The impact of internal waves on mesophotic cold-water coral mounds in the Central Mediterranean. Past, present and hope for the future

Project Information

HopeWaves

Grant agreement ID: 101106265

DOI

10.3030/101106265

Project closed

EC signature date 26 April 2023

Start date 1 September 2023

End date 31 August 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 161 411,52

Coordinated by

UNIVERSITA TA MALTA
Malta

Periodic Reporting for period 1 - HopeWaves (The impact of internal waves on mesophotic cold-water coral mounds in the Central Mediterranean. Past, present and hope for the future)

Reporting period: 2023-09-01 to 2025-08-31

Summary of the context and overall objectives of the project

Marine biodiversity in the Mediterranean Sea faces rapid decline due to climate-driven stressors, particularly the increasing frequency and intensity of marine heatwaves. While shallow ecosystems have been widely studied, mesophotic and deep-water habitats (30–150 m and >200 m) remain poorly characterised and largely unprotected, despite hosting vulnerable benthic communities such as coralline algae and corals. These ecosystems play a crucial role in carbonate production, biodiversity maintenance, and potentially as climate refugia.

The HopeWaves project addresses these knowledge gaps by linking oceanographic processes, particularly internal waves, with the development and resilience of mesophotic carbonate systems. Research activities focused on two submarine banks located between Malta and Sicily in Sicilian channel, the central Mediterranean, selected as natural laboratories to study contrasting geomorphologies and hydrodynamic regimes. The overall objective is to understand how internal-wave activity influences habitat distribution, carbonate production, and the preservation of both recent and ancient bioconstructions.

By integrating seafloor mapping, sedimentological and biological analyses, and long-term oceanographic datasets, the project contributes to a more complete understanding of how physical drivers sustain vulnerable benthic ecosystems. The expected pathway to impact involves producing open-access data and models to inform marine spatial planning, biodiversity protection, and EU policy frameworks such as the Marine Strategy Framework Directive, the EU Biodiversity Strategy 2030, and the Mission Restore Our Ocean and Waters.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The scientific work of the HopeWaves project progressed through three interlinked work packages that together built an integrated understanding of how hydrodynamic processes influence carbonate production and mesophotic habitat development in the central Mediterranean.

Work Package 1 focused on the identification and characterisation of mesophotic carbonate bioconstructions and associated facies. High-resolution multibeam and sub-bottom data were analysed to describe the morphology of two submarine banks located between Malta and Sicily in the central Mediterranean. Detailed sedimentological and petrographic investigations of dredged carbonate samples documented the range of carbonate producers and bioconstruction types across different depths. The work established that areas with irregular topography and steep slopes promoted enhanced water mixing and supported active coralline-algae and cold-water corals growth, whereas smoother surfaces with limited hydrodynamics restricted biogenic activity . This analysis provided the first integrated geomorphological and sedimentological dataset for mesophotic to deep-water carbonate systems in the study area, forming the foundation for the following work packages.

Work Package 2 examined the oceanographic framework controlling these environments, with emphasis on internal-wave activity and its influence on nutrient delivery and temperature variability. Temperature, salinity, and density data from CTD profiles and Copernicus Marine Service archives were processed to determine stratification patterns and the depth of the seasonal thermocline. The Brunt–Väisälä frequency (N²) was calculated to assess vertical stability and to identify potential zones of internal-wave generation. The integration of these datasets with seafloor morphology showed that internal waves interacting with irregular mounds and steep slopes enhanced near-bottom mixing, nutrient availability, and the growth of coralline algae and cold-water corals. This work highlighted the coupling between topography, hydrodynamics, and carbonate productivity that underpins the ecological functioning of mesophotic habitats.

Work Package 3 extended the investigation into a paleoenvironmental context to explore how similar processes operated under warmer-than-present climatic conditions. Fieldwork and laboratory analyses on the Lower Coralline Limestone Formation of Malta were used to reconstruct facies associations representing euphotic to mesophotic settings of the Late Oligocene. Stratigraphic logging and petrographic analysis revealed a vertical organisation of coral-, coralline-algal-, and bryozoan-dominated facies controlled by variations in hydrodynamic energy, light availability, and sea-level fluctuations. These data supported the development of a conceptual model describing how waves, currents, and platform morphology influenced carbonate production and facies distribution through time. The combination of modern and fossil evidence provided a valuable framework for understanding the long-term resilience of mesophotic carbonate systems to environmental change.

Together, these three work packages established a multidisciplinary approach that linked geomorphology, sedimentology, and oceanography to explain the environmental controls on mesophotic bioconstructions in the central Mediterranean.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

This research provided new data on mesophotic to deep-water carbonate environments in the central Mediterranean and on the role of internal waves in shaping their development. By integrating geological, oceanographic, and paleoenvironmental evidence, the project enhanced current knowledge of these poorly explored habitats, contributing to a better understanding of how hydrodynamic processes sustain biodiversity and carbonate production in the mesophotic zone. The results expand the scientific framework for interpreting the functioning of low-light ecosystems and their potential resilience to environmental change.
Beyond the generation of new scientific knowledge, the project delivers openly accessible datasets and a multidisciplinary framework that can support further research on carbonate production, biogenic habitat mapping, and internal-wave modelling. Future developments should include continuous in situ monitoring of temperature and current variability to quantify the frequency and intensity of internal-wave events, as well as high-resolution biogeochemical studies to evaluate carbonate budgets and ecosystem metabolism. These efforts would strengthen the predictive capacity of current models and contribute to the long-term assessment of the resilience of mesophotic and deep-water ecosystems under changing climatic conditions.

Thin section analysis performed during the project (WP1,3)

Interaction of internal waves and irrigural topography (WP1,2)

LCL Core sample analysing during WP3