|Titel:||Effects of salinity on reproduction - and behaviour of round goby Neogobius melanostomus in the Baltic Sea||Sprache:||Englisch||Autor*in:||Niemax, Jan||Erscheinungsdatum:||2021||Tag der mündlichen Prüfung:||2022-04-12||Zusammenfassung:||
Over the last centuries, the conditions and inhabitants in many ecosystems changed. This applies likewise to the relatively young Baltic Sea. It is a not fully occupied ecosystem and therefore vulnerable to disturbance by newly introduced species. One of the most successful invaders of the Baltic Sea in the last decades is the round goby Neogobius melanostomus. This bottom-living gobiid species was first observed in the early nineties in Puck Bay Poland and subsequently spread over wide areas within the Baltic Sea. Due to the changing salinity conditions from nearly freshwater in the Bothnian Sea up to nearly full marine in the Kattegat, the Baltic Sea is not uniquely well suited for round goby. For adult round gobies, some studies on salinity tolerance exist. But for a full understanding and forecast of further dispersal also the ability to reproduce in higher salinities needs to be considered. The knowledge in this field is still very limited and will hence be a focus of this thesis. Moreover it is known that there is a difference in the salinity tolerance of adult gobies depending on whether they originate from fresh water or salt water, which was the motivation to conduct a salinity preference experiment with a comparison of round goby from the brackish and freshwater origin.
The first question in this context is about the ability of round goby to bread eggs in different salinities. The ability of round goby eggs to develop in different combinations of salinity and temperature typical for the Baltic Sea, was investigated in a full factorial design. Temperature mainly affected the development time, whereas hatching success was strongly influenced by the salinity. Hatching success was generally low at 10°C but best in 5 PSU and decreasing with rising salinity. At 5 and 10 PSU hatching success declined with increasing temperature from 15°C to 20°C while at 15 and 20 PSU hatching success remained stable with high variability between clutches. The highest hatching success overall was found 5 and 10 PSU at 15°C.
To further clarify which life stage of limits mostly the spread of round goby into areas with higher salinities an experimental approach was used to determine post-hatch growth and mortality rates. An aquarium experiment was condicted to disentangle the salinity influence on length growth, weight gain, and survival of round goby larvae. Larval hatching success was very low at 25 PSU and larvae hatched at 25 PSU did not survive longer than one day. Whereas larvae that were older than 20 days at exposure (hatched at 15 PSU) survived salinities of 29PSU for 10 days. The length growth of larvae was not significantly affected by salinity, in contrast to the weight at length that was highest at 10 PSU. Moreover we conducted first tests of spAARS measurements as a possible proxy of growth, which is till today mainly used in zooplankton. This method did not deliver the expected results, and no clear correlation between spAARS and growth could be established
Finally, the question of salinity preferences of adult round goby from freshwater and brackish water populations was addressed with a shuttle box experiment. The challenge was to provide a suitable experiment setup that worked for the specific behaviour of this species. Used was the most suitable setup, a shuttle box, in which round gobies from freshwater and a brackish water habitat were exposed to the choice of salinity. Slight differences in salinity preference between the different origins (brackish and freshwater) were found. Both preferred salinities below 20 PSU. Fish from freshwater showed a tendency to lower salinities (below 15 PSU) in comparison to those from brackish water. Moreover, while 1/3 of brackishwater fishes stopped shuttling in high salinities 2/3 of the freshwater fishes did. This stopping of the shuttle behaviour indicates a higher physiological stress for the freshwater fish.
|Enthalten in den Sammlungen:||Elektronische Dissertationen und Habilitationen|
Dateien zu dieser Ressource:
|Dissertation Jan Niemax 2021_Dissputationdate.pdf||0ff250b738c8e7c289505f1c187d9eb6||2.97 MB||Adobe PDF||Öffnen/Anzeigen|
geprüft am 21.03.2023
geprüft am 21.03.2023