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BIO-C3 Deliverable No D1.2

Vor Kurzem sorgte die Landung einer riesigen Meerforelle in den sozialen Medien für rege Diskussionen – der Fang erfolgte in der Schonzeit, in der nur blanke Fische entnommen werden dürfen. Silber oder gefärbt? Wir haben einen Experten dazu befragt und nehmen das zum Anlass, mal über die Regelungen nachzudenken

ENDBERICHT (28.06.2013) Gefördert durch das Landesamt für Landwirtschaft, Umwelt und ländliche Räume (LLUR) Schleswig-Holstein, Flintbek, aus der Fischereiabgabe Schleswig-Holstein Förderzeitraum 01.10.2012 – 15.03.2013

Salinity, temperature, and O2 have been recorded on a monthly basis at the Boknis Eck Time Series Station (BE; Eckernförde Bay, SW Baltic Sea) since April 1957 with only two major breaks (1976-78 and 1983-1985). Chlorophyll a measurements started in 1960 and nutrient data (NO2-, NO3-, NH4+, PO4 3-, SiO4 2-) are available since March 1979. Here we present a short introduction to the long-term trends observed at BE and selected results of ongoing projects covering different topics from the surface microlayer and the water column to the sediments at BE. On the basis of a preliminary analysis of the long-term records of surface water temperature, oxygen in 25m, and dissolved nutrients we conclude that BE is affected by both regional processes and global processes detectable as eutrophication and warming of the surface water, respectively. The number of events with extremely depleted O2 concentrations (hypoxia/anoxia) in the bottom layer has been increasing during the last 25 years. Moreover, BE is site of signifi cant emissions of climate relevant trace gases such as methane.

The small pelagic sprat (Sprattus sprattus) is a key ecologic player in the Baltic Sea. However, there is long-term variability in recruitment which is thought to be influenced by fluctuations in abiotic and biotic conditions experienced during the early life stages. This study concentrates on the influence of different ambient salinities on sprat egg development, egg buoyancy and survival as well as early yolk sac larval morphometric traits. Egg buoyancy significantly decreased with increasing salinity experienced during fertilization and/or incubation experiments. Field egg buoyancy measurements in 2007 and 2008 exhibited annual and seasonal differences in specific gravity, potentially associated with changes in adult sprat vertical distribution. Neither egg development time nor the duration of the yolk sac phase differed among salinity treatments. At eye pigmentation, larval standard length exhibited high variance among individuals but did not differ among treatments. The largest ecological impact of salinity experienced during spawning was the modification the buoyancy of eggs and yolk sac larvae, which determines their vertical habitat in the Baltic Sea. There are strong thermo- and oxyclines in the Baltic Sea, and thus salinity can indirectly impact the survival of these early life stages by modifying the ambient temperatures and oxygen conditions experienced., El espadín (Sprattus sprattus) es un pequeño pelágico que juega un papel ecológico clave en el mar Báltico. No obstante, se considera que la variabilidad a largo plazo en el reclutamiento está influenciada por condiciones bióticas y abióticas experimentadas durante los primeros estadios de desarrollo. Este estudio se concentra en la influencia de diferentes salinidades ambiente sobre el desarrollo de los huevos de espadín, su flotabilidad y supervivencia, así como sobre los rasgos morfométricos de las larvas lecitotróficas. La flotabilidad de los huevos disminuye significativamente con los incrementos de salinidad experimentados durante los experimentos de fertilización y/o incubación. Las medidas de flotabilidad en el medio mostraron diferencias en la gravedad específica de carácter anual y estacionales en 2007 y 2008, potencialmente asociadas a cambios en la distribución vertical de los adultos de espadín. Ni el tiempo de desarrollo de los huevos ni la duración de la fase lecitotrófica difirió entre los tratamientos de salinidad. En el estadio de pigmentación de los ojos la longitud estándar de las larvas mostró importante variabilidad entre individuos, pero no entre tratamientos. El mayor impacto ecológico debido a la salinidad experimentada durante la puesta fue la modificación de la flotabilidad de los huevos y larvas lecitotróficas, lo que determina su hábitat vertical en el mar Báltico. En este mar se dan importantes termo- y oxiclinas y, por tanto, la salinidad puede impactar indirectamente en la supervivencia de estos primeros estadios de desarrollo a través de la modificación de las condiciones ambientales de temperatura y oxígeno en las que se desarrollen.

