The influence of turbulence on vertical distribution of zooplankton in shallow, kinetic Lake Balaton (Hungary)

Abstract

P1anktonie organisms 1ive in the pe1agie zone of open waters and are adapted to survive in this turbu1ent environment. Some experimenta1 resu1ts supported that a moderate turbu1ent intensity is benefieia1 for the funetion o f the zoop1ankton (SAIZ & ALCARAZ 1991, 1992, WISSER & STIPS 2002); however, above a eritiea1 turbu1enee va1ue some organisms may suffer. Some researeh has hypothesized that the maximum body size of a p1anktonie organism eannot be 1arger than ha1f the diameter o f the smallest eddies oeeurring in a downward easeade o f propagating eddies or organisms would get broken by the shear forees (MARGALEF 1978, REYNOLDS 1992, 1998, O'BRIEN 2002). Lake Balaton is the 1argest shallow 1ake in Central Europe, and the vertiea1 spaee for the kinetie energy dissipation is very 1imited by its 3.25-m water eolumn. Therefore, the estimated (MAcKENZIE & LEGGERT 1993) energy dissipation rate is high and the diameter ofthe smallest eddies are very small (6.19 10-5 em see-3 and 0.33 mm, respeetively, at the 3.2 em seemean wind veloeity in the 1ake area). The transient eharaeter ofthe vertica1 strueture of zoop1ankton assemb1ages in Lake Ba1aton suggests that small-seale turbu1enee ean be a major environmental faetor for the vertieal distribution and migration of the organisms in this kinetie lake. The aim of our study was to deteet first the effeet of the RMS turbulenee (root-mean-square of the time series ofthe 3-D individual veloeity magnitude values) on the vertieal segregation and diumal migration ofzooplankton assemblages in the lake.