Recruitment of sponges and other sessile organisms in central Torres Strait, Australia (MTSRF Project 1.3.2)

Brief description

A study of recruitment of marine invertebrates around Masig Island and Marsden Island, in central Torres Strait commenced in November 2006 and ended in November 2008.Terracotta settlement plates (11 cm x 11 cm) with well pitted surfaces were deployed at three locations on the northern side of each island, with locations two hundred metres apart. Each location was further divided into three sites, each twenty metres apart. At each site, five plates were deployed, roughly one metre apart, at both six metres and twelve metres depth. The settlement plates were attached to a stainless steel base plate anchored to the reef and rested approximately one centimetre above the reef allowing for settlement and recruitment of organisms on both sides of each plate.The plates were deployed in November, at the start of summer, and in May, at the start of winter. At the end of each season, the top and underside of each plate, which was identified using a small numbered-tag on both sides on one corner, was photographed in situ, removed and a new plate deployed. During the first year plates were also photographed in situ after four months in each season to provide information about the recruitment of benthic organisms within a season.Abundance and percent cover of organisms was assessed from images of tiles displayed by Microsoft Windows XP Picture and Fax ViewerTM on a PC screen. This research was undertaken to assess the recruitment of sessile marine invertebrates in central Torres Strait across seasons and years. Recruitment of the wild commercial bath sponge species, Coscinoderma matthewsi, was of specific interest.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Statement: Taxonomic status still to be verified beyond general group assignations.The northern side of each island was chosen for deployment of settlement plates as it allows greater access and safer diving during most weather conditions.The method of attaching settlement plates to the substrate is described in:Mundy CN (2000) An appraisal of methods used in coral recruitment studies. Coral Reefs 19:124-131.Photographic analysis:An underwater close-up frame was constructed to photograph settlement tiles at a fixed distance and to record site and tile information on its frame. As the aspect ratio of the digital images allowed for the recording of extra information on each image, due to the tiles being square, a four-digit code wheel was built into one side of the frame. The framer was adapted to accommodate either an Olympus C-7070 or Canon IXUS 850IS camera in underwater housings. Both these cameras have identical lenses and sensor-resolution and images produced are comparable in quality and view.The recruitment of sessile organisms to central Torres Strait was determined for both abundance and percent cover. To determine the abundance of each taxa, an overhead transparency marked with a square was overlaid on a PC-screen. All images of tiles were displayed by Microsoft Windows XP Picture and Fax ViewerTM and enlarged by clicking the zoom-in button sufficient times to identify each organism. To measure surface area occupied by each taxa, a forty point grid was overlaid on the PC-screen image. For both abundance and percent cover, the square or grid was reduced by a one centimetre margin to eliminate any potential edge effects.

Notes

Credit
Duckworth, Alan R, Dr (Principal Investigator)