الهجرة الرأسية اليومية

بتران قرد البحر (من الهوائم الحيوانية) تساعد الفهماء على دراسة الهجرة الرأسية اليومية.

الهجرة الرأسية اليومية Diel vertical migration (DVM)، وتُعهد أيضاً بإسم diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The migration occurs when organisms move up to the epipelagic zone at night and return to the mesopelagic zone of the oceans or to the hypolimnion zone of lakes during the day. The word diel comes from the Latin dies day, and means a 24-hour period. In terms of biomass, it is the greatest migration in the world. It is not restricted to any one taxa as examples are known from crustaceans (copepods),molluscs (squid), and شعاعيات الزعانف (trout). Various stimuli are responsible for this phenomenon, the most prominent being response to changes in light intensity, though evidence suggests that biological clocks are an underlying stimulus as well. The phenomenon may arise for a number of reasons, though it is most typically to access food and avoid predators. While this mass migration is generally nocturnal, with the animals ascending from the depths at nightfall and descending at sunrise, the timing can be altered in response to the different cues and stimuli that trigger it. Some unusual events impact vertical migration: DVM is absent during the midnight sun in Arctic regions and vertical migration can occur suddenly during a solar eclipse.

الاكتشاف

أثناء الحرب العالمية الثانية the U.S. Navy was taking sonar readings of the ocean when they discovered the deep scattering layer (DSL). While performing sound propagation experiments the University of California's Division of War Research (UCDWR), consistently had results of the echo-sounder that showed a distinct reverberation that they attributed to mid-water layer scattering agents, there was speculation these readings may be attributed to enemy submarines. By collaborating with biologists from Scripps Institution and the UCDWR, they were able to confirm that the observed reverberations from the echo-sounder were in fact related to the diel vertical migration of marine animals. The DSL was caused by large, dense groupings of organisms, like zooplankton, that scattered the sonar to create a false or second bottom.

الأهمية للمضخة الحيوية

المضخة الحيوية هي تحويل ثاني أكسيد الكربون والمغذيات غير العضوية، بالتمثيل الضوئي النباتي، إلى particulate organic matter in the euphotic zone and transference to the deeper ocean. This is a major process in the ocean and without vertical migration it wouldn’t be nearly as efficient. The deep ocean gets most of its nutrients from the higher water column when they sink down in the form of marine snow. This is made up of dead or dying animals and microbes, fecal matter, sand and other inorganic material.

انظر أيضاً

Krill
Phytoplankton
Primary production

الهامش

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^ B. Cisewski, V.H. Strass, M. Rhein, S. Kragefsky (January 2010). "Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea, Antarctica". Deep Sea Research Part I: Oceanographic Research Papers. 57: 78–94. doi:10.1016/j.dsr.2009.10.005.CS1 maint: multiple names: authors list (link)
^ N.S. Hafker, B. Meyer, K.S. Last, D.W. Pond, L. Huppe, M. Taschke (July 2017). "Circadian clock involvement in zooplankton diel vertical migration" (PDF). Current Biology. 27 (14): 2194–2201. doi:10.1016/j.cub.2017.06.025. PMID 28712565.CS1 maint: multiple names: authors list (link)
^ C. Manno, A.K. Pavlov (January 2014). "Living planktonic foraminifera in the Fram Strait (Arctic): absence of diel vertical migration during the midnight sun". Hydrobiologia. 721: 285–295. doi:10.1007/s10750-013-1669-4.
^ K. Sherman, K.A. Honey (May 1970). "Vertical movements of zooplankton during a solar eclipse" (PDF). Nature. 227 (5263): 1156–1158. doi:10.1038/2271156a0.
^ Hill, M.N. (2005). Physical Oceanography. Harvard University Press. p. 499.
^ Steinberg, Deborah; Sarah Goldthwait; Dennis Hansell (2002). "Zooplankton vertical migration and the active transport of dissolved organic and inorganic nitrogen in the Sargasso Sea". Deep-Sea Research Part I. 49 (8): 1445–1461. CiteSeerX 10.1.1.391.7622. doi:10.1016/S0967-0637(02)00037-7. ISSN 0967-0637.