Responsible: Sigurd Skaar Eliassen
E-mail: sigurse@student.ibv.uio.no
Supervisors: Bente Edvardsen, Simon Hasselø Kline and Tom Andersen
Aim
The aim of this project is to get a greater understanding of the dynamics of important spring bloom diatoms in the Oslofjord by finding the compensation light intensity of two different diatom genera Chaetoceros and Thalassiosira grown in different salinities. I will also examine how these diatom genera compete for light with another diatom genera Skeletonema in a common garden experiment. By doing this we hope to get a greater understanding of why some species like Skeletonema has had a great decrease in biomass and Chaetoceros have had a more stable biomass in the last decades (since 2006) in the Oslofjord spring bloom.
Background
Marine phytoplankton are one of the most important primary producers in the ocean and are crucial for the availability of organic matter in the earliest stages of marine food webs (Lundsør et al., 2022). Phytoplankton, which belong to the polyphyletic group of organisms known as protists, consist of mostly single celled algae drifting with the currents in the upper layers of the water column. Even though these microscopic organisms account for less than 1% of the photosynthetic biomass, they produce approximately 45% of the global net primary production (Falkowski et al., 2004).
In the last decades there has been recorded a gradual loss of diatom biomass in the spring bloom in the Oslofjord. (Lundsør et al. 2022). The main decrease is the result of decreasing biomass of the genus Skeletonema, while other important diatom genera such as Chaetoceros and Thalassiosira have not had such a decrease and have remained stable in biomass since 2006. A possible reason for this could be their ability to handle higher temperatures and lower levels of salinity compared to Skeletonema (Lundsør et al., 2022). Another possible reason for a change in the phytoplankton dynamic in coastal areas like we see in the Oslofjord could be caused by coastal darkening. An increase of light absorbing molecules of dissolved coloured organic matter (cDOM) transferred to the coastal marine waters from river input could slow down the growth of phytoplankton and shift the spring bloom to a later date (Opdal et al., 2019). In an ecosystem with limited light, we can predict that the phytoplankton with the ability to tolerate the lowest critical light intensity will be able to outcompete other competitors for the available light (Huisman et al., 1999).
Research Questions
- 1. What is the compensation light for the diatoms Chaetoceros and Thalassiosira?
- 2. Do different salinities change the compensation light for Chaetoceros or Thalassiosira?
- 3. Will the diatom with the lowest compensation light be the better competitor for light in the common garden experiment?
- 4. Is the planktoscope a trustworthy tool when quantifying the cell abundances of different diatom species in a common garden experiment?
This project will hopefully give an insight in the compensation light of the diatom genera Chaetoceros and Thalassiosira, and provide more knowledge about why some species like Skeletonema has had a great decrease in biomass and Chaetoceros have had a more stable biomass in the last decades in the Oslofjord spring bloom.