Spatial variation in reproductive effort of a southern Australian seagrass.
In marine environments characterised by habitat-forming plants, the relative allocation of resources into vegetative growth and flowering is an important indicator of plant condition and hence ecosystem health. In addition, the production and abundance of seeds can give clues to local resilience. Flowering density, seed bank, biomass and epiphyte levels were recorded for the temperate seagrass Zostera nigricaulis in Port Phillip Bay, south east Australia at 14 sites chosen to represent several regions with different physicochemical conditions. Strong regional differences were found within the large bay. Spathe and seed density were very low in the north of the bay (3 sites), low in the centre of the bay (2 sites) intermediate in the Outer Geelong Arm (2 sites), high in Swan Bay (2 sites) and very high in the Inner Geelong Arm (3 sites). In the south (2 sites) seed density was low and spathe density was high. These regional patterns were largely consistent for the 5 sites sampled over the three year period. Timing of flowering was consistent across sites, occurring from August until December with peak production in October, except during the third year of monitoring when overall densities were lower and peaked in November. Seagrass biomass, epiphyte load, canopy height and stem density showed few consistent spatial and temporal patterns. Variation in spathe and seed density and morphology across Port Phillip Bay reflects varying environmental conditions and suggests that northern sites may be restricted in their ability to recover from disturbance through sexual reproduction. In contrast, sites in the west and south of the bay have greater potential to recover from disturbances due to a larger seed bank and these sites could act as source populations for sites where seed production is low.
School of Life and Environmental Science, Centre of Integrative Ecology, Deakin University, Waurn Ponds, VIC, 3217, Australia. Electronic address: tim.smith@deakin.edu.au.
Timothy M
TM
Smith
School of Life and Environmental Science, Centre of Integrative Ecology, Deakin University, Waurn Ponds, VIC, 3217, Australia; Centre for Tropical Water & Aquatic Ecosystem Research (TropWATER), James Cook University, Cairns, QLD, 4870, Australia; School of BioSciences, University of Melbourne, Parkville, VIC, 3010, Australia.
Paul H
PH
York
School of Life and Environmental Science, Centre of Integrative Ecology, Deakin University, Waurn Ponds, VIC, 3217, Australia; Plant Functional Biology and Climate Change Cluster (C3), School of the Environment, University of Technology Sydney, Broadway, NSW, 2007, Australia.
Peter I
PI
Macreadie
School of BioSciences, University of Melbourne, Parkville, VIC, 3010, Australia.
Michael J
MJ
Keough
Institute for Marine and Antarctic Studies, University of Tasmania, Taroona, TAS, 7053, Australia.
D Jeff
DJ
Ross
School of Life and Environmental Science, Centre of Integrative Ecology, Deakin University, Waurn Ponds, VIC, 3217, Australia.
Craig D H
CD
Sherman
D059001:Aquatic Organisms; D001315:Australia; D018533:Biomass; D017753:Ecosystem; D004777:Environment; D004784:Environmental Monitoring; D012098:Reproduction; D012639:Seeds; D035962:Zosteraceae / Q000502:physiology*
Flowering; Heterozostera tasmanica; Reproductive investment; Seagrass; Seed bank; Sexual reproduction; Vegetative growth