Effects of small-scale turbulence on copepods: The case of Oithona davisae

  • Saiz E
  • Calbet A
  • Broglio E
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Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . American Society of Limnology and Oceanography is collaborating with JSTOR to digitize, preserve and extend access to Limnology and Oceanography. Abstract We report the effects of small-scale turbulence on the feeding rates of the marine copepod Oithona davisae. Laboratory experiments were conducted under a range of turbulence dissipation rates between 10-4 and 101 cm2 s-3. Net enhancements of feeding were observed only at the lowest, whereas negative net effects appeared only at the highest, turbulence intensities. These results contrast with expectations from an encounter-based model for this copepod species that predicted positive feeding enhancements at all turbulence intensities. This disagreement sug-gests the presence of detrimental effects at moderate and high turbulence intensities, very likely driven by either a lower mechanosensor perception capability or lower capture success. In comparison to other ambush copepods, 0. davisae appears much more sensitive to the presence of turbulence, which might be the result of its strict ambush behavior, whereas copepods like Acartia tonsa or Centropages typicus, which can switch into different feeding modes, appear to benefit more from turbulence. The response of 0. davisae feeding to turbulence in our experiments agrees with recent field observations on changes in the vertical distribution of Oithona as a function of wind-driven turbulence events. Hence, 0. davisae seems to choose those depths where small-scale turbulence favors feeding. Although there was some early evidence suggesting that small-scale turbulence could affect zooplankton behavior and feeding (e.g., Singarajah 1975; Alcaraz et al. 1989), the seminal theoretical work of Rothschild and Osborn (1988) stimulated an intensified effort at quantifying this interaction (e.g., Sundby and Fossum 1990; MacKenzie and Leggett 1991; Saiz et al. 1992). In the last 15 yr, both laboratory experimentation (e.g., Saiz 1994; Landry et al. 1995; Ca-parroy et al. 1998) and modeling exercises (e.g., Ki0rboe and Saiz 1995; Visser and MacKenzie 1998) have demon-strated that the increase in particle contact rates from tur-bulence affects such processes as aggregate formation and planktonic trophic interactions. Theoretically, the (root mean square) turbulence velocity adds to the particle relative mo-tion, enhancing encounter as an inverse function of the ve-locity difference between particles (Rothschild and Osborn 1988; Ki0rboe and Saiz 1995). In the case of zooplankton, the translation of this enhancement in encounter into higher ingestion rates depends on the feeding behavior of the pred-ator (and very likely on the prey response to turbulence). Suspension-feeding and cruising zooplankton seem to ben-efit less by turbulence than ambush and pause-and-travel predators (Ki0rboe and MacKenzie 1995; Ki0rboe and Saiz 1995). Furthermore, turbulence effects depend on the tur-bulence dissipation rate (e). While higher turbulence inten-sities could shift the Kolmogorov scale down into smaller

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Authors

  • Enric Saiz

  • Albert Calbet

  • Elisabetta Broglio

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