Effect of current velocity and case adaptations on the distribution of caddisfly larvae (Glossosoma, Trichoptera)

Abstract

In aquatic systems, oxygen availability is often a limiting factor affecting animal distribution. We documented the distribution of case-bearing caddisfly larvae (Glossosoma) in a riffle of the Hirose River, Japan, and found that larval density increased with increasing current velocity. We also experimentally measured the effect of flow and case morphology on oxygen consumption and mortality. Larvae were divided into ''perforated'' and ''closed'' case treatment groups where gaps in the upper side of the dome-shaped case were left open or closed. They were placed in either lotic or lentic conditions. Oxygen consumption was higher in the lotic compared to the lentic environment for both groups, and was higher in individuals of the perforated-case group than in those belonging to the closed-case group in both environments. Larval mortality was lower under lotic conditions than lentic conditions for the perforated-case group, and higher in the closed-case group in both environments. Our results suggest that larvae prefer areas with high current velocity as they are otherwise unable to obtain sufficient oxygen because of their lack of undulatory behavior. Furthermore, gaps in the larval case appear to enhance passive gaseous exchange via water flow. We also discuss the functional significance of the glossosomatid case.

Glossossoma nigrior (Trichoptera: Glossosomatidae) respiration in moving fluid

“…Oxygen consumption rate of G. nigrior measured in stirred vials from the Hirose River, Japan, was reported to be 11mg O 2 mg -1 larval dry mass (Okano and Kikuchi, 2012). This is similar to the larval tissue consumption rate in our…”

“…The implications of our results support the suggestion by Okano and Kikuchi that larval positioning on the stream bed is driven by oxygen requirements (Okano and Kikuchi, 2012). The results of this simplified laboratory study should be considered in light of the complex array of influencing factors and larval responses in the field.…”

“…The positive relationship between flow rate and larval oxygen consumption is supported by the higher larval oxygen consumption in lotic compared with lentic flow conditions (Okano and Kikuchi, 2012). Oxygen consumption rate of G. nigrior measured in stirred vials from the Hirose River, Japan, was reported to be 11mg O 2 mg -1 larval dry mass (Okano and Kikuchi, 2012).…”

“…Rather, given a certain DO concentration, the stonefly moves until it can achieve its necessary critical oxygen supply (DO × current velocity) (Genkai- Kato et al, 2005). Many members of a third macroinvertebrate order, Trichoptera, undulate their body inside their cases to create an oxygen supply current (Okano and Kikuchi, 2012). In fact, body undulations decrease as fluid flow velocity increases (Feldmeth, 1970).…”

“…Furthermore, Glossosoma do not undulate their abdomens, and larvae readily abandon their cases if damaged and rebuild from scratch (Okano et al, 2010). Furthermore, the glossosomatid case impedes larval access to DO and is abandoned in low fluid flow velocities (Okano and Kikuchi, 2012). More specialized research is necessary to determine the function of the dome-shaped case (Okano et al, 2010).…”