Differential Growth Rate Studies in Cultured Commercial Sponges |
The objectives of this five-year project, which was initiated under the CTSA Sixth Annual Plan of Work, are to:
Sponges grow very slowly, taking at least two years to reach market size. However, sponge growth rates vary widely; even sponges planted side by side grow at different rates. By determining the cause of growth rate variations, this project will improve the efficiency of sponge farms, thereby increasing the profitability to farmers.
Objective: Improve the efficiency of commercial sponge farms.
Dr. Michelle Kelly-Borges, a sponge systematist and ecologist designed several experiments for the project. These experiments are examining whether:
Wild sponges in the Pohnpei lagoon have three distinct morphologies: spherical or ball-shaped, vasiform or bowl-shaped, ring-shaped and digitate, which have small, finger-like extensions from the surface. Cuttings were taken six zones-the outside top, the inside top, the outside middle, the inside middle, the outside bottom and the inside bottom of the sponge-within each sponge morphotype. Vasiform sponges have no inside top, and ring-shaped sponges have only the outside-top and outside bottom. A minimum of three parent sponges of each morphotype and a minimum of 10 cuttings from each zone were required for statistical purposes.
Three parent sponges of each of the four morphotypes were selected, divided into the six zones and cut. Approximately 900 cuttings were then tagged and planted by zone group. After four to five weeks, 10 or more healthy cuttings from each zone group were selected and placed into a basket. Cuttings were randomly selected from this basket and replanted for 12 to 18 months.
In January 1997, 24-month growth measurements were taken from these sponges. The sponges continued to exhibit a wide range of growth rates, ranging from a low of 2 percent to 3 percent to a high of more than 12 percent. The average monthly growth rate for all groups of sponge cuttings was from 5 percent to 7 percent. The data gathered is being analyzed by Dr. Kelly-Borges. However, a number of preliminary conclusions can be drawn from the raw data.
An investigation was conducted to determine how environmental conditions affect sponge growth rates and the final morphology of cultured sponges. A minimum of 10 cuttings taken from the six areas (top inside, top outside, middle inside, middle outside, bottom inside and bottom outside) of both vase-shaped and ball-shaped parent stock were planted 15 meters deep at three sites:
Each of the three sites was planted with 110 cuttings comprising 10 cuttings from each section of each of the two parent morphologies. Each cutting was tagged with identification regarding the parent shape and the section from which it was taken. The start of this experiment was delayed because of difficulty in finding a ball-shaped parent sponge large enough to supply the necessary cuttings. All the planting was completed in November 1996. The first growth measurements will be taken under the fifth and final year of this project. Investigators measure oxygen levels, carbon dioxide levels and salinity levels once a week at all three sites. In addition, temperature, tide flow and water clarity are measured once a week at all three sites.
Objective: Maintain the existing demonstration farm.
Under the CTSA-funded "Sponge Aquaculture Demonstration Project," five nursery areas were planted with more than 10,000 sponges. Two of these sites have been used for the growth experiments, and the other three sites provided cutting material to help local residents establish private sponge farms. Approximately 4,600 sponges from the nursery areas were provided to sponge farmers.
The nursery sites have also been used as training sites to train local people in sponge farming techniques. From late 1993 through 1996, 10 individuals started the training courses offered at these sites. Six of them started private sponge farms in Pohnpei's lagoon.
Although a variety of fouling organisms normally grow on sponge planting lines, in two areas of the nursery a species of colonial tunicate found growing on the surface of the cultured sponges caused the sponges to be misshapen. The nursery site was monitored monthly, and the tunicates were cleaned off the sponges and lines. Project personnel continue to monitor the tunicate and clean the sponges and growing lines monthly.
A large number of the hanging lines used to suspend the sponges from the growing lines had broken and were replaced with heavier test lines. In addition, a number of the main growing lines had broken and were replaced. Project personnel continue to replace the growing lines and the main lines.
The project investigator gave two presentations at the 1997 meetings of the World Aquaculture Society. One presentation covered sponge farming in general and progress toward establishing a new aquaculture industry in Micronesia. The second talk reported growth data generated in this project. In addition, project personnel presented a poster session on sponge aquaculture techniques used in Micronesia from the 1930s to the present.
Growth, environmental and morphological data will be collected, analyzed and compared during the fifth year of the project.
This project has shown that sponges with high growth rates retain those high growth rates when cut into smaller pieces and replanted and should be used to replant and expand commercial farms to increase their efficiency and profitability. By the same token, slow-growing sponges retain their slow growth rates after being cut and replanted, so they should be harvested and sold as soon as they reach minimum size.