Benefit assessment on the surface layer algae field used as an intermediate rearing area for seedling release
To enrich the fishery resources of offshore wind power quasi-protected area, we simulated to establish surface layer algae field in Penghu sea area and discussed its possibility of resource enrichment. We established five sets of Sargassum hemiphyllum var . chinense field during December, 2019. After five months, the production of algae was 1,500 kg. Furthermore, we estimated that there were about 14.4 million pieces of creatures attached in the field. The most abundant is Copepods which accounted for 81.0% of the total abundance and then followe by Talitridae for 16.0%, and Caprellidae for 3.0%. About a total number of 9,000 juvenile fish in 12 species and 10 families inhabited around the algae field. The most dominant species were Pelates sexlineatus, Pelates sp., Siganus fuscescens, and Family Mugilidae. The coverage rate of surface layer algae field reached 70% in March. We released fifty thousand of juvenile crabs with an average carapace width of 4.3mm into the algae field on April 6th. The multidimensional space of algae field which provided hidden spaces for crabs could reduce cannibalism. Abundant organisms in algae field also accelerated the growth of juvenile crabs and reduce the breeding cost. The average carapace width was over 20mm after 25 days, which reached the standard of seedling release. Moreover, some juvenile crabs would float with the fallen seaweed and increased population expansion. The result showed that surface layer algae field could be benefit for fishery resource enrichment and crab breeding release.
Technology development on fertilized egg collection, seedling attachment and cultivation of Sargassum glaucescens
The algae matured relatively late so that the fertilized eggs of Sargassum we collected ware less this year. To collect larger quantity and higher quality of fertilized eggs of Sargassum, the investigation of the reproductive cycle of Sargassum was needed. The method we use to collect fertilized eggs was by shaking; however, we needed to develop a more efficient method of fertilized egg collection and attachment in the future. It took 110 days to develop to thallus from fertilized eggs under an ordinary temperature environment.
A preliminary research on establishing bottom layer algae field
The asexual reproduction algae seedlings were successfully planted on one hundred bricks and move to field on December 20th, 2019. The algae attaching on bricks began to fall in the end of April and only holdfasts remained on the bricks after that. The algae bricks with holdfasts were retrieved and kept being observed in culture tanks. In the middle of July, the new seedlings began to grow from holdfasts on the algae bricks. The success of this method increased a new type of algae field, which could diversify the application of algae field. The sexual reproduction algae seedlings of Sargassum hemiphyllum var . chinense and Sargassum glaucescens were also successfully attached on 326 pieces of tiles each on May 11th and July 25th respectively. It took 170 days and 112 days to develop to thallus from fertilized eggs respectively. All of the algae tiles were move to Hongluo bay on November 13th.