Mapping facial cavities on a lagoonal patch reef on Davies Reef, Great Barrier Reef

Brief description

Systematic description of the surface character of the various reefal elements of lagoonal patch reefs is necessary to help resolve questions in regard to nutrient flow and general trophodynamics within these systems. Davies Reef, east of Townsville, was chosen as a study site to gather relevant background information. Davies Reef consists of a south-easterly aspect, curved (kidney-shaped) coral barrier enclosing a shallow (about 10m deep) lagoon with many patch reefs (bommies), about 50m in diameter. A single, relatively small bommie (1) general size and shape of cavities or depressions of the bommie walls and2) some indication of the biotic make-up on the bommie wall and immediately adjacent. On the basis of this survey, a study to determine the characteristics of nutrient concentrations in waters around and within the bommie was consequently performed (Andrews and Mueller, 1983).

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Twenty reference markers were positioned about the perimeter lip of the bommie. These markers were labelled with alphabetic characters and placed at approximately 4m intervals. The perimeter was then mapped with its scale and shape defined by the perpendicular measurement of the distance from each marker to a central north south transect.From the perimeter markers, vertical lines were then taken down (approximately 8m) to the base of the scree slope. Horizontal lines were then placed at 2m vertical intervals between consecutive vertical lines from the top of the bommie, while face portions (2 x 4m) were drawn and charted.Each of the 4 metre 'columns' were observed by one person according to 2 perspectives. Firstly, a profile was drawn of the face transected by the left-hand vertical line, and of the upper horizontal surface. Then, a frontal view was made mapping the surface structures following a procedural format modified during ongoing consultation by all members of the survey team. Thus a standardised result was obtained between surveyors. The characteristics used in this integrated procedural format of figure drafting are listed in the legend.Cavity LegendDimensions (1-6):1 Hand size2 Arm length3 Greater than arm length4 Torso size5 Complete body size and greater6 Indentation - large, shallow and concaveA Light visible through another entrance/// Chimney - can't see end of a narrow cavity::: Overhang or outcrop - convex -> Cavity continues under-- Approximate top edge of scree slopeS1 Dead coral - solid and unbrokenS2 Sand and siltS3 Scree slopeLiving Features*1 Coral-general*2 -Agaricia like*3 -Millepora like*4 -Acropora like*5 -Porites like*6 -Soft*7 Fish-general*8 Algae-Halimeda like*9 -Ribbon Like*10 Clam-general*11 Sponge-general*12 Feather Duster or Christmas Tree wormThese standardised observations are based on a broadly descriptive interpretation and were decided on because of the lack of any precise measuring equipment, and the need to establish a generally useful survey procedure for covering a large area in a short amount of time with scientifically untrained assistance. The observations are basically physical surface characteristics with some comment on the living elements.The markers were left on the bommie for the following year to allow repeated sampling of chemical and physical parameters. The buoy and markers were removed.

Notes

Credit
Duke, Norman C, Dr (Principal Investigator)