Species Composition, Habitat Uses of Acetes Shrimps at Talet Yai Bay, Nakhon Si Thammarat and the Influence of Predator (Secutor insidiator) on Habitat Selection of Acetes japonicus
Abstract:
Species composition and habitat use was studied from June 2010 to May 2011 at Talet Yai Bay, Khanom District, Nakhon Si Thammarat Province. Samplings were conducted in five habitats: Seagrass beds, Muddy flats, Coarse-sand flats, Mangroves and Open water. Acetes shrimps were collected by the Acetes net. The collections were done both in the daytime and at nighttime during high tide. Four species of Acetes were found: A. japonicus, A. erythraeus, A. vulgaris and A. indicus. The results indicated that more Acetes shrimps were collected at night than in the daytime. At night Acetes shrimps had their abundance was highest in coarse-sand flats, followed by mangroves, open water, muddy flats and seagrass beds respectively. A. japonicus was the predominant species in all habitats. Mean abundance of Acetes spp. showed highly significant differences between habitats (p < 0.01). In terms of temporal scale, the analysis of the mean abundance of Acetes spp. shows that they did not differ among monsoon seasons, northeast, inter-monsoon and southwest Z (p > 0.05). However, the mean abundance of Acetes was found highest during inter-monsoon season. According to the co-inertia analysis, the abundance of A. japonicus and A. vulgaris was found positive related to salinity and chlorophyll-a. On the other hand, A. erythraeus and A. indicus did not show relation to any of these environmental factors.
Experiments on the habitat selection of A. japonicus were conducted in a concrete tank (1 meter diameter). Habitat selection of A. japonicus was studied at different levels of vertical in habitats and light intensities. The experimental tank
was divided into four equal sections and one type of artificial habitats in each. These were: bare sand substratum, mangrove habitat (mangrove roots), seagrass habitat, and rocky habitat. The resulted showed that numbers of A. japonicus differed significantly among habitats in daylight (x^2 = 15.70, df = 3, p < 0.01). In contrast, there was no difference in selection between habitats by A. japonicus at night (x^2 = 4.28, df = 3, p = 0.2332). Habitat selection of A. japonicus on horizontal habitats and light intensities were conducted in the experimental tank divided into three equal sections, each provided with one of the following substratum: bare substratum (Yibsum sheet), sand habitat, muddy habitat. The numbers of A. japonicas were found significantly different among habitat types in daylight (x^2 = 9.57, df = 2, p < 0.01). At night there was no significant difference for selection between habitats by A. japonicus (x^2 = 3.26, df = 2, p = 0.1964).
The effects of a predator on habitat selection of A. japonicas was tested by using mucus of Secutorr insidiator. This experiment was carried out in an experimental tank that was divided into 6 equal habitat sections. Artificial habitats were randomly assigned: bare substratum, mangrove habitat (mangrove root), seagrass habitat, rock habitat, sand habitat and muddy habitat. In daylight the presence of fish mucus affected significantly the habitat selection by A. japonicus (x^2 = 20.35, df = 5, p < 0.01). The result showed that shrimps significantly preferred bare substratum to vertically structured habitats. Fish mucus also significantly influenced the habitat selection of A. japonicus at night (x^2 = 13.65, df = 5, p < 0.05). A. japonicus showed highly significant preference for mangrove habitat over other habitats. In addition, the effect of predator detection by means of vision was demonstrated A. japonicus showed no preferential selection of habitats either by day or by night (day: x^2 = 9.86, df = 5, p = 0.0794), (night: x^2 = 3.70, df = 5, p = 0.5937) in response to the visual presence of a predator.
WALAILAK UNIVERSITY. CENTER FOR LIBRARY RESOURCES AND EDUCATIONAL MEDIA