Dataset: Seagrass surveys in Exmouth Gulf, Western Australia


In September 1994, seagrass surveys were undertaken at 64 sites in Exmouth Gulf. Sites were grouped into 5 areas located along the eastern and southern coast of Exmouth Gulf and 1 area on the west coast.

Initially, spot checks were used to describe the type and extent of the benthic vegetation. If seagrass was not seen, the sediment was also checked for the presence of rhizomes. Areas where seagrass was present in measureable amounts were selected for quantitative sampling. Water depth and substrate composition were also recorded.

Percent cover of seagrasses (by genera, or species when easily identified) and algae (in functional groups) was estimated from 5 replicate quadrats placed randomly on 50m, haphazardly laid transects. For each quadrat, taxa were identified under 100 points on a 1m² string grid.

The density of seagrasses and any abundant macro-invertebrates was also recorded within 5 replicate 50cm² or 25cm² quadrats randomly placed on each transect. Seagrass density was determined by counting the numbers of erect shoots (leaf groups/clusters) per quadrat.

At 3 sites, 2 transects separated by 100 to 200m were sampled to examine patchiness in seagrass abundance at that scale. At 5 sites, all plant matter in 50cm² quadrats was collected and frozen for biomass estimates. The thawed samples were blotted, separated into above ground and below ground fractions and the wet weight measured.

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