Abundance and size of the sponge, Coscinoderma matthewsi, in central Torres Strait (MTSRF Project 1.3.2)

Brief description

In March 2007, November 2007 and May 2008, between 6 and 11 sites were surveyed on the coral reefs at Keats Island and Yorke Islands (Masig Island and Kodall Island), in central Torres Strait, to determine the abundance and size frequency patterns of Coscinoderma matthewsi. Sites were located at least 1 km apart and at each site, surveys were conducted at both shallow (4-6 m) and deep (10-12 m) depths, with the former generally on the reef flat. Three 20 x 1 m transects were examined at each depth, with transects separated by at least 20 m to retain independence. For each transect, divers recorded every Coscinoderma matthewsi found within 1 m of one side of the transect line. For each transect, environmental factors such as the degree of reef slope and the percentage of dead coral rubble, sand and consolidated limestone rock, free of living organisms were estimated. For each sponge, the substrate type that it was attached to and growing on was recorded. The habitat in which each sponge was growing was also classified as either exposed (living in an exposed microhabitat, such as on top of rock fully exposed to the ambient water flow) or sheltered (in a sheltered microhabitat, such as under an overhang or protected between surrounding rocks). Sponges were also examined for signs of disease.To examine size frequency distributions patterns, the greatest length, width and height of every Coscinoderma matthewsi was measured with a ruler. For graphical interpretation, sponges were grouped into 2 cm size classes. Some individuals of Coscinoderma matthewsi in Torres Strait have a palmate morphology, where large lobes project upwards from the main sponge base. For each measured sponge, the number of lobes were counted and recorded. This research was undertaken to gather further information on the abundance, size frequency patterns and preferred habitat of Coscinoderma matthewsi on the reefs around Keats Island, Masig Island and Kodall Island, where previous surveys indicated that Coscinoderma matthewsi was most abundant. The results of these surveys were compared with previous surveys undertaken under the CRC-TS Project in July 2004, December 2005 and November 2006, to determine whether the abundance of Coscinoderma matthewsi varies around Masig Island over time. Keats, Kodall and Masig are sand cays, low-lying (<10 m in height) and small in size (<5 km²). Coral reef surrounds all islands, with broken reef connecting Kodall and Masig. The coral reef slope generally starts at a depth of 6 m (MLW) and stops on sand at 15 m, descending at an angle ranging from 20 to 60°. South-easterly trade winds (15-20 knots) are common from April to December, while monsoonal weather patterns with more northerly winds dominate during summer.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Substrate types on which sponges were attached:Three types were identified: rock; rubble; and sand, with grain size ranging from 0.5-2 mm. These three substrate types vary in their level of stability for sponge attachment and growth, with rock providing a secure immobile base for sponges, while sand being easily moved by water currents is a relatively insecure and fluid substrate for attachment. Rubble provides an intermediate level of stability; a separate study at Masig has found that rubble pieces (with a sponge attached) can move several meters between monitoring events (3 months), at times causing the sponge to become partially buried by rubble or sand.

Notes

Credit
Duckworth, Alan, Dr (Custodian)