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Identifier 000452548
Title Μελέτη των κύριων αβιοτικών και βιοτικών παραγόντων που επηρεάζουν τα φάσματα μεγέθους των πελαγικών οργανισμών
Alternative Title Study of the main biotic and abiotic factors influencing the size spectrum of pelagic organisms
Author Μπατζιάκας, Ευστράτιος Κ
Thesis advisor Λύκα, Κωνσταντίνα
Reviewer Σωμαράκης, Στυλιανός
Καρακάσης, Ιωάννης
Πήττα, Παρασκευή
Ψαρρά, Στυλιανή
Μιχαλούδη, Ευαγγελία
Φραγκούλης, Κωνσταντίνος
Abstract The size of an organism is a “master trait” governing multiple biological and ecological processes. The metabolic rate, the growth rate of the body and body parts, the growth rate of a population, the mortality rate, the maximum lifespan, several reproductive traits, predator-prey relationships and the size-structure of organisms, are few of the processes dependent on the size of the organism. Through the normalized biomass size-spectrum (NBSS) the efficiency of the energy flow from the smaller to the larger organisms can be estimated. The slope of the spectrum reflects the metabolic losses between trophic levels and the losses to the detritus food chain. In the present study, the main factors (biotic and abiotic) influencing the size-spectra of aquatic organisms were investigated. Towards this objective, three case-studies were carried out in three areas of the Aegean Sea, with different physical, hydrological and anthropogenic disturbance characteristics. An extensive review on the published effects on aquatic size-spectra was also carried out. The three areas considered were: a) The broader area of the Saronic Gulf, in which Elefsina Bay is located. Elefsina Bay is a highly impacted enclosed gulf, that exhibits near bottom hypoxia during the summer stratification period. This area was chosen to investigate the effect of hypoxia on the biomass size-spectra of planktonic organisms. b) The Thracian Sea, an area of intense hydrological variability, highly affected by the advection of low salinity and productive Black Sea Waters. The small-scale and depth related effects of said waters on the biomass size-spectra of mesozooplankton was explored. c) The Cretan Sea, which is one of the most oligotrophic areas in the Mediterranean Sea, characterized by the absence of anthropogenic disturbances and high hydrological variability due to the mixing of different water masses coming from the Levantine, the Atlantic Ocean and the Black Sea. Said area was chosen to investigate the stability of the biomass size-spectrum, presented generally in oligotrophic oceans, and the seasonal and interannual variability of the size-spectrum during a six-year period. We found that near-bottom hypoxia during the stratification period in Elefsina Bay severely impacted the slopes and y-intercepts of the biomass size-spectra of planktonic organisms. This was accompanied by concomitant shifts in the distributions of organisms throughout the water column, wherein the picoautotrophic eukaryotes dominated in the hypoxic layer, while mesozooplankton was actively avoiding it. The present study quantifies for the first time the effects of hypoxia on the biomass size-spectra of pelagic planktonic organisms. The results indicate that hypoxia reduces trophic transfer efficiency from the smaller to the larger organisms. 20 The productive, low salinity Black Sea Water intrusions led to the formation of strong fronts in the Thracian Sea, heavily influencing the biomass size-spectra and the distributions of mesozooplanktonic organisms. Stations located on the fronts formed by the movement of the main current presented flatter slopes and higher y-intercepts compared to the closely located (~5 NM) adjacent stations. The productive Black Sea Waters, known to carry dissolved and particulate organic carbon, enhance secondary production and increase mesozooplankton biomass. Depth related effects on the size-spectra and organism distributions were also observed. Slopes were flatter and y-intercepts higher directly above the halocline, wherein the highest mesozooplankton biomasses were recorded. Such a high, small-scale, spatial variability of the size-spectrum parameters is, to our knowledge, demonstrated for the first time. How systems of high hydrological variability evolve through time, is also discussed. Remarkable stability of the biomass size-spectra through time was observed in the Cretan Sea. Both slopes and y-intercepts exhibited very small variability, without any seasonal or interannual pattern. This remarkable stability suggests that, in the hyper-oligotrophic area of the Cretan Sea, the organization of the planktonic trophic web, and especially the contribution of the recycling of the organic matter through the microbial food web, supports a high trophic transfer efficiency throughout the year. The time-series of the Cretan Sea is one of the few published multiyear, with monthly resolution, size-spectra time-series. A multitude of factors influencing the aquatic size-spectra was recorded through extensive review of publicized information. The factors identified refer to the general shape of the spectrum, the physical, topographical and oceanographic variability, the season, the concentration of nutrients, the biological and ecological variability, and the anthropogenic disturbances, including fisheries and climate change. The organism size-spectra are proven to be powerful tools for the assessment and monitoring of the state of aquatic ecosystems.
Language Greek
Subject Aegean Sea
Cretan Sea
Elefsina Bay
Hypoxia
Normalized biomass size spectrum (NBSS)
Plankton
Saronic Gulf
Thracian Sea
Αιγαίο
Θρακικό Πέλαγος
Κρητικό Πέλαγος
Κόλπος Ελευσίνας
Πλαγκτόν
Σαρωνικός Κόλπος
Υποξία
Φάσματα μεγεθών-βιομάζας
Issue date 2022-11-23
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/6/5/1/metadata-dlib-1669973994-239455-26416.tkl Bookmark and Share
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