Diversity, distribution and occurrence of adult Caddisflies along the Nan river in Nan province and Their Relationship to the Presence of Macroalgae

Abstract

The Nan River in Tung Chang and Chiang Klang districts in Nan province, Northern Thailand is the one of aquatic habitat containing high diversity of caddisfly. This research was conducted in order to survey and collect the data about adult caddisflies, Kai algae and environmental factors along the Nan River in 4 villages (Ban Pa Pueai, Ban Don Sop Puea, Ban So Den Phatthana and Ban Tuet Villages). Each village had 2 selected sampling sites so the total of sampling sites was eight. The total of 15,513 specimens was caught monthly from January 2017 to December 2018, by portable light traps. Seventy-two species in 10 families and 25 genera were identified. Family Hydropsychidae was the most abundant and common species in distribution and occurrence, represented by 46% of all the identified species followed by Leptoceridae (31%) and Ecnomidae (6%) and five other minor families (totaling 17%). Potamyia johansoni in family Hydropsychidae was a new record species for Thailand. The diversity in the hot and cool seasons was higher than in the rainy season and was higher in upper river reaches than in lower river reaches. The species numbers in two districts were approximately similar but the types of species were different. The study about their distribution found that 11 species were caught in only one site and the others (61 species) were caught in 2-8 sites. The occurrence of 64 species showed that they occurred only in 3 months per year in adult stage, whilst 8 species occurred in 4 to 12 months. Kai algae in the Nan River were in genera Cladophora and Rhizoclonium. Kai algae blooming period was in cool season until hot season (November to March of next year). Average percentages of Kai algae coverage in 8 sampling sites were 0.48 to 56.21% per 1 m2 among the 8 sites. The coverage was the highest in cool season, especially in open areas of agricultural and urban areas. The differences in the monitored environmental factors (air temperature, water temperature, relative air humidity in evening, relative air humidity in morning, nitrate, ammonia, orthophosphate, turbidity, water hardness, dissolved oxygen and biochemical oxygen demand) were not significant among the 8 sites. The values of pH, electrical conductivity, total dissolved solids and water velocity were significant difference (p<0.05). This research indicated that the adult caddisflies, Kai algae and some environmental factors were in relationship significantly (p<0.05), but only one caddisfly species related with the change of Kai algae coverage. All environmental factors depended on natural season change as main impact by 2-years monitoring. Furthermore, the river reaches of Nan River in this research had low disturbance from human activities and were suitable for diversity conservation and be an important natural resource for learning in future.