The present thesis investigated the effects of manipulated temperature (range from 5-19°C) and salinity (range from 5-37.2) levels on survival, egg buoyancy, growth, developmental durations and important morphological traits of eggs and non-feeding yolk sac stages of sprat (Sprattus sprattus) originating from two populations from contrasting environments. Experiments were performed with Baltic Sea sprat (brackish) and Adriatic Sea sprat (fully marine) populations and compared to data for the North Sea (English Channel, marine) sprat population extracted from literature data. The aims of the present study were to analyse and parameterize the reaction of the above mentioned traits to different abiotic levels on population basis and to study inter-population similarities and differences. The parameterized results may now be implemented and applied in recruitment studies and individual based models (IBMs). Die vorliegende Arbeit befaßt sich mit dem Einfluß von manipulierten Temperaturniveaus (Bereiche von 5-19°C) und Salzgehaltsniveaus (Bereiche von 5- 37.2) auf die Überlebensrate, Ei-Schwebefähigkeit, Wachstum und Entwicklungsdauer sowie auf wichtige morphometrische Merkmale bei den Eiern und den noch nicht fressenden Dottersack-Larven-Stadien der Sprotte (Sprattus sprattus). Die Experimente wurden mit Populationen der Ostsee Sprotte aus dem Bornholm Becken (Brackwasser) und der Adriatischen Sprotte (salin bis hypersalin) aus dem Golf von Trieste durchgeführt, demnach aus Gebieten mit deutlich unterschiedlicher Hydrographie. Als Vergleichswerte konnten bereits publizierte Daten von Nordsee Sprotten (Englischer Kanal) herangezogen werden. Die Ziele der vorliegenden Arbeit waren zum einen die Analyse und Parametrisierung der beobachteten Reaktionen und Merkmale auf die verschiedenen veränderten abiotischen Einflüsse innerhalb einer Population und zum anderen die vergleichende Analyse zwischen den Populationen. Die parametrisierten Ergebnisse finden zum Teil schon Anwendung, bieten jedoch auch die Möglichkeit, zukünftig in Sprotten-Rekrutierungs-Modellen und individuenbasierten Modellen (IBMs) implementiert zu werden.

The present thesis investigated the effects of manipulated temperature (range from 5-19°C) and salinity (range from 5-37.2) levels on survival, egg buoyancy, growth, developmental durations and important morphological traits of eggs and non-feeding yolk sac stages of sprat (Sprattus sprattus) originating from two populations from contrasting environments. Experiments were performed with Baltic Sea sprat (brackish) and Adriatic Sea sprat (fully marine) populations and compared to data for the North Sea (English Channel, marine) sprat population extracted from literature data. The aims of the present study were to analyse and parameterize the reaction of the above mentioned traits to different abiotic levels on population basis and to study inter-population similarities and differences. The parameterized results may now be implemented and applied in recruitment studies and individual based models (IBMs).

The thermal stratification of the upper water layers in the Baltic Sea varies seasonally in response to the annual cycle of solar heating and wind-induced mixing. In winter, the stratification down to the halocline is almost completely eroded by convection and strong wind mixing. Monthly averaged temperature profiles obtained from the ICES hydrographic database were used to study the long-term variability (1950 to 2005) of winter water mass formation in different deep basins of the Baltic Sea east of the island of Bornholm. Besides strong interannual variability of deep winter water temperatures, the last two decades show a positive trend (increase of 1-1.5°C). Correlations of winter surface temperatures to temperatures of the winter water body located directly above or within the top of the halocline were strongly positive until the autumn months. Such a close coupling allows sea surface temperatures in winter to be used to forecast the seasonal development of the thermal signature in deeper layers with a high degree of confidence. The most significant impact of winter sea surface temperatures on the thermal signature in this depth range can be assigned to February/March. Stronger solar heating during spring and summer results in thermal stratification of the water column leading to a complete decoupling of surface and deep winter water temperatures. Based on laboratory experiments, temperature-dependent relationships were utilised to analyse interannual variations of biological processes with special emphasis on the upper trophic levels (e.g., stage-specific developmental rates of zooplankton and survival rates of fish eggs).