The impact of the massive mucilage outbreak in the Sea of Marmara on gorgonians of Prince Islands: A qualitative assessment

Abstract

In autumn 2020, a large mucilaginous outbreak was recorded in the entire Sea of Marmara and lasted until summer 2021. Mucilaginous aggregates in the water column and the impacts on gorgonians were qualitatively monitored at Prince Islands. Suspending and drifting mucilaginous aggregates in several forms and sizes were present from April to July 2021. All four main gorgonian species present in the area were observed to be covered with mucilage; some colonies were still healthy, some showed total mortality, while others had partial mortality. The population of the red gorgonian Paramuricea clavata was already severely declined in the area and might be expected to be the worst impacted. Gorgonian populations in the area could potentially recover but the recurring nature of mucilage outbreaks might prevent a recovery by rejuvenation as mucilage deposition mainly impact young colonies. Considering with accelerating climate-driven changes, mucilage outbreaks would probably recur in this semi-enclosed sea with clearly altered environmental conditions. The ecological status is clearly alarming and effective measures need to be taken urgently to prevent the formation of another large-scale and long-lasting mucilage event. The implementation of the recent Action Plan for the conservation of the Sea of Marmara could highly improve the conditions if genuinely applied throughout the basin.