Health and Status of Seagrass in Cockburn Sound, Owen Anchorage and Warnbro Sound: 1998 to 2008

Brief description

Since 1998, a survey of seagrass health has been repeated annually between Stragglers Rocks and Warnbro Sound in the Perth metropolitan waters, in January, on behalf of DEC (Department of Environment and Conservation) and CSMC (Cockburn Sound Management Council). The survey has incorporated measurements of several quantitative variables at each assessment site, and also established a series of permanent transects over the lower depth limit of seagrass meadows at four different sites. Parameters measured (some were measured only in some years) include: - Seagrass shoot density - Shoot height (maximum) - Shoot height (average) - Leaf productivity - Seagrass above ground biomass - Epiphyte biomass - Photoquadrats - Photography of leaves - Video transect - Videography of leaves - Canopy cover (%) - Meadow cover (%) - Epiphyte cover (%) - Epiphyte composition - Rhizome mat - Coloniser species

Lineage

Maintenance and Update Frequency: annually

Statement: (all methodology complies with Standard Operating Procedures for the EPP (Cockburn Sound)) SEAGRASS HEALTH SITES *Qualitative data* Percentage cover - Estimation of cover within 20 x 20 cm quadrats, with shoots erect, looking from top of canopy. Epiphyte coverage - Visual observation of epiphyte composition (encrusting, filamentous, fleshy algal types) taken with close up video Presence or absence of dead rhizome material - At meadow periphery or in bare sand patches adjacent to seagrass, remove sediment to below the depth of present seagrass growth and examine nature and species of any dead rhizome Presence of coloniser species - Note if any coloniser species such as Halophila ovalis and Zostera tasmanica are present *Quantitative data* Permanent quadrats - At all sites, first locate the central star picket, then find the 4 transects. - To locate the transects (3 or 4) which originate from these six star pickets follow the bearings and distances indicated in Table 9.1. The star pickets marking the transects are labelled with plastic tags (e.g. 1S 1E = transect 1 start and transect 1 end). Attach a tape measure along the transect to locate the permanent quadrats at specific distances along the transect, indicated in Table 9.1. - Once the permanent quadrat is found, place the purpose made stainless steel quadrat over the permanent markers and conduct shoot counts, height measurements and canopy cover estimates. Videography - At all Seagrass Health sites, Reference sites & Depth Limit Transect sites videography is taken along the right hand side of the three to four transects when heading away from the central star picket, or down the depth gradient. - Close up videography of seagrass shoots noting epiphyte coverage, detritus beneath the canopy and any other factors of note such as rhizome mat or coloniser species. - No circular transects were taken in 2006. At all sites except Fish Rocks and Straggler's Rocks video was taken with a digital video camera and video from sites saved as independent mpgs. Within each site the different transects, epiphytes & rhizome mat & detritus were also saved as separate mpgs. At Fish Rock's and Straggler's Rocks video was saved on a video camera and the timing for each site & transect is indicated in Appendix 12. Shoot density - Count shoots in 20 x 20cm quadrats x 24 or 30 replicates at each site (see 'Permanent quadrats' section, above, for placement) - It is imperative that shoots are counted and not leaves. Shoots may contain between one and three leaves. Train any new workers and stress the need for accuracy in shoot density counts. Shoot height - Measure maximum shoot height in each of the above quadrats - From 2004 average shoot was measured in each quadrat. This involves estimating the height of 80% of the leaves above the sediment. DEPTH LIMIT TRANSECTS Three transects are set up at each site spaced at 20 m intervals running perpendicular to the depth gradient. A rope is placed along the transect with marked increments of 2 metres. The rope should be stretched between the first and last star picket, weaving in and out of the intermediate pickets. The quadrat must be placed according to Figure, i.e. the bottom right corner of the quadrat lined up with the increment on the rope. Commencing at the shallow end of the transect, on the left hand side, the following measurement are recorded every 2 metres using a 20 x 20 cm quadrat: - seagrass species - shoot density of each species - maximum shoot height of each species - depth (this should not change but may be affected by the tidal regime) - video of transects See *Quantitative data* for methods of collecting this information. REFERENCE SITES These sites are set up similarly to the Seagrass Health sites, there is a central star picket with 4 permanent transects radiating out from this central picket. Each transect has 6 permanent quadrats located along it. Qualitative data, shoot density and videography is taken at the Reference sites. No shoot height or canopy cover measures are taken. See 'Seagrass Health Sites' for details on methodology.

Notes

Credit
Edith Cowan University (ECU)

Credit
Cockburn Sound Management Council (CSMC)

Purpose
To monitor the seagrass health in Cockburn Sound, Owen Anchorage and Warnbro Sound