Do the assemblages of benthic macroinvertebrates in nearshore waters of Western Australia vary among habitat types, zones and seasons?

Brief description

Benthic macroinvertebrates were sampled seasonally in the subtidal and upper and lower swash zones at two sites in each of six nearshore habitat types on the lower west coast of Australia in summer and spring of 2000. The habitat types, were distinguished quantitatively using values for a suite of seven statistically selected enduring environmental characteristics

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Sampling was undertaken during daylight in each season between the summer and spring of 2000. Each site was sampled twice at a two to three week interval in the middle of each season to reduce the chances of the resultant data being unduly affected by an atypical sample (Morrisey et al., 1992). Five randomly-located sediment cores were collected in each season from each of the three zones at both sites in each of the six habitat types. The cylindrical corer was 11cm in diameter, covered a surface area of 96 cm2 and sampled to a depth of 15 cm. The samples were preserved in 5% formalin buffered in seawater and wet-sieved through 500-um mesh. Invertebrates retained on the mesh were removed from any remaining sediment using a dissecting microscope, identified to the lowest possible taxon and stored in 70% ethanol. The number of individuals of each macroinvertebrate taxon in each replicate sample was converted to a density, i.e. number of individuals 0.1m-2. The non-enduring environmental characteristics measured at each site in each season were water temperature, volume of any detached macrophytes on the beachface, sediment grain-size, contribution of particulate organic matter (POM) to that sediment and the depth of the redox discontinuity layer (i.e. the point at which the interstitial spaces in the sediment become depleted of oxygen). At each site on each sampling occasion, three replicate water temperatures (C) were recorded in the middle of the water column (i.e. in Zone C) and the volume of detached macrophytes, accumulated between the sand dunes and seaward limit of the swash zone, was measured along a 50m transect running parallel to the shoreline. Sediment grain-size and the contribution of POM to the sediment in three randomly-located cores of sediment (3 cm diameter x 15 cm high) collected in each of the three zones at each site on each sampling occasion were determined. The depth of the redox discontinuity layer in each core was then recorded to the nearest 1mm. The contents of each core were wet-sieved through nested meshes of 2000, 1000, 500, 250, 125 and 63 mm, with any sediment grains 563 mm being collected in a base pan. The fraction of sediment retained on each mesh was dried at 80 C for 24 h and weighed, thereby enabling the percentage contributions of each grain-size fraction to each core sample to be calculated. Each sieve-fraction was then ashed at 550 C for 2 h and reweighed to the nearest 1mg. The sum of the ashed sediment weights was subtracted from the sum of the dried sediment weights in each core sample to determine the percentage contribution of POM in that sample (Heiri et al., 2000).

Notes

Credit
Centre for Fish and Fisheries Research, Murdoch University

Credit
Strategic Research Fund for the Marine Environment (SRFME)