AQUALIGHT

New methods of aquatic hyperspectral light field analysis for concurrent characterisation of physical and bio-optical processes at small scales

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 Obiettivo del progetto (Objective)

'There is a growing concern with the marine environment and societies fear the depletion of fish stocks, pollution and possible impacts of climate change such as the loss of biodiversity. Most of the biological diversity in the ocean relies on the presence of phytoplankton as primary producers and the first element in the oceanic food chain. With over 20,000 known species, the importance of these ubiquitous plants as a food source for the pelagos and as a potential sink of atmospheric carbon have been widely recognized. Traditionally, ship-based observations were the main source of oceanographic data but they can only ever provide spot measurements within a highly dynamic and heterogeneous environment. Likewise, satellite-based remote sensing of ocean colour has similar limitations as it can only probe the skin of the ocean. A third approach is currently being implemented which aims to fill this observational gap by deploying autonomous long-term underwater observatories that allow the study of multiple inter-related properties, variables, and processes in real time and over a range of time and space scales. These observatories fundamentally rely on non-intrusive optical measurements for data acquisition and recent technological advances such as the development of hyperspectral sensors have greatly increased their potential applications. For the first time, scientists can obtain non-intrusive continuous measurements at small-scales to observe the dynamics of underwater ecosystems in situ and in vivo. However, there is an urgent need to further develop the underlying theoretical frameworks and analytical methods in order to be able to use these new technologies to their full potential. AQUALIGHT will make an important contribution to this by developing new analytical methods for the detection and identification of phytoplankton functional types and species, including the characterization of dynamical processes such as growth, photoacclimation and turbulent transport.'

Introduzione (Teaser)

Phytoplankton form the basis of the oceanic food web and sustain themselves using sunlight for photosynthesis and nutrients from the surrounding water. However, a rapid increase in phytoplankton can result in harmful algal blooms (HABs) that release toxins into the marine environment.

Descrizione progetto (Article)

Toxins from HABs are harmful to fish and shellfish and can be lethal to humans if such contaminated seafood is eaten. Therefore, HABs can have serious economic consequences for local fishermen and tourism. The AQUALIGHT project addressed this problem, investigating the presence of HABs in Alfacs Bay, a tidal estuary in the north-west Mediterranean.

Scientists combined observations with 3D models to understand the processes behind bloom formation in the Bay. Researchers also identified which environmental conditions encourage bloom development and the phytoplankton species involved.

Computer models were developed to study small-scale processes such as the mixing of the water column due to turbulence, and light availability. A model was also set up to determine the validity of current methods for measuring phytoplankton growth and productivity.

Scenarios for different meteorological conditions were created that showed that under low wind conditions Alfacs Bay experienced typical estuarine circulation. This reduced the residence time of phytoplankton in the bay, which decreased the likelihood of a HAB.

However, high wind speeds caused normal estuarine circulation to break down, increasing residence time and the possibility of a HAB occurring. This is because Alfacs Bay is high in nutrients compared to the open sea, and a longer residence time means better growth conditions for phytoplankton.

Knowledge gained through AQUALIGHT will help scientists make predictions and establish early warning systems for HABs. This will enable policy makers to make informed decisions that help reduce the economic impacts of toxic blooms on the local fishing and tourism industries.

Furthermore, as HAB events occur across the globe, the scientific insights gained through the work of AQUALIGHT can help all communities that face recurring HAB outbreaks.