A year of field monitoring: Temperature and salinity fluctuations drive sea star wasting disease prevalence in Baltic A. rubens

Katja Seebass¹, Frank Melzner¹

¹GEOMAR Helmholtz Center for Ocean Research Kiel, Germany

Sea stars are key species in marine benthic ecosystems, contributing to their stability and biodiversity. However, they are vulnerable to environmental stressors and face increasing challenges due to climate change. One striking example is the Sea Star Wasting Disease (SSWD), which has caused mass mortalities in over 20 sea star species, triggering ecosystem shifts and raising concerns as it spreads to new regions. While the origin of SSWD remains unknown, it has been linked to environmental fluctuations and microbiome dysbiosis. This study focuses on SSWD in the Baltic Sea, a region with low biodiversity and high vulnerability to such threats. Asterias rubens, the sole asteroid echinoderm in this area, regulates mussel populations and maintains habitat balance, yet its susceptibility to SSWD and ecological implications remain unexplored. Over the course of one year, we assessed the influence of environmental factors on A. rubens abundance, SSWD prevalence, and microbiome variability. Weekly video monitoring revealed an average prevalence of SSWD symptoms in 10% of the population. Disease prevalence was linked to seasonal fluctuations in temperature and salinity, peaking at 20.7% during summer when surface water temperatures reached 18-22°C and salinity ranged from 11-14 PSU, underscoring the influence of environmental drivers. In a next step, we will analyze seasonal microbial communities associated with A. rubens to understand their role in disease dynamics. This study provides critical evidence of SSWD and its seasonal prevalence in Baltic A. rubens, emphasizing the importance of long-term field monitoring to understand the drivers of ecosystem change.