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Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them [Elektronische Ressource] / presented by Jan Schulz


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Published 01 January 2006
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Language English
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Alfred Wegener Institute
for Polar and Marine Research
Spatial and temporal distribution patterns
of zooplankton in the central Baltic Sea
and methods to detect them
Thesis to achieve the academic degree
at the University of Bremen
(FB 2 - Biology/Chemistry)
Presented by
born on the 26 May 1974
in Hildesheim, Germany
– Bremen, December 2006 – Schulz, J (2006): Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them.


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The origin of species - Chapter XIV

Schulz, J (2006): Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them.
Thesis to achieve the academic degree of Dr. rer. nat. at the University of Bremen, Germany.
Submitted December 2006. Date of oral examination 16 February 2007.
Regarding of the content unchanged reprint
1 Referee: Prof. Dr. Wolf Arntz
nd 2 Referee: Prof. Dr. Sigrid Schiel
Third party photos, charts and graphics are labelled. Unmarked objects have been designed, visualised or
photographed by the author. All trademarks and industrial property rights occurring in this thesis belong to
their respective owners.
This study was funded by GLOBEC-Germany (BMBF 03F0320D) and Bremerhavener Gesellschaft für In-
vestitionsförderung und Stadtentwicklung (BIS 56008/2-Z).
4 Abstract.
English abstract
The Baltic Sea is the largest semi-enclosed brackish sea in the world and consists of sev-
eral consecutive deep basins. Due to fresh water input, physical processes and topographic
structures pronounced hydrographic stratifications persist. These stratifications are created
from water masses of incompatible densities due to different temperatures and salinities. In
the Bornholm Sea, a central basin of the southern Baltic Sea, a permanent density gradient
is found in a depth of approximately 60 m (halocline) that demarcates less from more sa-
line waters below. During summer another discontinuity layer is found in the upper 20-
30 m (thermocline). This thermocline separates the warm surface water from the cooler
winter water.
In this thesis the utilisation of the hydrographic layers by the dominant zooplankton spe-
cies of the Bornholm Basin was investigated. A total of 832 multinet samples from differ-
ent sites and depths were analysed for zooplankton composition and the relation to ambient
environmental parameters by means of multivariate methods, weighted depth centroids and
individual analyses of the vertical distribution. It was found that certain species and devel-
opmental stages are bound to distinct layers and partially migrate between them during the
season. The aquatic layers put different demands on the physiology of the individual spe-
cies and can therefore be conceived as habitats, determining the vertical distribution. A
total of five different utilisation modes of the water column were identified. These utilisa-
tion modes are closely correlated to hydrographical volumes and represent characteristic
zooplankton assemblages. Differences between the utilisation modes are partially subjected
to seasonal variability. Potential effects of the segregation of the zooplankton community
on the trophic system of the Bornholm Sea are discussed on the basis of the identified utili-
sation modes. Correlations between the heterogeneous habitat utilisation, climatic changes
and an observed regime shift since the 1980s were revealed. Furthermore, to facilitate the
analysis of such data, a software tool was compiled that imports, creates and displays the
various data formats and also performs initial calculations.
When assessing the vertical distribution of plankton using nets the depth integration is a
limiting factor intrinsic to the method, making a precise assessment of zooplankton species
in different horizons more difficult. To solve this problem a new concept for optical in-situ
detection of minute plankton species is introduced. A central aspect in the development of
5 Schulz, J (2006): Spatial and temporal distribution patterns of zooplankton in the central Baltic Sea and methods to detect them.
such a high magnification photographic detection system was the design of suitable illumi-
nation devices, as the amount of light, i.e. the luminous flux, has to be increased exponen-
tially with increasing magnification. The technical solutions presented create a suitable
image illumination using high resolution digital cameras while allowing for simultaneous
estimation of the photographed water volume. The constructed prototype was able to ac-
quire images of plankton and particles in the water and stores them together with their si-
multaneously measured ambient environmental parameters. This system thus allows for a
more efficient data acquisition as compared to net catches.
Deutsche Zusammenfassung
Die Ostsee ist das größte brackige Binnenmeer der Erde und besteht aus einer Abfolge
mehrerer tiefer Becken. Aus Süßwassereintrag, physikalischen Prozessen und topographi-
schen Strukturen resultieren ausgeprägte hydrographische Schichtungen. Diese Schichtun-
gen rühren von Wassermassen her, welche sich in der Kombination der Parameter Tempe-
ratur und Salzgehalt unterscheiden und in der Folge unterschiedliche Dichten aufweisen.
Im Bornholmbecken, einem zentralen Becken der südlichen Ostsee, findet sich in etwa
60 m Tiefe eine kontinuierliche Dichtesprungschicht (Halokline), die geringer saline Was-
sermassen von höher salinen, und dadurch schwereren, darunter abgrenzt. In den obersten
20-30 m findet sich eine weitere, saisonal ausgebildete Sprungschicht (Thermokline), die
warmes Sommerwasser an der Oberfläche vom kühleren Winterwasser über der Halokli-
nen trennt.
In dieser Arbeit wurde die Nutzung der hydrographischen Schichten durch die dominanten
Zooplanktonvertreter des Bornholmbeckens untersucht. Mit Hilfe multivariater Methoden,
gewichteten Dichteschwerpunkten der Tiefenverteilung und individueller Analyse der Ver-
tikalverteilung wurden insgesamt 832 Multinetzproben von unterschiedlichen Stationen
und Tiefen bezüglich ihrer Zooplanktonzusammensetzung untersucht und in Relation zu
den jeweiligen Umgebungsparametern gesetzt. Dabei stellte sich heraus, dass Arten und
Entwicklungsstadien jeweils an einzelne hydrographische Schichten gebunden sind und
teilweise saisonal zwischen diesen wechseln. Diese Schichten stellen unterschiedliche An-
forderungen an die Physiologie der Plankter und können als Habitate aufgefasst werden,
welche die Vertikalverteilung von Arten beeinflussen. Insgesamt wurden fünf verschiede
Nutzungsmodi der Wassersäule identifiziert. Diese Nutzungsmuster sind eng an hydrogra-
phische Bereiche gekoppelt und zeigen charakteristische Zusammensetzungen der Zoo-