MEPS 238:91-100 (2002)  -  doi:10.3354/meps238091

Expansion and homogeneity of the vertical distribution of zooplankton in a very deep mixed layer

Viviana Farstey1,*, Boaz Lazar2, Amatzia Genin3

1The Interuniversity Institute for Marine Sciences, H. Steinitz Marine Biology Laboratory, POB 469, Eilat 88103, Israel
2The Institute of Earth Sciences and Moshe Shilo Center for Biogeochemistry, The Hebrew University, Jerusalem 91904, Israel
3The Interuniversity Institute for Marine Sciences and Department of Evolution, Systematics and Ecology, The Hebrew University, POB 469, Eilat 88103, Israel

ABSTRACT: During stratification over 70% of the zooplankton >100 µm in the Gulf of Aqaba (Eilat), Red Sea, resided in the upper 100 m. In the course of winter mixing, the vertical pattern became more homogeneous, reaching an almost complete uniformity when the vertical mixing exceeded 500 m depth. The zooplankton expanded its vertical distribution throughout the mixed layer. However, full homogeneity, such as would be expected for a passive tracer and observed for phytoplankton, occurred for zooplankton only in the upper section of the mixed layer. Homogeneity occurred for zooplankton passing through 750 µm mesh but not for larger crustaceans. The copepod Pleuromamma indica retained its diel vertical migration regardless of mixing but expanded its nocturnal range under mixing conditions. The observed homogeneity of zooplankton could have been reached either by passive entrainment with the mixing water or by isotropic swimming of the animals, or both. The ecological implications of the expansion of zooplankton distribution for predator-prey relationships and particle fluxes are discussed.

KEY WORDS: Plankton · Vertical mixing · Red Sea

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