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Volume 14, issue 4 | Copyright

Special issue: Coastal marine infrastructure in support of monitoring, science,...

Ocean Sci., 14, 783-800, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 Aug 2018

Research article | 09 Aug 2018

Acoustic Doppler current profiler observations of migration patternsof zooplankton in the Cretan Sea

Emmanuel Potiris1,2, Constantin Frangoulis1, Alkiviadis Kalampokis1, Manolis Ntoumas1, Manos Pettas1, George Petihakis1, and Vassilis Zervakis2 Emmanuel Potiris et al.
  • 1Institute of Oceanography, Hellenic Centre for Marine Research, Heraklion, Crete, 72100, Greece
  • 2Department of Marine Sciences, School of the Environment, University of the Aegean, Mytilene, Lesvos, 81132, Greece

Abstract. The lack of knowledge of the mesopelagic layer inhabitants, especially those performing strong vertical migration, is an acknowledged challenge. This incomplete representation leads to the exclusion of an active carbon and nutrient pathway from the surface to the deeper layers and vice versa. The vertical migration of mesopelagic inhabitants (macroplanktonic and micronektonic) was observed by acoustical means for almost 2.5 years in the epipelagic and mesopelagic layers of the open oligotrophic Cretan Sea (south Aegean Sea, eastern Mediterranean) at the site of an operational fixed-point observatory located at 1500m depth. The observed organisms were categorized into four groups according to their migration patterns. The variability of the migration patterns was inspected in relation to the physical and biological environmental conditions of the study area. The stratification of the water column does not act as a barrier for the vertical motion of the strongest migrants that move up to 400m every day. Instead, changes in light intensity (lunar cycle, daylight duration, cloudiness) and the presence of prey and predators seem to explain the observed daily, monthly and seasonal variability. The continuous presence of these organisms, which are capable of vertical motion despite the profound circulation variability at the site of the observatory, implies their presence in the broader study area. The fundamental implications of the above regarding biogeochemical processing in oligotrophic seas due to the intimate link between the carbon (C) and nutrient cycles, are discussed.

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Zooplankton and fishes found below a depth of 200 m may perform a vertical migration to the surface waters. The migration patterns (from 400 m to the surface) of four groups of organisms were studied in the deep (1500 m) eastern Mediterranean (Cretan Sea) for 2.5 years. The lunar cycle, daylight duration, cloudiness and presence of predators and prey explain their migration variability. This phenomenon is important as it constitutes an active transport of organic matter over large distances.
Zooplankton and fishes found below a depth of 200 m may perform a vertical migration to the...