Harbour, northern Queensland

Abstract

Spatial and temporal variability of Z. capricorni biomass, shoot characteristics (canopy height, surface area, flowering), distribution and detrital content were examined from December 1988 to December 1990. Between August 1987 and August 1991, 15% (2.0 ha) of the meadow was lost. Biomass of above- and below-ground structures showed a unimodal seasonal pattern with maxima in late spring (mean 194.92 g dry weight m^-2 and 426.67 g DW m^-2 respectively) and minima in winter (mean 28.72 g DW m^-2 and 56.98 g DW m^-2 respectively). Mean above-ground biomass (95.53 ± 2.21 g DW m^-2) was approximately half the mean below-ground biomass (177.28 ± 4.49 g DW m^-2). Leaf canopy heights were greatest between October and February (maximum 53.4 cm) and lowest around mid year (minimum 4.4 cm). Leaf surface area per square metre of seagrass meadow ranged from 10.28 to 1.39 m² (mean 3,692 ± 0.104 m²), and flowering occurred during September and October. Detrital biomass ranged from 339.73g DW m^-2 to 11.83 g DW m^-2 (mean 77.39 ± 2.36 g DW m^-2). Detrital biomass was higher during July-October and lower during February-May. The climate during the study was typical for the area, and all trials displayed similar seasonal patterns, although the amplitudes differed among some trials. The environmental parameters that may influence seagrass and detrital biomass were investigated. The best models explained only 14% of the variation in above-ground biomass, 15% of the variation in below-ground biomass, and 21% of the variation in detrital biomass. These models suggest that fluctuations in seagrass and detrital biomass in Cairns Harbour were influenced by changes in light availability, temperature, salinity and exposure.