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Influences of turbulence on suspension feeding by planktonic protozoa; experiments in laminar shear fields
Author(s) -
Shimeta Jeff,
Jumars Peter A.,
Lessard Evelyn J.
Publication year - 1995
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1995.40.5.0845
Subject(s) - turbulence , biology , plankton , protozoa , clearance rate , laminar flow , estuary , settling , saturation (graph theory) , ecology , zoology , botany , environmental science , mechanics , physics , mathematics , combinatorics , environmental engineering , endocrinology
Laminar shear below the turbulence microscale can create relative motion between protozoan suspension feeders and their prey, potentially influencing encounter and retention. Theory suggests that ingestion rate may rise sigmoidally with increasing turbulence strength, although interference with feeding mechanisms might occur at some turbulence levels. We measured rates of feeding on fluorescently labeled prey at concentrations below feeding saturation in a survey of cultured bacterivorous and herbivorous flagellates, ciliates, and a helioflagellate over a wide range of shear rates produced in rotating Couette flows. Shears of 0.1–10 s −1 (corresponding to moderate to extremely strong marine and estuarine turbulence) enhanced clearance rates by the aloricate choanoflagellate, Monosiga sp., up to 2.7 × the mean rate in still water. Shears of 110 s −1 enhanced clearance rates by the helioflagellate, Ciliophrys marina, up to 7.0 × the mean in still water. The data are consistent with a sigmoidal response to increasing shear rate. In contrast, clearance rates of the tintinnid, Helicostomella sp., were suppressed at 10 s −1 to as low as 0.42 × the still‐water rate. Several other flagellates and ciliates ( Paraphysomonas sp., two unidentified chrysomonads, Diaphanoeca grandis, Favella sp., and an unidentified heterotrich) showed no significant effects. We hypothesize that the protozoa most susceptible to an influence of turbulence are nonmotile (e.g. Heliozoa, Foraminifera, Radiolaria) or are weak swimmers (e.g. some flagellates and ciliates). Current methods for measuring feeding rates in still‐water incubations may underestimate grazing by these taxa under strong turbulence in the field. Through species‐specific influences on feeding rates, spatial and temporal variations in turbulence may have very selective effects on microbial food‐web dynamics.