Peel-Harvey Estuary Macroalgae Data

Brief description

This dataset contains maps of macroalgal biomass and species compositions that were measured at 30-42 sites at least once a year between 1978 and 1994, except from 1980 to 1983. After the opening of the Dawesville Channel, seasonal (spring, summer and autumn) sampling of macroalgal biomass and species composition took place at 42 sites.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Data can be accessed on a CD-ROM available from the Murdoch library. Stratified macrophyte sampling was conducted at sites selected to best represent the environments in the System. At each site, five replicate cores were collected by divers using Perspex corers (9 cm diameter x 50 cm length, total area = 64 cm2). The cores were pushed into the sediment surface over the benthic macrophytes and sealed. Plant material was sieved to remove excess sediment and bagged for transport. At the laboratory each sample was sorted into species, oven dried at 70°C to constant weight. Dry weights were determined to 2 significant figures and biomass converted to grams per unit area gm-2. Estimates for species biomass are the means of five replicates. Total macrophyte biomass for an individual site could vary significantly; standard errors for particular sites were generally between 25 and 50% of the mean. The total biomass, along with the total macrophyte biomass in the Peel Inlet, of each macrophyte component, was estimated using a computer mapping system ("SYMAP", Dougenik and Sheehan, 1977)[Dougenik, J. A. and Sheehan, P. E., 1977, Symap Users Reference Manual, 5th edition, Laboratory for Computer Graphics and Spatial Analysis, Harvard University, Cambridge Mass.] which provided contours comprising different quantities of the biomass of a particular component. The method for estimating the biomass for the Inlet is therefore subject to the limitations of the SYMAP method. As there were relatively few sites sampled for such a large water body, this may lead to overestimates of biomass. Adherence to the same sampling sites and methods produced a valid representation of trends in biomass. To increase the accuracy of biomass estimates for Harvey Estuary, from 1994 onwards, visual transects were used to determine the extent of macroalgal and seagrass growth. These areas were multiplied by the macroalgal biomass at each site, then summed to give a figure for macroalgal biomass for the total area. This method was adopted because macroalgal populations in Harvey Estuary are of a far lesser magnitude and are more evenly distributed than in Peel Inlet. Areas of sites were determined by digitising a map of Harvey Estuary into a computer program, CanvasTM, to determine site areas. The one metre contour was used to divide the sites, as very little macroalgae is found beyond this depth.