Natural growth, population dynamics and optimal harvest regime for Coscinoderma matthewsi in Torres Strait (CRC-TS Project: Task Number T1.6a)

At Kodall North and Masig North, adjacent to the farming studies, four 5 x 5 m permanent quadrats were set up at a depth of 10-12 m. Kodall North and Masig North are approximately 2 km apart, while the four 25 m² quadrats at each site were at least 20 m apart. Each quadrat was thoroughly surveyed for Coscinoderma matthewsi, with the position of every sponge recorded on a data sheet divided into 1 m² quadrats. Quadrats were monitored every three months from December 2004 to June 2006. To examine Coscinoderma growth over time, approximately 6 sponges in each 25 m² quadrat were individually labelled, using a tag nailed next to each sponge. Every three months, each sponge was photographed next to a ruler to provide a scale and its width was measured to the nearest 1 cm. Sponge area was determined using the graphics program ImageTool (version 3). Sponge area and width were them multiplied to calculate the volume of each sponge. To examine growth of wild Coscinoderma matthewsi over time, percent growth rates were calculated. At Masig North, in December 2004, 10 sponges had either one-third or two-thirds of their biomass removed; the remaining portion was left still attached to the substratum. The harvested sponges were cut with a bread knife, making a clean cut, and were used in the farming experiments to produce explants. Each Coscinoderma matthewsi was individually labelled, with a tag nailed to the substratum adjacent to the sponge. In addition, 5 non-harvested sponges from the same area were also tagged and monitored to determine the effect of harvesting on growth and survival. Sponge size was determined using the technique described above. Sponges were measured immediately before harvesting, immediately after and in June 2005 (6 months post harvest) and March 2006 (15 months). This study was undertaken to:1. determine growth rates of Coscinoderma matthewsi over time under natural conditions2. develop the knowledge base for sustainable management of natural populations of target species for seed stock supply to farms