แพลงก์ตอนสัตว์ในบริเวณป่าชายเลนอำเภอสิเกา จังหวัดตรัง โดยเน้นกุ้งและปูวัยอ่อน / ศิริลักษณ์ ช่วยพนัง = Zooplankton in mangrove forest at Sikao District, Trang Province with emphasis on shrimp and crab larvae / Sirilak Chuaypanang
Study on zooplankton community in managrove forest at Sikao District, Trang Province with emphasis on shrimp and crab larvae, was carried out bimonthly from May 1996 to May 1997. Zooplankton samples were taken from 6 stations along the canal by horizontal net towing (103 mu) during the in-coming high tide and highest stagnant period. The zooplankton found in this mangrove consisted of 42 groups from 15 phyla. Average density of zooplankton found was (1.02x(10x10x10x10x10x10))-(3.95x(10x10x10x10x10x10)) ind.100 m-3. Copepod was the dominant group with the relative abundance of 57.87-87.55% of total zooplankton density in each sampling period. Nauplius larvae, pelecypod larvae, gastropod larvae, larvacea and sergestidae were important group collected frequently in the mangrove but the relative abundance of each group was usually less than 20% of total density. The result also showed the diverse trophic groups of zooplankton i.e. the herbivorous copepod and Lucifer, the carnivorous chaegtonath and the mucous net feeding larvacea. This indicates the diversity of food chain and enegy cycling in this ecosystem. Besides, the diversity and abundance of planktonic larvae also suggests the ecological important role of zooplankton in recruitment of aquatic animals. Shrimp and crab larvae were the minor zooplankton group in Sikao mangrove forest. Shrimp larvae were composed of 16 species from 5 families. Average density of shrimp larvae was 42-2,401 ind.100 m-3. The most abundant shrimp larvae was in family Alpheidae followed by family Hippolytidae and family Palaemonidae, respectively. Other shrimp larvae found were in family Penaeidae and family Processidae. On the other hand, 41 species from 12 families of crab larvae were recorded from this area. The range of average density found was 543-27,906 ind.100 m-3. The first three families found in abundance were Grapsidae, Ocypodidae and Xanthidae. Besides the role as important food sources for fish and other aquatic organisms, shrimp and crab larvae found especially alpheid shrimp, grapsid and fiddle crab also supported the recruitment of benthic animals in the mangrove. The distribution pattern of zooplankton particularly, the copepod showed the tendency of high density in the inner part of the mangrove forest, while the reverse trend was noticed from the other zooplankton groups, such as pelecypod larvae, gastropod larvae, foraminifera, cerripedia larvae and sergestidae. There was a significant relationship between the density of zooplankton and the salinity of seawater, beside zooplankton density also exhibited a positive relationship with the abundance of phytoplankton in this area. The results from this study indicates that the Sikao mangrove forest is one of the pristine and productive nature mangrove in Thai water.