Mesozooplankton of the Omani shelf: taxonomy, seasonality, and spatial distribution

The total zooplankton biomass was determined for 216 samples collected during seasonal surveys onboard a research vessel. Some of these samples were processed to the level of species. In 2007–2008, the Omani shelf was populated by a highly productive epipelagic plankton community. The chlorophyll- a concentration was high throughout the seasonal cycle and likewise the zooplankton biomass, where seasonal values varied from 543 to 723 mg m −3 . Spatial distribution of zooplankton biomass over shelf waters was highly heterogeneous, with maximal heterogeneity observed during the South-west Monsoon. The mean biomass and size structure of the zooplankton community did not exhibit statistically significant seasonal changes. On the species level, seasonal changes dealt with a massive appearance of the copepod Calanoides carinatus s.f. in shelf waters, to which organisms migrated from the deep, during the South-west Monsoon. The population represented mainly by c4 and c5 copepodite stages ascending to upper layers during its ontogenetic migration has occupied the entire Omani shelf area. However, this migration did not contribute markedly to seasonal variation of the total zooplankton biomass.