Seasonal dynamics of the protist community in the Oslofjord and Skagerrak in a changing ocean.

Summary

Protists and prokaryotes compose approximately 90% of the biomass in the oceans, and any changes within this microbial community are likely to have reverberating effects throughout the ecosystem. Due to climate coastal marine systems are experiencing increased freshwater discharge from land and a darkening of the water column along with changes in nutrient concentrations. The phenology is also changing and in the inner Oslofjord the spring blooms starts on average 2 weeks later that 15 years ago. The causes for this delay in unclear. In this study we examine the diversity and seasonal dynamics of the protist community by metabarcoding in the inner and outer Oslofjord, and possible changes during 14 years. Monthly plankton samples were collected at two localities and two depths during 2023 and similar samples were collected in 2009-2011, to be sequenced by current high throughput technology (Illumina). Various environmental parameters have been measured including CDOM (colored dissolved organic matter). We ask whether browning or other physico-chemical conditions can explain the delayed spring bloom and other observed changes in the protist community in the Oslofjord and Skagerrak.