Prince Albert II of Monaco Foundation

This study presents a one-year microbiological monitoring campaign conducted at the Oceanographic Institute of Monaco to evaluate microbial dynamics within a large public marine aquarium. The approach combined automated near-real-time flow cytometry, culture-based analyses, species identification, and antibiotic susceptibility testing. Continuous bacterial enumeration using the BactoSense® cytometer enabled high-resolution tracking of intact bacterial counts (ICC) across five hydraulic sectors, from seawater intake to exhibition tanks. The results revealed pronounced spatial gradients, with mean ICC values decreasing from 1.4 × 10⁵ cells mL⁻¹ at intake to below 1.3 × 10⁴ cells mL⁻¹ in internal tanks, confirming the high efficiency of UV-C disinfection and filtration systems. Seasonal analysis showed clear fluctuations at the intake, with peaks in spring and early summer associated with increased biological activity in the surrounding Mediterranean environment. Sector-specific variations indicated that hydraulic configuration and residence time influenced microbial stabilization, with localized differences in UV efficiency detected through near-real-time monitoring. Complementary bacterial identification revealed the presence of several opportunistic taxa, including V. fortis , V. harveyi , and Shewanella spp., typical of recirculating seawater systems. Antibiotic susceptibility testing revealed heterogeneous resistance profiles, with β-lactam resistance observed in several Vibrio isolates and multidrug resistance detected in S. algae and V. jasicida . The integration of biosensing, microbial identification, and resistance profiling provides an operational framework for evidence-based microbial surveillance in marine aquaria. These findings highlight the potential of automated near-real-time cytometry to enhance preventive management, support targeted interventions, and ensure microbiological stability in closed aquatic ecosystems. • First long-term marine use of the BactoSense® automated near-real-time flow cytometry system. • One-year monitoring revealed spatial and seasonal bacterial dynamics in a public aquarium. • UV-C disinfection and filtration reduced bacterial loads by more than one order of magnitude. • Hydraulic design and residence time shaped microbial stability across aquarium sectors. • Detection of opportunistic and resistant bacteria supports evidence-based aquarium management.

The Paris agreement target of limiting global surface warming to 1.5-2°C compared to pre-industrial levels by 2100 will heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global- and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions towards a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.