Simuliid silk pads enhance tufa deposition

Abstract

Simuliid silk pads and their effect on tufa deposition and biofilm development with respect to current velocity and time of exposure have been 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, thus proving that silk influence periphyton development and serves as biomediator in early stages of tufa formation. Diatom and calcite densities were mainly functions of time, with higher densities of both under moderate velocity. Maximum dimension of calcite crystals wasn’ t affected by the two month time of exposure, with larger crystals found under moderate velocity. We conclude that low winter temperature inhibited intensive calcite precipitation so tufa deposition during winter time happened mainly by trapping and binding microcrystalline calcite. Increased current velocities resulted in a poorer periphyton development and a lesser accumulation of calcite crystals.