Simuliid silk pads enhance tufa deposition

Simuliid silk pads and their effect on tufa deposition and biofilm development with respect to current velocity and time of exposure were studied during the winter on tufa barriers in Plitvice Lakes (Croatia). Analysis of silk pad types on artificial substrates showed that moderate velocity substrates were slightly more favourable for simuliid larvae as landing attachment site, while they strongly preferred high velocity substrates as wandering attachment sites and exclusively as long term attachment sites for feeding. Although silk covered only 0.78 % of surface area on glass slides, it accumulated 17 % of diatoms and 56 % of individual calcite crystals under moderate velocity conditions and 13 % of diatoms and 41 % of individual calcite crystals under high velocity conditions. This strongly suggests that simuliid silk pads influence periphyton development and serve as biomediator in early stages of tufa formation. SEM analysis has revealed diatoms on the silk with micrite on their mucus strands, indicating diatom synergistic role in tufa deposition. Diatom and calcite densities were mainly functions of time, with higher densities of both under moderate velocity conditions. Maximum dimension of calcite crystals was not affected by the two-month time of exposure, with larger crystals found under moderate velocity. We conclude that tufa deposition during the winter season was controlled primarily by trapping and binding microcrystalline calcite. Simuliid silk changes surface properties, enhancing initial tufa deposits and biofilm development, thereby generating aggregated distribution of initial biofilm-micrite coating on glass slides.