Surveys of benthic habitats and zonation in Florence Bay, Magnetic Island, north Queensland

Full description

In April 1989, the marine habitat at Florence Bay, Magnetic Island was surveyed. Initially, manta tows (a snorkeller towed slowly behind a small boat) were made to provide an overview of the area to be surveyed. A series of survey points were established to allow the positions of all survey stations to be determined. A bathymetric map of the bay was also compiled based on 12 echo sounder traverses.A diver-operated underwater video camera was towed over 19 evenly spaced paths in order to assist interpretation of the bay's main biological features. Some of the transect footage was used with hand-held material to produce a video documentary of the bay's main features. A subset of the videotapes was sampled to determine the distribution and relative abundance of major benthic categories along the tow paths.Forty line transects, 20m in length, were used to estimate the cover of benthic organisms and substratum. Corals in the line transects were identified to species level and where necessary, a specimen was collected for taxonomic determination in the laboratory. The maximum diameter of each coral intercepted along each transect was estimated to obtain a size frequency distribution of corals.
This research was undertaken to describe the physical and ecological structure of Florence Bay. This information was used to assess the potential impact that a resort would have on the marine ecosystem of the bay. Tasks identified were:1. to generate a bathymetric map of Florence Bay2. to characterize the hard bottom marine habitats of Florence Bay (the southern rocky shore, and the coral reef) with a focus on coral communities
A survey of the marine benthic flora of Florence Bay was also conducted by Karen Edyvane and R. de Nys as part of this project.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Mapping and sounding:Four survey flags were established at prominent landmarks around the bay. These were used to fix the positions of 10 marker buoys placed at approximately even intervals around the outer perimeter of the coral reef.The 12 echo sounder traverses and soundings were approximately 30 metres apart, resulting in a 30m grid of depth readings. Positions were determined using the radar on board the research vessel Lady Basten, anchored in the entrance to the bay. The depths were plotted on a line tracing of an aerial photograph of the bay, and the bathymetric contours interpolated visually.Video Transects:Two types of video transects were undertaken:1) Profile tows from shore to sandy floor: The tape was stopped each second and the category beneath a target in the centre of the screen scored (200 to 250 points per tow). The ten-point running frequency was determined for each attribute, and the ten-point running means of these frequencies were plotted against tow position.2) Zone tows, where tows were made within homogeneous areas: The tape was divided into segments equivalent to approximately 100m of sea floor, stopped at 200 random intervals and the attribute beneath a target in the centre of the screen scored.Both techniques utilised a video-pc interface developed by KF Navin and E Gill at AIMS, and software developed by KF Navin.Line Transects:The reading on a tape measure was recorded each time it intercepted the edge of a benthic category (such as a coral of a particular species). This method is commonly used in estimating coral coverage (see Loya 1972).The line transects were placed so as to provide an even coverage of the bay's two main hard-bottom biotopes, the southern rocky shore and the coral reef. Lines were usually placed in areas which were deemed 'representative'. However, lines were also placed in areas which were interesting because they were not representative, specifically: areas of high coral cover and/or large colony size in areas elsewhere dominated by algae. This approach precludes the use of statistical analyses based on random sampling, but reduces the probability of inadvertently failing to document interesting areas.Coral growth form categories:Branching coralPlate AcroporaEncrusting coralMassive coralFoliaceous coralNon-coral benthos and substrate categories:AlgaeSandRubbleBare RockLoya Y (1972) Community structure and species diversity of hermatypic corals at Eilat, Red Sea. Mar. Biol. 13:100-123.Natural history observations:Features of interest not falling under line transects were recorded in field notes. Interesting looking areas on an aerial photograph of the bay were examined in situ. and notes taken on their main features. The taxonomic reference for coral identification was:Veron JEN (1986) Corals of Australia and the Indo-Pacific. Angus and Robertson,Sydney. 644pp.

Notes

Credit
Done, Terence J (Terry), Dr (Principal Investigator)