The Diversity and Abundance of Gelatinous Zooplankton in the Gulf of Thailand

Abstract

Gelatinous zooplanktons (GZ) are zooplanktons that have jelly-like tissue and have more than 95% of their body made of water. They are diverse and play a role in energy transfer to higher trophic levels, but some species harm humans and affect fishing and aquaculture industries negatively. Knowledge on GZ in Thailand is limited. In this study, GZ samples from the Gulf of Thailand (GOT) collected by the Collaborative Research Survey on Marine Fisheries and Marine Environment in the Gulf of Thailand by M.V.SEAFDEC 2 were analyzed for diversity and abundance. Seventy-six species of GZ from 8 classes and 6 phyla were identified. I found 24 species are new records to Thai water. Class Hydrozoa was the most diverse group with 57 species which accounted for 75% of the total number of species. The Shannon-Weiner index was highest in the middle part of the GOT (St. 15) with a value of 2.85 and was lowest in the upper part of the GOT (St. 1) with a value of 0.92. The highest abundance of GZ was 113,365 individuals/100m³ at St.1 in the upper GOT, and the lowest abundance was 1,753 individuals/100m³ at St. 29 in the middle part of the GOT. Comparing the average abundance for each part of the GOT, the upper part of the GOT had the highest abundance, followed by the middle and lower GOT, respectively. The highest biovolume was 3.26 ml/m³ the upper GOT (St. 3) and the lowest biovolume was found at St. 34 in the lower GOT (0.06 ml/m³). The dominant and common GZ were arrow worm Flaccisagitta enflata and Aidanosagitta neglecta and appendicularian Oikopleura dioica. Non-metric multidimensional scaling showed that GZ communities were divided into 5 groups: 1) The biggest group formed by planktons from the middle and lower part of the GOT. This group has a relatively low abundance and dominated by F. enflata, A. neglecta, O. dioica and hydromedusae Aglaura hemistoma 2) planktons from near shore in the middle part of the GOT which is characterized by high abundance and dominated by F. enflata, O. longicauda, A. neglecta and O. dioica. The third, fourth and fifth groups each consists of a single station from upper GOT and lower GOT that had different dominant species. Shannon-Weiner index and evenness index of the GZ were positively correlated with salinity and seawater density (p<0.01), but negatively correlated with dissolved oxygen (p<0.05). In contrast, abundance and biovolume of GZ were negatively correlated with salinity and seawater density (p< 0.01).