The Influences of Kai Genera Cladophora and Rhizoclonium on Caddisfly Larval order Trichoptera communities in Nan River, Nan Province

Abstract

In the upper part of Nan River, macro-filamentous green algae (genera Cladophora and Rhizoclonium, collectively "Kai" in the vernacular) are usually found in the cobble habitat in the cool season. Caddisfly larvae (Trichoptera) also live in the cobble habitat. Therefore, objectives in this study are as follows; 1) to find out influences of Kai algae on caddisfly larval communities and 2) to study a role of the algae on caddisflies in families Hydropsychidae and Hydroptilidae in term of food resources. Eight study sites in the Thung Chang to Chiang Klang Districts were determined for this study. Samples were collected once a month during January 2017 to December 2018. In the first part of methods, two areas were determined per a study site included Control (CT) and Kai algal blooming (KB) areas during Kai algal blooming period. Less than 20% of Kai algae covering on cobbles within a Surber sample were a Control area. More than 80% of Kai algae covering on cobbles within the Surber sample were a Kai algal blooming area. Kai algal and caddisfly larval samples were collected within 25x25 cm2 of the Surber sample equipment, 10 replicates per one area. In the second part of methods, Hydropsychidae and Hydroptilidae larvae were brought to study about eating behaviors with fresh Kai algae and food items in their foreguts. In the third part of methods, physicochemical factors of air and water temperature, water velocity, pH, electrical conductivity (EC), total dissolved solids (TDS), dissolved oxygen (DO), biochemical oxygen demand (BOD5), water hardness, ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N) and orthophosphate (PO43-) in the Nan River were measured once a month. Thirteen and fifteen families of caddisfly larvae were found in the CT and KB areas, respectively. Number of families of caddisfly larvae in the KB areas were significantly higher than the larvae from CT areas at p< 0.05. Densities of caddisfly larvae in 13 families from the KB areas were significantly higher than the CT areas. These results indicated Kai algae had positive effects to 13 families of caddisfly larvae. Kai algal eating behaviors were found in Hydropsychidae and Hydroptilidae larvae. Hydropsychidae larvae ate fresh filaments of Kai. Hydroptilidae larvae ate cell fluids of fresh Kai algae. Food items in 18 Hydropsychidae larval foreguts from CT areas were 4 types by area included 44.66% of Kai algae (KA), 32.18% of other items such as plant and insect remain (OI), 22.17% of diatoms (DT) and 0.46% of other filamentous algae (OFA). Food items in 18 Hydropsychidae larval foreguts from KB areas were also 4 types by area included 78.13% of KA, 14.49% of DT. 3.72% of OI and 3.65% of OFA. Proportion of KA type in the larval foreguts from the both areas was higher than other food item types. Proportional comparison about the same food types in the larval foreguts from the CT areas with KB areas found that proportions of KA and OFA types in the larval foreguts from the KB areas were significantly higher than the CT areas. But proportions of DI and OI types in the larval foreguts from the CT areas were significantly higher than KB areas. The results showed that Kai algae were important food sources for these larvae. Environmental factors in the Nan River, included water temperature, pH, EC. TDS, turbidity and water hardness associated with occurrences of caddisfly larvae. This study found that the environmental factors in the Nan River during the cool season to the summer were suitable for living of caddisfly larvae.