AME 38:71-79 (2005)  -  doi:10.3354/ame038071

ABSTRACT: Tinodes rostocki larvae (Trichoptera: Psychomyiidae) cover large proportions of stream hard substrata with retreats constructed of mineral particles and larval silk. We consider these retreats as 3-dimensional extensions of the epilithic biofilm that may possess a distinct microenvironment, community metabolism and composition. Therefore, we compared the photosynthetic/respiratory activities (O₂ and pH microsensors) and the photopigment composition (HPLC) of larval retreats and the surrounding epilithic biofilms. In retreats, pigment contents and photosynthetic/respiratory activities were highest in sections with a visible microphytobenthic biofilm that were mostly the older parts of the retreats. In contrast, newly constructed sections of the retreats and the surrounding epilithic biofilm had approximately 5-fold lower values. The fucoxanthin-to-chlorophyll ratio of the retreat biofilm was high (fuco/chl a = 1.27) and indicated diatom dominance, which was not evident in the surrounding epilithic biofilm (fuco/chl a = 0.15). Experimental transplantation of larval retreats to microscope slides allowed microsensor measurements through the 500 to 700 µm-thick wall and inside the lumen. In the light, O₂ concentration and pH values increased significantly across the wall and remained high in the lumen of the retreat, whereas in darkness O₂ and pH depressions in both wall and lumen were moderate or even absent. Our data suggest that T. rostocki larvae construct and maintain retreats with a particular physico-chemical microenvironment that favours a distinct microbial community. Thereby, abundant T. rostocki larvae might significantly influence benthic primary production and heterotrophic metabolism in small streams.

KEY WORDS: Stream · Epilithic biofilm · Microalgae · Photosynthesis · Trichoptera · Grazing · Microsensors · Photopigments