Near-bottom depletion of zooplankton over coral reefs: III: Vertical gradient of predation pressure

Ruth Motro, Inbal Ayalon, Amatzia Genin*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Many diurnal planktivorous fish in coral reefs efficiently consume zooplankton drifting in the overlying water column. Our survey, carried out at two coral reefs in the Red Sea, showed that most of the diurnal planktivorous fish foraged near the bottom, close to the shelters from piscivores. The planktivorous fish were order of magnitude more abundant near (< 1.5 m) the bottom than higher in the water column. The predation pressure exerted by these fish was assessed by measuring the consumption of brine shrimps tethered at different heights above the bottom on a vertical line which was pulled over the reef. Below 1.5 m above bottom, the shrimps' survival probability sharply decreased toward the bottom. Higher in the water column, survivorship was nearly 100% with little vertical variation. Our results indicate that near-bottom depletion of zooplankton in coral reefs is likely due to intense predation at that boundary layer. Risk of predation by piscivorous fish apparently restricts planktivorous fish to forage near the bottom, with a distribution pattern greatly deviating from ideal-free distribution.

Original languageEnglish
Pages (from-to)95-98
Number of pages4
JournalCoral Reefs
Issue number1
StatePublished - Mar 2005
Externally publishedYes


  • Artemia
  • Fish
  • Piscivores
  • Planktivores
  • Red Sea
  • Vertical gradients


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